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Hewett 1970

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(Sand dunes at Dyfi NNR - picture courtesy Mike Alexander NRW)

The coasts of both North and South Wales are well known for their wonderful sandy beaches, making them popular holiday destinations for visitors from the UK and many other parts of the world. Behind many of these beaches are sand dune systems which provide homes for diverse forms of wildlife including plants and insects, some so highly specialised that without these dune habitats, they might well be driven to the point of extinction.

Many of our sand dune systems are covered by both UK and international legislation in order to protect their habitats and the species that depend upon them. Despite these designations there is an increasing recognition that all is not well with our sand dunes. Many species could soon become extinct unless we undertake important work to reverse some of the results of earlier interventions, undertaken in good faith, that have damaged the habitats and contributed to a decline of the wildlife species that live within them.

How sand dunes develop and mature - picture from Fascinated by Fungi by Pat O'Reilly

Left to their own and the weather's devices, sand dunes are dynamic systems. New dunes are formed by sand being blown in from the shore at low tide, and the sand on the dunes behind these embryonic dunes is also continuously moved and re-shaped by the wind. In recent years it was thought desirable that our sand dunes should be stablised, making them a less unpredictable force; that is because unstable dune systems can swallow up boardwalks, tracks, roads and even buildings in a remarkably short period of time during stormy weather conditions. As a result the proportion of mobile dunes in our sand dune systems has decreased, according to Countryside Council for Wales reports, from about 70% just 60 years ago to just 6% or so today. Bare sand habitats now form a mere 1.7% of the total area of Wales's sand dunes.

The rare Fen Orchid (Liparis loeselii) is one of the species being pushed towards extinction by over-vegetated dunes

The stabilisation of the dunes was brought about by a number of factors. Coastal developments such as residential homes, holiday parks and sea defences are thought to have had a considerable impact, as also did the deliberate introduction of specialist stabilising plants - Marram Grass for instance -which quickly establishes itself and puts down long and powerful roots. Once Marram Grass takes hold and the dunes become immobile, it is not long before other plants are also able to colonise these areas so that species that can survive only in the mobile dunes are soon crowded out by competition from these newcomers. In time the decaying matter from the new plants affects the purity of the sand, which eventually comes to more closely resemble soil; this in turn, encourages the growth of even more rank plants and shrubs.

In the case of Newborough Warren on the island of Anglesey in North Wales, the colonisation by Marram Grass in the area was so successful that the nearby villagers made a living from harvesting it for use in what became a thriving weaving industry.

Below: Dunes sculpted by the wind at Morfa Harlech NNR

What people had failed to understand was the vital importance of these mobile sand habitats on many rare species that cannot exist in the more stable and overgrown dunes.

We can begin to get an idea of the importance of Wales's sand dune habitats by considering the high level of conservation designations. Of the 56 dune systems in Wales occupying some 8000 hectares, 31 are SSSIs, 6 are SACs and 9 are National Nature Reserves (Merthyr Mawr, Kenfig, Oxwich, Whiteford Burrows, Stackpole, Ynyslas, Morfa Dyffryn, Morfa Harlech and Newborough Warren). These dune systems support numerous species that are entirely dependent upon the pioneering habitats created by shifting sand: 439 vascular plants, 171 bryophytes, 66 lichens, 289 fungi and 500 (at least) invertebrate species.

What can we do about it?

Tried and tested management techniques for rejuvenating sand dunes include so-called 'beach nourishment' (bringing in sand from other beaches and dumping or pumping it where required), grazing and scrub control, deep ploughing, and the stripping of vegetated turf to expose the sand below. More dramatic interventions which are being employed increasingly both in Wales and on mainland Europe (in Holland in particular) include the reactivation by mechanical means of 'blowouts' - dish-shaped hollows that can be naturally created when winds are strong enough to wrench plants out of the dunes and so mobilise the sand. Using diggers and trucks to remove overgrown turf to expose bare sand has proven to be very successful in Holland, and now a similar scheme is being carried out at Kenfig National Nature Reserve where the dunes have become so overgrown with scrub that they threaten the survival of rare species, notable among which is the Fen Orchid (Liparis loeselii). If successful it is hoped that this same method can be employed in other dune systems around the coast of Wales that also support rare and specialised plants, insects and animals.

Below: The Green Tiger Beetle lives in our sand dunes and needs bare sand for its survival. Picture: Mike McCabe NRW

Kenfig National Nature Reserve in Wales is the final frontier for the Fen Orchid, which has all but disappeared from many of its other sites in the UK - predominantly in the fens of East Anglia. It was known from 8 coastal sites in Wales but has now been lost from 7 of them. The number of plants recorded at Kenfig has declined steadily from around 10,000 in the early 1980s to a mere 159 in 2010. At Kenfig this little orchid grows in the dune slacks - flat areas in between sand dunes which are submerged in rain water during the winter and remain moist throughout the year. Although there are plenty of suitable dune slacks at Kenfig NNR, they are becoming too overgrown with plants that are in competition with the Fen Orchid.

Another factor necessary for this orchid's life strategy is now missing at Kenfig: newly formed dunes and dune slacks. The Fen Orchid is a pioneer, thriving on disturbance, and it can quickly colonise new slacks. The only completely new colonies of Fen Orchids are found in newly formed dune slacks, and it seems that the areas of bare sand found there are a crucial factor for the success of new plants.

The Fen Orchid is probably the best known of the species threatened by the lack of pioneer habitats in our sand dune systems, but there are plenty of others that are similarly endangered; the proposed intervention programme in some of our sand dune systems is a matter of life or death for many of them. The aim is to restore a balance in our sand dune systems so that there will be a minimum of 10% bare sand and at least 30% pioneer habitats.

Below: The male Green Tiger Beetle uses its jaws to hold on to his mate during the mating process. Picture Mike McCabe NRW.

One of the quirky creatures that inhabit our sand dunes is the Green Tiger Beetle (Cicindela campestris). As another species that prefers bare ground, it will certainly benefit from the rejuvenation of the dunes to provide more bare sandy places in which it can live and hunt. This bright iridescent green coloured beetle is a fearsome and agile predator with long legs as well as strong jaws with several teeth; it can move at remarkable speed on the ground to catch its prey - caterpillars, ants and any other small invertebrates within range. This beetle prefers not to fly and will only take off if disturbed, and even then it flies only a short distance - again at great speed.

Green Tiger Beetles breed in summer and lay their eggs separately in tiny burrows. When they hatch, the larvae remain in the burrow during the first winter of their lives; there they lie in wait for unsuspecting insects to fall into their lairs. The larvae grab their prey with jaws every bit as ferocious as those of the adult beetles. As they grow the larvae need to enlarge their burrows to accommodate their increasing size, moulting their skins three times during the process.

Below: A Green Tiger Beetle larva in its 'burrow'. Picture Mike McCabe NRW.

Look out for these fascinating little creatures in the bare sandy parts of our dune systems. Bare ground warms up quickly, and the warmer the Green Tiger Beetle is the better it is at racing to catch its food. If you pick one of these little gems of beetles up to inspect it more closely you may well find out how effective its jaws are: it can give you quite a powerful 'nip' - you have been warned!

The Best Sand Dune Nature Reserves in Wales include:

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Sand dune systems and rare specie in Wales, UK - restoration, remobilisation, rejuvenation and conservation work

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Laura Davies, Kath Hewitt, Julie Creer and Hannah Lee showcase an innovative project to protect Wales' sand dunes.

Sand dunes are wild, iconic landscapes. They are biodiversity hotspots, where carpets of orchids survive alongside songbirds, butterflies and a wide array of endangered insects.

The hills of sand are built by the wind, blown out and built again. Hardy plants begin the sequence of dune formation by the strandline in a process called succession, then high, mobile 'yellow dunes' develop along with wetter areas known as dune slacks and flower-rich dune grassland further inland - a natural mosaic of diverse habitats.

Sand dunes are listed as the habitat most at risk in Europe for biodiversity loss

The dunes of Wales can be explored at all times of year and can be found right along the Welsh coastline. In the north-east are Gronant and Talacre dunes; with the famous Newborough Warren and a host of other dunes dotted along the Anglesey coast. Further south is the iconic Morfa Harlech, overlooked by a castle that once stood by the seafront, Stackpole in Pembrokeshire. Onwards to the Gower Peninsula you will find cliff top or 'perched' dunes and the Oxwich National Nature Reserve, and beyond the expansive dunes of Kenfig and Merthyr Mawr.

Dunes are only found on the narrow strip between land and sea and over the years many have been lost to housing, industry, tourism or farming so now they cover only 0.003% of Wales' land mass. Many dunes are now legally protected but rare wildlife is still disappearing - over the last 80 years, nearly 90% of the open sand has been replaced by dense grass and scrub. The dunes have become overly stabilised and dune sand is no longer able to move freely. Sand dunes are therefore listed as the habitat most at risk in Europe for biodiversity loss.

This change has been caused by factors such as; the planting of marram grass, the introduction of conifer plantations and non-native plant species (often done originally to stabilise the dunes); lack of traditional grazing; a declining grazing rabbit population and nitrogen enrichment due to air pollution.

Active management is now needed to help restore the natural dynamism of sand dunes.
Conservation in action
There are two large sand dune conservation projects currently running. These projects are proactively managing a number of sand dune systems throughout Wales for the benefit of wildlife, people and communities.

First, Sands of LIFE is a major project led by Natural Resources Wales, funded by the European LIFE programme and Welsh Government. The project aims to restore and rejuvenate 10 sand dune sites within 4 Special Areas of Conservation in Wales.

Dynamic Dunescapes is funded by the National Lottery Heritage Fund and the European LIFE fund. The project is a partnership between Natural England, Plantlife, National Trust, Natural Resources Wales and The Wildlife Trusts. The project aims to 7,000 hectares of coastal sand dune across restore 22 sand dune sites across England and 12 in Wales.

Both projects work alongside communities and local partner organisations to deliver large-scale practical restoration work. In addition, Dynamic Dunescapes facilitates training and volunteering on the dunes for visitors and local community groups.

The work required at each sand dune site is different, as each dune system is unique. Prior to the beginning of work, specialist surveys are undertaken to determine what management is appropriate at each location.

To promote the rejuvenation of sand dunes, Dynamic Dunescapes and Sands of LIFE use a range of active management techniques. Turf stripping and re-profiling of the dune landscape achieves the remobilisation of sand, allowing it to move once again. Through the creation of notches (gaps) in the front of the dunes wind is able to transport sand inland, rejuvenating areas of the dunes within and beyond the foredunes.

By digging shallow scrapes in dune slacks (low-lying hollows in the dunes) we can remove dense grasses and organic matter from the surface and expose bare sand. This allows specialist pioneer species (early settling plant species) to re-establish without being outcompeted by more vigorous vegetation. The scraping work can also recreate seasonally wet habitat, which has dried out due to changing land use, forestry and invasive species which absorb water. Excavating close to the underlying water table allows these areas to become wet in winter and spring, making perfect conditions for specialised and rare dune plants such as the Petalwort ( Petalophyllum ralfsii), and a variety of orchids, as well as areas for amphibians to breed.

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In addition, the dunes are being actively managed through the sustainable grazing by livestock and rabbits. Grazers eat in different ways. Cattle use their tongues, wrapping it around plants and pulling them up, while sheep move slowly, nibbling the vegetation down. As well as grazing, rabbits dig and expose bare sand where insects will burrow and pioneer plants will settle . The activities of these animals promote a diversity of plant heights, supporting the recovery of biodiversity in the dunes. The projects have erected new fencing to ensure that the livestock remain safe and rabbits are encouraged by mowing specific areas and creating artificial warrens.

Dunes aren't only a place for wildlife to thrive, but for people to enjoy, exercise and connect with nature, too.

Other work includes cutting scrub, removing invasive alien species and monitoring the recovery of these habitats. Through active management the dunes are being restored and rejuvenated, facilitating the right conditions for dynamic dune processes to occur and creating habitat for rare dune species to thrive. This will increase the resilience of these sand dunes for the future.

Active conservation practices have led to genuine success stories. Protected species such as the Fen Orchid ( Liparis loeselii ) have declined dramatically over the years. Fen Orchid is a very rare type of orchid which grows in dune slacks. The population in Wales, which used to exceed 10,000 plants, had dwindled to such an extent that it had become extinct in all but one of its sites, Kenfig National Nature Reserve, near Bridgend. However, the Fen Orchid has been re-discovered this summer at another South Wales site, Laugharne-Pendine Burrows, due to years of carefully planned conservation management b y the Sands of LIFE project and the Ministry of Defence. It was last recorded at this site nearly 20 years ago and this recent discovery shows how successful active management is.

Dunes aren't only a place for wildlife to thrive, but for people to enjoy, exercise and connect with nature, too. The conservation of nature and our connection to it go hand in hand in achieving ambitious restoration goals. Sand dunes might be considered a mysterious part of our landscape, usually passed through on our way to the beach. But these habitats hold vast secrets, just waiting to be discovered.

Working closely with local communities and visitors in Wales are core aims of both the Dynamic Dunescapes and Sands of LIFE projects. This involves creating opportunities for people to explore the dunes, to learn about the special wildlife of the dunes and sharing their own stories and expertise. Throughout the year, across all the project sites there are guided walks focusing on different points of interest on the dune, from bees to plants and fungi to beetles.

In addition to guided walks, a range of more hands-on volunteering activities are also offered, such as the Dynamic Dunescapes citizen science project. Focused on monitoring the ongoing conservation work, volunteers throughout Wales have been training and taking part in vegetation, dune profile, and photographic monitoring at the various restoration sites. The data collected will help guide future management. Through collaboration with local partners, Dynamic Dunescapes facilitates training and support for volunteers interested in monitoring reptiles, butterflies, bumblebees and other coastal species in the dunes.

It's also possible to explore the dunes from the comfort of your own sofa, through online events focused on coastal species and the colourful history of sand dunes to short videos about ongoing work and the wildlife of the dunes such as these from the and

So if you're feeling inspired, next time you visit the beach, pause in the dunes, surrounded by plants and listen to the song of skylarks, linnet and stone chats as they fly overhead. For ideas for activities or to learn more about the ongoing conservation actions, visit the project websites: Dunescapes ; Sands of LIFE
All articles published on the welsh agenda are subject to IWA's disclaimer.

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The Sand Dunes of Wales - Conserving and Exploring our Hidden Gems - Institute of Welsh Affairs

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Laura Davies, Kath Hewitt, Julie Creer and Hannah Lee showcase an innovative project to protect Wales' sand dunes.

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Our Gems in the Dunes project, part of the national Back from the Brink programme, is helping endangered sand dune eco-systems, enabling some of Britain's rarest wildlife to return to the Sefton Coast.
Wildlife native to the Sefton dunes include six key species: natterjack toads - unmistakeable on a calm spring evening in the dunes with their distinctive call that can be heard a mile away; sand lizards - possibly one of the hardest creatures to spot, despite their vivid lime green appearance; while the northern dune tiger beetle will leave you for dust as one of the fastest insects on the planet! Miniature plants such as petalwort resemble little gem lettuce; sea bryum and matted bryum leaves carpet the sand, looking like velvet - thus the Velvet Trail in Birkdale, so named by the Victorians. Life however is tough for these species, and getting tougher as their habitat disappears, making the project key to its survival.

used to provide a balanced mix of vegetation, however due to environmental and man-made factors that has all changed. The vast majority of the dune system has been overtaken by invasive vegetation, in particular sea buckthorn and Japanese rose, choking the typical plant species, on which rare reptiles and amphibians depend on to thrive. If allowed to continue it won't be long before many rare plants and animals disappear from the dunes for good.

The Gems in the Dunes team, based at Ainsdale Discovery Centre in Southport, is working with local landowners to slow down and ultimately reverse the process of over vegetation by rebalancing the landscape. Contractors have removed large areas of scrub from the dunes at Altcar Training Camp as well as the National Nature Reserves at Cabin Hill and Ainsdale. The scrub forms dense impenetrable stands that prevent animals from moving freely around, and can lead to problems of isolation. It also creates shade over the sand - no good when you need the warm sand to bask on, hunt or lay your eggs in as do sand lizards and tiger beetles. With the removal of the scrub, typical low growing ground cover plants such as restharrow, grass of parnasus, sea holly and many orchids, can thrive. A healthy variety of plants attracts an abundance of insects, food for the lizards, toads and beetles.

"Changes in weather patterns has seen vegetation flourish in dune pools too - not a good thing for many dune specialist species. We have worked with contractors and landowners to create new pools, rejuvenate of old ones, and improve connectivity between them. This helps avoid the natterjack toads becoming isolated. Petalwort, sea bryum and matted bryum have a better chance of survival too, on the sandy pool margins without too many other plants to compete with." Says project Manager, Fiona Sunners.

Amphibian and Reptile Conservation are one of the seven partners working with Natural England supported by National Lottery Heritage Fund. This funding helping 19 wildlife projects across England that are a part of the Back from the Brink programme, to improve the fortunes of over 200 of the rarest species across England.

Help safeguard the future of natterjack toads in the UK, where they are threatened by habitat loss.

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Find out more about how our Gems in the Dunes project is working to save six of the Sefton sand dunes' most threatened species

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The coevolution of topography and vegetation in response to both physical and ecological factors

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Frosini, Lardicci & Balestri - 2012

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Silvia Frosini,

Claudio Lardicci,

Elena Balestri

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Abstract

Coastal dune plants are subjected to natural multiple stresses and vulnerable to global change. Some changes associated with global change could interact in their effects on vegetation. As vegetation plays a fundamental role in building and stabilizing dune systems, effective coastal habitat management requires a better understanding of the combined effects of such changes on plant populations. A manipulative experiment was conducted along a Mediterranean dune system to examine the individual and combined effects of increased sediment accretion (burial) and nitrogen enrichment associated with predicted global change on the performance of young clones of Sporobolus virginicus, a widespread dune stabilizing species. Increased burial severity resulted in the production of taller but thinner shoots, while nutrient enrichment stimulated rhizome production. Nutrient enrichment increased total plant biomass up to moderate burial levels (50% of plant height), but it had not effect at the highest burial level (100% of plant height). The effects of such factors on total biomass, shoot biomass and branching were influenced by spatial variation in natural factors at the scale of hundreds of metres. These results indicate that the effects of burial and nutrient enrichment on plant performance were not independent. Their combined effects may not be predicted by knowing the individual effects, at least under the study conditions. Under global change scenarios, increased nutrient input could alleviate nutrient stress in S. virginicus, enhancing clonal expansion and productivity, but this benefit could be offset by increased sand accretion levels equal or exceeding 100% of plant height. Depletion of stored reserves for emerging from sand could increase plant vulnerability to other stresses in the long-term. The results emphasize the need to incorporate statistical designs for detecting non-independent effects of multiple changes and adequate spatial replication in future works to anticipate the impact of global change on dune ecosystem functioning.

Citation: Frosini S, Lardicci C, Balestri E (2012) Global Change and Response of Coastal Dune Plants to the Combined Effects of Increased Sand Accretion (Burial) and Nutrient Availability. PLoS ONE 7(10): e47561. https://doi.org/10.1371/journal.pone.0047561

Editor: Anna Traveset, Institut Mediterrani d'Estudis Avançats (CSIC/UIB), Spain

Received: August 1, 2012; Accepted: September 18, 2012; Published: October 15, 2012

Copyright: © Frosini et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This work was a part of the Ph.D. thesis of S. Frosini supported by a fellowship from the University of Pisa. The study was partially funded by Solvay Chimica Italia S.p.A. of Rosignano Solvay ( www.solvay.it). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have read the journal's policy and have the following conflicts: CL receives grant/research support from Solvay Chimica Italia S.p.A. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials. All other authors have nothing to disclose.

Introduction

Coastal sand dunes, along with the numerous valuable goods and services they provide [1]-[3], are threatened worldwide by both anthropogenic activities and climate change [4]-[8]. Physical and chemical changes associated with global change will potentially affect dune ecosystem structure and functioning in the coming centuries [7]-[12]. Dune plants play a fundamental role in determining the form, function and stability of dune systems [13]. Therefore, understanding and anticipating the response of individual plant species to abiotic changes is essential for developing effective coastal management and conservation strategies. However, this is problematic because in nature dune plants are subjected simultaneously to a variety of environmental stresses [14]-[19]. Although numerous studies have addressed dune plant adaptation to individual environmental stresses [20], [21], [17], [22], [23], [18], little is still known about how plants integrate the signals associated with concurrent stresses and adjust their growth accordingly. Climate-induced changes are expected to enhance the magnitude and frequency of existing natural and anthropogenic stress factors to levels that could exceed dune plant tolerance. Some changes could interact (synergically or antagonistically) in their effects, making it complex to predict the net effect on vegetation [24].

For example, alteration of global nutrient cycles due to the use of fertilizers and increased atmospheric deposition will enhance the inputs of nutrients, particularly nitrogen (N) and phosphorus (P) [25]-[27]. Predictions indicate that by 2050, nitrogen deposition may double, with some regions of the world reaching 50 kg N ha −1 yr −1 [28], [25]. The availability of N in soils plays a fundamental role in influencing plant community composition and stability [29]. Increased N deposition will likely be one of the greater drivers of plant biodiversity loss at the global scale over the coming century [24], [25]. Coastal sand dunes are nutrient poor habitats and plant productivity has been found to be limited by both N and P [30], [16]. Studies have shown that increased nutrient inputs would favour the growth of some species (tall grass species, in particular) while would make others more vulnerable to disturbances and stresses [30]-[33], [23]. However, it is unclear whether increased atmospheric N deposition alone can induce encroachment by dune grasses or whether other factors are involved [30], [23]. On the other hand, changes in atmospheric circulation will increase the frequency of extreme wind events, leading to more frequent episodes of sand accretion in some areas [34]-[36]. Burial by wind-deposited sand is one of the major physical stresses that can alter dune community composition, distribution and abundance [14], [37], [15], [16]. There is large variation in the degree of adaptation to burial among dune species. Substantial variation also occurs within a species in function of life history stage, season and burial severity, in terms of depth relative to the height of plants [14]-[16] and frequency. Many plant species are able to emerge from low or moderate levels of burial (less than 50% of plant height) by elongating shoots (positive growth response), but only few species (i.e., Ammophila spp.) are able to withstand deeper burial [14]-[16], [38]. Other species are unaffected (neutral growth response) or inhibited (negative growth response) by burial [14]-[16], [37], [38]. However, recurrent frequent shallow burial events can be more damaging than a single event of greater magnitude [39], and juveniles may be especially sensitive to such events [40]. Therefore, species intolerant to recurrent shallow burial events are expected to be prevented from occupying mobile dunes and spatially replaced by more tolerant species under wind pattern change scenarios. However, there is still no general consensus on the physiological mechanisms behind burial growth response [38]. Potential mechanisms include shifts in resource (such as biomass and nutrients) allocation from below-ground to above-ground components, remobilization of stored resources, changes in photosynthetic rate or other attributes, and reduction of the dry mass cost of producing new leaves and elongating stems [14]-[16], [41]. More recent studies have shown that the ability of mobile dune species to respond to burial may largely depend upon the availability of nutrients [20], [22]. However, severe sand deposition episodes may drastically modify physical or chemical micro-environment characteristics and also favour the activity of anaerobic microorganisms [14], [30], potentially reducing or preventing plant nutrient uptake. The possible interaction between nutrient availability and burial implies that their net effect on a given plant species may be larger than, or smaller, than the expected individual effects. To our knowledge, very few studies were designed to test in the field the potential non-independent effects of more than one factor on coastal dune vegetation in relation to global change [23].

In this study we investigated the response of young clones of Sporobolus virginicus Kunth, a pioneer dune herbaceous species [42]-[43], to the individual and combined effects of increased repeated burial levels and N enrichment to gain more insights into how mobile dune plants will change in the future. Sporobolus virginicus was chosen as model because of its worldwide distribution and fundamental role in stabilizing mobile dune substrates [43]-[45]. The burial tolerance limit of this species has not been investigated yet. We hypothesized that the effects of the two investigated factors on plant performance would be non-additive (interacting). Specifically, we expected that plant growth might be nutrient limited, and enhanced nutrient availability might stimulate plant productivity alleviating physiological stress under increased burial conditions. As an alternative, increased nutrient input might have no positive effect on plant growth under increased burial conditions because of alterations of sediment properties or metabolic shift from an energy-producing to an energy-consuming state [16]. Since in coastal habitats a number of factors, including topographic features, edaphic conditions and resource distribution, can vary at the scale of microhabitat [8], [46]-[49], the effects of the experimental factors were tested across different spatial scales, from tens to hundreds of meters, along a Mediterranean dune system. To our knowledge, no previous field studies have explicitly assessed whether the response of a species to abiotic factors was consistent in space along its distribution zone (horizontally) within a dune system.

Materials and Methods

Ethics Approval

All necessary permits were obtained for the described field studies. The study site belongs to Rosignano Marittimo Municipality which issued the permission for all our field studies. The species is not protected in Italy, but the habitat has a priority status in Europe (Habitat Directive 92/43/EEC). In field studies we tried our best not to damage seedlings or individuals.

Net changes in sand accumulation (cm) relative to erosion pins (n = 24) placed along a transect parallel to the coastline at the study dune system. Data were recorded weekly from 13 April to 29 August 2010. Bars represent ± SE.

Study Species

Sporobolus virginicus (Poaceae) is a perennial, herbaceous clonal species widely distributed along tropical and subtropical lagoon, sand beaches and estuaries [42]. The tolerance of this species to waterlogging and salinity can account for exploitation of a wide range of coastal environments [43], [50]. In Italy, the presence of this species has been reported only recently because it was retained as a distinct species and referred to as Sporobolus pungens Schreber Kunth [51]. Clones form horizontal rhizomes that produce branched or solitary ascending culms and adventitious roots at each node. Rhizome connections and roots form large networks which efficiently stabilize substrates and initiate the recovery of mobile dunes following disturbance [42]. In the Mediterranean dunes, the vegetative growth of this species occurs from late winter (February) to the end of autumn, and the reproductive season generally lasts from May to September [52]. Flowers consist of spike-like hermaphroditic panicles, 2-10 cm long. Despite S. virginicus can produce seeds [53], recruitment from seed is considered rare in nature [54].

Study Locality and Plant Material Preparation

The study was conducted on the coastline of Rosignano Solvay in the north-western Italy (43°22′43.10′′N, 10°26′15.77′′E). The coastline is characterized by a mobile dune system (2.5 km long) that runs parallel to the shoreline; the height of dunes varies from 1.0 to 8.5 m from the 0 m water level. Winds are predominantly from the south- and south-west during the winter and from northwest in the summer, favouring a net inshore movement of sand. Available data indicated that the frequency of extreme winds in summer considerably increased during the past decades [55]. The climate is typical Mediterranean: the mean daily temperature of the coldest month (January) is 5°C, while that of the warmest month (July) is 25°C (data from local meteorological stations). The substrate of beach and mobile dunes is fine strongly alkaline sand (98.7%, silt 0.4%; clay 0.9%; pH >8.3), rich in calcium carbonate (CaCO3, 86.59%) [56]. Dune system is dominated by Ammophila arenaria (L.) Link (European beachgrass) and Elymus farctus (Viv.) Runemark ex Melderis. S. virginicus is abundant on the upper beach and first mobile dune ridge where it forms large monospecific patches parallel to the shoreline. The net sand accretion rate at the study dune system over the study period was estimated by monitoring changes in the level of sand deposition relative to erosion pins (24 pins) randomly placed along a transect parallel to the shoreline. The height of pins was weekly measured with an accuracy of 1-2 mm.

Because seeds of S. virginicus are rare [53] and defining individual clones in nature is difficult, prior to the experiment (October 2009) clones were produced in a nursery by vegetative propagation from rhizome fragments (with two-nodes and about 8 cm in length) collected at the edge of established patches at the study site. These fragments were rooted into pots (30 cm depth and 10 cm diameter) containing a 1∶1 (v/v) mixture of beach sand and potting compost, and maintained outdoor. In April 2010, rooted plants were extracted from sediment for morphological measurements (rhizome length, number of shoots, number of branches and maximum shoot height). This material was representative of plants established in nature from clonal fragments generated during autumn-winter storms. Understanding the ability of such plants to withstand incoming environmental changes is critical because of their major role in expanding populations and recovery after disturbance [57], [58]. To remove the possible effect of different clone size, similar-sized plants (96 plants) were selected and transported to the study system. Two areas, separated by hundreds of meters, were randomly chosen along the dune system and within each area two sites, ten of meters apart, placed on the first dune ridge were selected at random. The sites (2-3 m wide dune stretches) had an elevation of 1.2-1.5 m from the 0 m water level, and their distance from the shoreline was ca. 80 m. Plants (24 plants) were individually transplanted in random positions on zones of bare substrate within a natural S. virginicus population within each site. Plants were separated from each other by at least 0.5 m to avoid possible contamination between treatments. Three plants, dead soon after planting, were substituted with plants maintained in the nursery as reserve. The study dune tract was fenced in attempt to prevent anthropogenic interference.

Experimental Design

After acclimation (late May 2010) to local environmental conditions, plants growing in each site were randomly assigned to one of six treatments: moderate sand burial resulting in the cover of 50% of shoot height (partial burial, PB/N-), high sand burial resulting in 100% cover of shoot height (complete burial, CB/N-), no sand burial and nutrient enrichment (NB/N+), partial sand burial and nutrient enrichment (PB/N+), complete sand burial and nutrient enrichment (CB/N+), no sand burial and no nutrient enrichment (ambient conditions, NB/N-). Before the start of the experiment, rhizome length, number of shoots, number of branches and maximum shoot height of plants were measured to test whether the plants assigned to different treatments did not differ significantly from each other in morphology and size. A preliminary study has shown that the mean annual net sand accretion recorded at the study site corresponded to a burial of 50% of shoot height (about 5 cm; personal observation). Woody frames (30×30 cm in size) were placed around each plant and filled with sand to maintain the assigned burial level. To elevate nitrogen concentration and reduce leaching, a single dose of a commercially available fertilizer (COMPO, K+S Agricoltura Spa, g/g ratio N-P-K 13-6-9) formulated for a 3-month complete element release was inserted into the sediment. Treatment N is equal to a dose of 14 kg N ha −1, and treatment P to 6.6 Kg P ha −1. The N dose is equivalent to the deposition estimates (15-20 kg N ha −1 year −1) predicted for the 2050 in the Mediterranean basin [28], [25]. In addition, two treatments, in which empty frames were placed around plants were used to control for possible artifact effect: artifact control and no nutrient enrichment (AC/N-) and artefact and nutrient enrichment (AC/N+). There were three replicates for each treatment.

Plants were monitored at weekly intervals until the end of the experiment (August 2010). At each census, plants were carefully inspected for herbivore damage because of its potential influence on plant growth [59], and the height of newly produced shoot tissue was measured. As the experiment was trying to simulate recurrent burial summer events, plants were reburied weekly to the experimental originally attributed burial level. The sand used for burial treatments during the course of the experiment was collected to a depth of maximum 10 cm closely to the treated plants; it was sieved to remove propagules and extraneous material prior to the use.

At the end of the experiment, the number of plants that had recovered from burial was recorded. The root system of surviving plants was gently excavated to remove plants from the substrate. Plants were transported to the laboratory where morphological characteristics that were expected to be affected by the investigated factors on the basis of available literature (horizontal rhizome length, number of vertical shoots, maximum shoot height, number of branches, number and length of vertical internodes measured on the highest shoot, and the number of reproductive shoots per plant) [20], [14]-[16], [22], [41] were recorded. Plants were then separated into shoots, roots and rhizomes and dried at 60°C until they reached constant weight (dry weight, DW) to determine the respective biomasses. In addition, to investigate plant response in terms of resource allocation and efficiency of production, root to shoot ratio and specific shoot height (SSH) were calculated. Root to shoot ratio, which reflects the differential investment of photosynthates between the above-ground and below-ground organs [60], was calculated by dividing root by shoot biomass (g g −1 DW). Specific shoot height, which is considered an indicator of the dry mass cost of producing shoots [41], was calculated as the ratio between total shoot height and shoot dry weight (cm g −1 DW).

Data Analysis

Data on morphological and growth variables were analysed separately for the time period before the treatments were initiated (May 2010) and for the time period following the treatments (August 2010). Initial data were analysed throughout multivariate analysis of variance by permutation, PERMANOVA [61], according to a randomized ANOVA design that included the orthogonal factors area (two levels, random) and treatment assignation (eight levels, random), and the factor site (two levels, random) nested within area and orthogonal to treatment assignation. Final data were analysed using PERMANOVA according to mixed model ANOVA design that included the orthogonal factors area (two levels, random), burial (four levels, fixed) and nutrient (two levels, fixed), and the factor site (two levels, random) nested within area and orthogonal to burial and nutrient. Because of the loss of two plants in one area, unbalanced PERMANOVA with type III sums of squares was performed [62]. Since significant effects were detected in PERMANOVA, separate ANOVAs were performed for all investigated variables according to the same model. Separate ANOVAs were also conducted on total plant biomass, root to shoot ratio and specific shoot height. Missing replicates were substituted with the mean of that particular combination of treatments and two degrees of freedom were subtracted from the total degrees of freedom of the residual mean square [63].

Prior to PERMANOVA, data were normalized and dissimilarities calculated as Euclidean distances. Significance levels were calculated from 9999 permutations of the residuals under the reduced model. Whenever possible, post hoc pooling of mixed terms of the model was performed to increase analysis power [64]. When a significant effect was found, post hoc pair-wise comparisons (PERMANOVA t statistic and 999 permutations) were used to distinguish between means. For some terms, there were not enough permutable units to get a reasonable test by permutation, so P-values were obtained using a Monte Carlo random sample from the asymptotic permutation distribution [62]. Statistically significant terms were checked for differences in multivariate group dispersion with the permutational analysis of multivariate dispersions (PERMDISP) [65]; pair-wise comparisons of multivariate dispersion were also performed between all couples of groups. Prior to performing ANOVAs, data were tested for normality and homoscedasticy, and transformed if necessary. Whenever data transformation failed to achieve homogeneity of variances, the analysis was performed on untransformed data with α = 0.01 [64]. When significant effects were detected, means were compared through the Student-Newman-Keuls (SNK) test [64]. As for the multivariate analysis, post hoc pooling of mixed interaction term was applied whenever possible.

PERMANOVA and PERMDISP were run through PRIMER v6 (Primer-E Ltd., Plymouth) [66] with PERMANOVA add-on software, while statistical software R version 2.12.2 [67] and R package "GAD" [68] were used for ANOVAs.

Results

Before applying the treatments, the plants randomly assigned to different treatments were of equal age (six months) and similar size (see Table S1). They had on average 1.5 (±0.1 SE) shoots and 2.7 (±0.1) branches; shoot height was on average 10 (±0.2) cm and the horizontal rhizome was 8.7 (±0.2) cm long. Two of the 96 transplanted individuals disappeared during the study period because of unknown factors. At the end the experiment, survived plants had produced at least one new shoot each. No inflorescences were observed during the study period and no sign of herbivore damage was detected in plants. All plants exposed to increased burial were emerged above the sand surface. The mean height of sand deposed on plants exposed to partial burial over the course of the experiment was 8 cm (±0.4) while the height of sand deposed on plants exposed to complete burial was 19.2 cm (±1.6). These values were higher compared to the sand deposition level experienced by plants grown at ambient conditions over the study period along the dune system ( Fig. 1). No traces of fertilizer were detected in the soil at plant harvesting, indicating that the release of nutrients was complete in the experimental period.

A significant interaction between nutrient availability and burial on whole plant response was detected ( Table S2). Overall, plants grown under nutrient enhanced conditions differed from those grown under nutrient ambient conditions, and partially buried plants differed from completely buried plants but only when grown under nutrient enhanced conditions ( Table S3). No difference in multivariate dispersion among significantly differing groups was detected (pair-wise PERMDISP test: unfertilized vs. fertilized for unburied plants, t = 0.99, P = 0.361; fertilized and completely buried vs. fertilized and partially buried plants, t = 1.08, P = 0.373), indicating that the effects reported above were effectively due to investigated factors, and not to a different multivariate dispersion among groups. A significant interaction between nutrient supply and area was also detected (fertilized plants differed from unfertilized ones only in one of the two areas, Table S3), but this could be due to different multivariate dispersion of the groups (PERMDISP test for unfertilized vs. fertilized plants in area 1, t = 3.46, P  = 0.006) rather than to the investigated factors.

The results from separate ANOVAs showed that for three out of the nine investigated morphological and growth characteristics, the effect of burial and nutrient availability was additive (i.e., no significant interaction occurred), while for one variable it was non-additive (significant interaction occurred). Burial alone significantly affected shoot height and shoot internodes length ( Table 1). Plants grown under completely buried conditions had on average taller shoots (ca. 35-40%) than those grown under ambient burial conditions, while those grown under partially buried conditions had an intermediate height ( Fig. 2A-D). Shoot internodes of completely buried plants were significantly longer (about. 20%) than those of partially buried plants that in turn were about 15-20% longer than those at ambient burial conditions ( Table 1, Fig. 2E-H). Instead, nutrient availability alone significantly affected rhizome length ( Table 1). The rhizome of plants grown under enhanced nutrient conditions was about 30% longer compared to that of plants grown under ambient nutrient conditions ( Fig. 3E-H). Burial and nutrient availability in combination affected rhizome biomass. Nutrient addition resulted in a threefold increase in rhizome biomass but only under ambient burial conditions ( Fig. 4E-H; Table 1). Results also indicated a significant interaction between nutrient supply and area for two variables, shoot biomass and number of branches. Both shoot biomass and number of branches increased under enhanced nutrient conditions, but only in one of the two areas (area 1, Figs. 3I-L and 4A-D; Table 1). For this latter variable, a significant effect of site was also observed ( Fig. 4A-D; Table 1). Finally, for the remaining three variables, number of vertical internodes, number of shoots and root biomass, no significant effect of the investigated factors, alone or in combination, was observed ( Figs. 2I-L, 3A-D and 4I-L; Table 1).

Total plant biomass was significantly affected by the interaction between burial and nutrient availability ( Table 2). When grown under enhanced nutrient conditions, the biomass of plants increased significantly as compared to that of plants grown under ambient nutrient conditions, except when plants were completely buried. Under enhanced nutrient conditions, the total biomass of completely buried plants was about half of that of plants partially buried or grown at ambient burial conditions ( Fig. 5A-D). Significant interactions between area and burial, and between area and nutrient supply, were also detected ( Table 2). The biomass produced by plants grown at ambient burial conditions was greater than that of plants subjected to partial burial, and the biomass of these latter was in turn greater than that of plants grown under complete burial but only in one of the two areas (area 2). Significant differences in the biomass of plants grown at ambient burial conditions between areas were also found. In both the areas, the biomass of fertilized plants was greater than that of unfertilized ones. The biomass of unfertilized plants was higher in the area 2 than in area 1, while the opposite pattern was found for fertilized plants ( Fig. 5A-D). Specific shoot height was significantly influenced by burial alone, and increased with the increase of the severity of burial, from 99.23 (±14.01) cm g −1 DW at ambient conditions to 198.6 (±22.62) cm g −1 DW under completely buried conditions, ( Fig. 5E-H; Table 2). Finally, the root to shoot ratio was much less than 1 (ranging from 0.22±0.003 to 0.28±0.004 g g −1 DW at the four sites) indicating that a substantial larger portion of biomass was concentrated above-ground ( Fig. 5I-L). No significant differences were detected for this variable among treatments, indicating that individuals did not change their biomass allocation pattern in response to any of the investigated factors ( Table 2).

Discussion

Burial by sand has been assumed to be a major environmental stress reducing plant performance in dune species, especially in their early life history stages [14]-[16]. Our results showed that young clones of S. virginicus were able to recover from increased sand accretion levels that corresponded to about four times the mean maximum burial depth they naturally experienced over the study period, by elongating internodes in vertical shoots regardless of nutrient availability. This indicates that this species possesses an inherent ability to respond to burial that is consistent with its role of primary colonizer of dune areas of high sand movement [42]. Contrasting results emerged from previous studies on the mechanisms underlying compensatory shoot growth in response to burial in dune plants [20], [22], [41], [38]. A number of studies reported evidence of shifts in resources from below-to above ground plant parts [40], [69], while other studies failed to detect it [70] or indicated that shifts were only possible at low or moderate burial levels (up to 66% of plant height) [38]. In the current study, stimulation of shoot elongation by burial might not be attributed to an increased biomass investment in the above-ground structures, as the root to shoot ratio was unaffected by burial. Instead, the increased specific shoot height indicates that the resources required for emerging from sand were obtained by reducing shoot production costs (i.e., more shoot length was produced with the same amount of biomass) and remobilizing resources from buried shoot tissue. Such response, which has been rarely observed in dune plants [41], could be adaptive, as it minimises nutrient use but maximises shoot growth, enabling the species to survive on mobile substrate under nutrient-limited conditions. However, depletion of stored reserves and production of thinner shoots due prolonged burial events may increase the vulnerability of plants to other abiotic stresses.

Previous studies demonstrated that nutrient inputs from atmospheric deposition favour the growth of graminoids and nitrophilous species, resulting in perturbation of competitive hierarchy among dune plant species with consequent loss of diversity and conservation habitat value [30]-[32], [23]. Here, nutrient addition alone resulted in increased rhizome production in S. virginicus, confirming our hypothesis that the species growth was nutrient limited under ambient conditions. Similarly to burial, increased nutrient availability did not induce shifts in biomass allocation from below- to above-ground components. This is not in agreement to that previously observed in most dune species [32], [71], [37]. Thus, S. virginicus can be considered as "form-conservative", i.e., the form and the allocation of biomass of a plant of given size is the same irrespective of the nutrient microenvironment [72].

According to our prediction, the effects of nutrient enrichment and increased burial on total biomass production were non-independent. However, while total biomass increased in response to nutrient enrichment under partially buried conditions and at ambient conditions, no consistent biomass increase was found under completely burial conditions. Consequently, increased nutrient availability was ineffective in ameliorating plant stress under complete burial. This suggests that burial-driven alterations in the sediment micro-environment reduced the availability of nutrients or the uptake efficiency in plants [14], [30]. Another explanation might be the shift observed in completely buried plants from an energy-producing to an energy-consuming state [16].

Finally, the variability in the response of S. virginicus to nutrient availability and burial observed at small spatial scales (hundreds of metres) along the study dune system for some growth and architecture variables indicates that local natural factors, such as dune topography and light intensity [8], [46]-[49], might have interacted with the manipulated factors. Although a number of studies indicated that abiotic factors may vary at small spatial scales, not only across (transversally) but also along the shore (horizontally) on a dune system [46]-[48], the majority of the previous experimental studies on dune plant response to abiotic factors lacked of spatial replication, making it difficult to generalize their results.

In conclusion, the present study suggests that increased nutrient availability and burial severity may interact in their effects on dune plant performance, thus their combined effects may be not predicted by knowing the individual effects. According to recent models [28], [25], current N atmospheric deposition rate at the study site was about 5 kg N ha −1 y −1. Total N input (current plus experimentally imposed) was about 15.5 kg ha −1 in three months, a value close to the annual deposition level predicted for the 2050 in the Mediterranean basin [28], [25], and also within the range of the critical loads (10-20 kg ha −1 yr −1) for European foredune systems [23], [30]-[33]. We therefore expect the changes in atmospheric N deposition in the coming decades could alleviate nutrient stress in newly regenerated clones of S. virginicus enabling them to produce longer rhizomes and exploit a larger number of nutrient-rich patches or pulses on mobile dunes, resulting in higher plant cover. However, in areas with sand accretion levels equal or exceeding plant height the benefits of increasing nutrient input could be offset by burial stress, and prolonged burial exposure could reduce plant performance. Further studies on the effects of multiple factors on different species that could potentially outcompete S. virginicus on mobile dunes are needed to improve predictions about the possible consequences for population expansion in the long-term. The results also emphasize the need to incorporate statistical designs for detecting interactions between stressors, non-independent effects of multiple stresses and adequate spatial replication in future works. A better understanding of how dune plants will respond to the cumulative effects of abiotic changes is critical to establish effective conservation approaches and restoration actions in order to mitigate the effects of incoming global change on coastal dune structure and functioning.

Supporting Information

PERMANOVA on Euclidean distances of plants assigned to different treatments replicated in two sites within two areas selected at random along the study dune system at the beginning of the experiment (May 2010).
https://doi.org/10.1371/journal.pone.0047561.s001
(DOC)

PERMANOVA on Euclidean distances of plants subjected to different treatments replicated in two sites within two areas selected at random along the study dune system at the end of the experiment (August 2010).
https://doi.org/10.1371/journal.pone.0047561.s002
(DOC)

Acknowledgments

The authors thank Flavia Vallerini, Giada Russo, Marta Volpi, Erika Seghesio, Domenico Ciorciaro, Giulia Vagnoli, Giulia Cirilli and Amedeo Ciccocioppo for technical support, and the station of the Corpo Forestale dello Stato of Cecina Marina (Livorno, Italy) for providing facilities during the phase of plant production. The authors are also grateful to the Editor Anna Traveset and two reviewers for valuable suggestions and comments that helped improve and clarify earlier versions of the manuscript.

Author Contributions

Conceived and designed the experiments: SF EB CL. Performed the experiments: SF EB. Analyzed the data: SF EB CL. Contributed reagents/materials/analysis tools: CL. Wrote the paper: SF EB CL.

# data[].attributes.attachment_link.title
Global Change and Response of Coastal Dune Plants to the Combined Effects of Increased Sand Accretion (Burial) and Nutrient Availability

# data[].attributes.attachment_link.description
Coastal dune plants are subjected to natural multiple stresses and vulnerable to global change. Some changes associated with global change could interact in their effects on vegetation. As vegetation plays a fundamental role in building and stabilizing dune systems, effective coastal habitat management requires a better understanding of the combined effects of such changes on plant populations.

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Carboni, Carranza and Acosta - 2009

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Tuft forming, 15 to 80 cm tall usually with creeping rhizomes and surface runners. Basal leaves and those of runners are all bristle like and up to 40 cm long with groove on upper side. Those of the flowering stems are flat when fresh 0.5 to 3 mm wide.

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Learn about Sea Couch Grass, a perennial species of grass common in coastal habitats. Find information about growing and caring for Sea Couch Grass, as well as other helpful tips for this plant.

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Soil and... Sand Dunes? - Dynamic Dunescapes

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Soils play an important role in sand dune life cycles and support many threatened species - find out more this World Soil Day!

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Abstract

More structurally complex vegetation was associated with a higher site occupancy for two species. Two species had higher site occupancies where natural and urban hinterland types occurred. Coastal dunes represent habitat for wildlife yet are chronically understudied and are threatened by anthropogenically driven processes from their landward and seaward margins. We deployed 93 downward-facing cameras along the coastal dunes of Venus Bay, Victoria, Australia, to examine the influence of natural and anthropogenic processes on the occurrence of vertebrate fauna. Of the 32 species identified, ten had sufficient data for single-species, single-season occupancy modelling. Four species occurred ubiquitously in dunes and can be regarded as generalists within the dunescape. For six species, site occupancy increased with increasing distance from the coast. Areas with less modified dune trended towards lower species site occupancy for five species Normalised Difference Vegetation Index (NDVI) featured in one species model, with a weak negative trend of vegetation productivity on occurrence. We confirm that coastal dunes represent a diverse faunal ecosystem, with species varying in their occurrence and the processes (from the seaward and hinterland margins, natural and anthropogenic) which influence it. .

Introduction

Coastal dunes are distinct landscape features, harbouring important refugia for wildlife in human-dominated coastscapes, but which are chronically understudied with respect to their role as habitat for wildlife (Rendall et al., 2019; Schlacher et al., 2014). They are neither strictly marine nor terrestrial ecosystems but are transitional between marine and terrestrial domains (Jackson et al., 2013; Lithgow et al., 2013; McLachlan, 1991). The few available studies suggest coastal dunes may represent highly diverse, unique ecosystems, supporting equally diverse communities of native and introduced flora and fauna (Ben-Ami and Ramp, 2013; Brown et al., 1996; Di Stefano et al., 2009; Fischer et al., 2019, 2021; Rendall et al., 2019; Swan et al., 2008). In many coastal dunes, vegetation remains uncleared, in contrast to their hinterlands, which have often been radically altered by humans (Ben-Ami and Ramp, 2013; Bird et al., 2020; Defeo et al., 2009; Schlacher et al., 2014). For this reason, dunes may represent remnant habitat or refugia for wildlife in some areas that have otherwise been drastically modified, amplifying their importance for nature conservation (Bird et al., 2020; Delgado-Fernandez et al., 2019; Jackson et al., 2013).

Coastal dunes are dynamic ecosystems influenced by biophysical processes from the sea and land, which are both natural and anthropogenic in nature or intensity (Jackson et al., 2013; Lithgow et al., 2013; McLachlan, 1991). These processes shape vegetation and faunal assemblages within dunes and create phenomena such as zonation (Acosta et al., 2007; McLachlan, 1991). Zonation of vegetation shows an increasing gradient of structure, with increasing distance from a coastline, and is a consequence of strong directional environmental stresses interacting with dynamic geomorphologies, animal, and plant species, and creating transition zones between the sea and the hinterland (Bessa et al., 2013; Conti et al., 2017; Delgado-Fernandez et al., 2019; Prisco et al., 2021). Coastal dunes are naturally subjected to extensive seaward processes such as sand erosion and deposition, through substantial wind and wave action, which creates vegetation patchiness and topographical complexity (Jackson et al., 2013; Meager et al., 2012; Miyanishi and Johnson, 2021). These processes shape plant species distribution, and ultimately dune structure (Bird et al., 2020; Prisco et al., 2021).

There are two major processes which influence coastal dune (hereafter 'dune') form, and therefore influence the distribution of fauna within dunes. One of which can be classified as seaward processes. Natural marine processes create longshore heterogeneity associated with sand budgets (Defeo et al., 2009; Keijsers et al., 2016) and storms can radically and episodically reshape dunes (Jackson et al., 2013; Maslo et al., 2019; Stoddard et al., 2019) causing distributional shifts in flora and fauna (Maslo et al., 2019). Dune vegetation is a key determinant of dune form, and associated ecosystem composition and function (Mir-Gual et al., 2013) providing habitat for fauna (Ben-Ami and Ramp, 2013; Fischer et al., 2019, 2021; Swan et al., 2008). Vegetation richness is reduced near the beach, however landward of the dune peak, there is improved protection from seaward physical pressures (Nordstrom et al., 2009; Prisco et al., 2021) resulting in increasing vegetation structure and height away from the shore; such ecotones can be kilometres in width (Martin et al., 2018; Nordstrom et al., 2009). Some seaward processes influencing dunes are driven or enhanced by humans. Sea-level rise due to climate change creates a coastal narrowing effect ("squeeze") that is exacerbated by landward processes such as hinterland clearing (McLaughlin and Mineau, 1995; Pontee, 2013) or defence of human assets via coastal armouring or beach nourishment (Bessa et al., 2013; Defeo et al., 2009; Thom et al., 2018). Vegetation loss on the seaward margin due to erosion is common on coastal dunes, and worsened by sea level rise (Bessa et al., 2013; Nordstrom et al., 2009; Villaseñor et al., 2015). Another form of pressure from the seaward aspect of coastal dunes is the intensive and increasing demand of sandy shores as substrates for recreation and, in many countries, subsistence activities such as fishing (Defeo et al., 2009; Schlacher et al., 2011, 2014).

Coastal dunes can equally be influenced by landward processes. In natural states, coastal dunes often transition at the landward margin into intact terrestrial ecosystems, and so would exhibit ecological connectivity, including exposure to natural processes such as fire and grazing from wide-ranging herbivores (Allen and Mitchell, 2016; Roger et al., 2007; Swan et al., 2008). However, humans have radically altered ecosystems worldwide which abut the landward margins of coastal dunes (Defeo et al., 2009; Schlacher et al., 2014). Human settlement and agriculture are highly concentrated along coastal environments (Bessa et al., 2013; Malavasi et al., 2016; Schlacher et al., 2014) and are regarded as a key threat to coastal dune environments worldwide (Bird et al., 2020; Delgado-Fernandez et al., 2019). Coastal development essentially fragments formerly connected dune ecosystems into linear strips, conceptually equivalent to fragmentation of other terrestrial habitats (e.g., woodlands; Schlacher et al., 2014; Weston et al., 2009). Modified hinterlands often harbour invasive predators, grazers and non-native weeds which can spill-into or invade coastal dunes (Banks and Hughes, 2012; Stokes et al., 2009; Towns et al., 2006). These pests compete with and/or consume native flora and fauna potentially altering dune structure and faunal assemblages (Banks and Hughes, 2012; Fleming et al., 2021; Jackson et al., 2013; Stokes et al., 2009).

There is an urgent need to document and understand the role that natural and anthropogenic processes play in shaping coastal dune vertebrate fauna (Schlacher et al., 2014) to underpin improved land and coast-use planning and management (Van der Biest et al., 2020). This study investigates the factors which influence the occurrence of vertebrate fauna inhabiting the coastal dunes of Venus Bay, South Gippsland, Australia. Venus Bay is an ideal model coastal dune system with considerable hinterland variability ranging from urban, agricultural, and natural backings (Borchard et al., 2008; Borchard and Wright, 2010; Oates, 2019), and the dunes are exposed to seaward processes currently resulting in episodic coastal erosion (Oates, 2019). The vertebrate fauna of these dunes is poorly documented, as is the case for many other coastal systems. This study aims to:

1)
Document the vertebrate fauna which uses coastal dune systems in southern central Victoria,

2)
Examine the influences of hinterland land use practices on dune species occurrence; and,

3)
Identify the impact of seaward and landward processes on vertebrate faunal occurrence within dunes.

Section snippets

Study area

This study was conducted at Venus Bay, South Gippsland, Victoria, Australia (Fig. 1) from February to March 2021. Venus Bay belongs to a series of south westerly facing oceanic beaches in south-eastern Australia, west of the influence of the East Australian current, and exposed to the prevailing weather and swell (Thom et al., 2018). Venus Bay (35 km long) is backed by topographically diverse dunes and swales (Bird et al., 2020; Prisco et al., 2021). Hinterland land-use varies from urbanisation

Results

We recorded 69 084 images of vertebrate species from a total of 89 sites deployed for 20-30 days (median = 20). We identified 32 species (Table 2): 16 mammals, 13 birds, 2 reptiles and 1 amphibian. Rodents had the highest site occupancy, with House Mouse Mus musculus and Bush Rat Rattus fuscipes occupying 92% and 82% of sites, respectively. Sufficient data for single-species single-season occupancy modelling were available for ten species: House Mouse, Bush Rat, Swamp Wallaby ( Wallabia bicolor

Discussion

The coastal dunes of Venus Bay support a diverse species assemblage including: 16 mammals (seven native; nine introduced), 13 birds (12 native; one introduced), two reptiles (both native) and one amphibian (native). Greater diversity doubtlessly exists in the dunes described here, as one survey technique cannot detect all vertebrate fauna present (De Bondi et al., 2010; Rendall et al., 2021), and interannual and seasonal differences may occur (Hale et al., 2016). A variety of factors influenced

Conclusion

Dunes are complex habitats which harbour a variety of animals (Prisco et al., 2021; Rendall et al., 2019; Schlacher et al., 2014). Some processes shown to operate in terrestrial contexts (e.g., responses to habitat structure and hinterland modification) also operate in dunes, although the prominent effect of zonation may be a critical feature of coastal dune ecosystems. Overall, our findings support the conservation importance of coastal dunes due to the diversity of vertebrate fauna they

CRediT authorship contribution statement

Alicia Chadwick: Writing - original draft, Investigation, Formal analysis, Data curation, Conceptualization. Michael A. Weston: Writing - review & editing, Supervision, Resources, Project administration, Investigation, Conceptualization. Thomas Burns: Writing - review & editing, Resources, Investigation. Georgia Randall: Writing - review & editing, Investigation. Max Radvan: Writing - review & editing, Investigation. Anthony R. Rendall: Writing - review & editing, Visualization, Validation,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We acknowledge that this research was conducted on traditional lands, and we pay our respects to Elders, past, present, and emerging. Thanks to Michaela Mark for helping with data collection, to Calvin Lee for creating the NDVI layer for analysis satellite data was courtesy of the European Space Agency, and Phoebe Burns and John Peter for their expert assistance with species identification. Thanks also, to the Beach Ecology and Conservation Hub (BEACH) at Venus Bay for the support of this work.

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Natural and anthropogenic processes influence the occurrence of vertebrate fauna in coastal dunes

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Coastal dunes represent habitat for wildlife yet are chronically understudied and are threatened by anthropogenically driven processes from their land...

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The effects of shifting vegetation mosaics on habitat suitability for coastal dune fauna-a case study on sand lizards ( Lacerta agilis)

Abstract

Encroachment of tall grasses and shrubs in coastal dunes has resulted in loss of vegetation heterogeneity. This is expected to have negative effects on animal diversity. To counteract encroachment and develop structural heterogeneity grazing is a widely used management practice. Here, we aim to functionally interpret changes in vegetation composition and configuration following grazing management on habitat suitability for sand lizards. Aerial photographs taken over a period of 16 years were used to quantify changes in vegetation composition. A GIS-based method was developed to calculate habitat suitability for sand lizards in a spatially explicit manner, encompassing differences in vegetation structure and patch size. From 1987 to 2003 dune vegetation shifted from small patches of moss and sand to larger patches covered by shrubs and grasses. Grazing management did not have any significant effect on the overall level of heterogeneity, measured as habitat suitability for sand lizards. However, on a more local scale highly suitable patches in 1987 were deteriorating whereas unsuitable patches became more suitable in 2003. This inversion results from a broad shift with shrubs being a limiting habitat element in 1987 to sandy patches being the limiting element in 2003. Future changes are believed to negatively impact sand lizards. The habitat suitability model has proven to be a useful tool to functionally interpret changes in coastal dune vegetation heterogeneity from an animal's perspective. Further research should aim to include multiple species operating on different scale levels to fully capture the natural landscape dynamics.

Introduction

Dry coastal dune ecosystems are spatially structured, consisting of a fine scaled mosaic of patches which provide suitable habitat for many plant and animal species (De Bruyn 1997). This spatial heterogeneity arises from the interplay between aeolian dynamics, soil development and vegetation succession and the intensity of each of these processes is governed by elevation differences and spatial variation in dune slope exposure (Doing 1995; Ranwell 1972).

Dune ecosystems along the coast of North-western Europe are threatened by the expansion of tall, highly competitive grass and shrub species since the 1950s. This results in dense homogeneous vegetations with a thick litter layer (Ketner-Oostra and Sýkora 2004; Veer and Kooijman 1997). This process of grass and shrub encroachment is mainly caused by increased atmospheric nitrogen deposition (Jones et al. 2004; Kooijman et al. 1998), decreased intensity of grazing by rabbits after plagues of myxomatose and RVHD (Rabbit Viral Haemorrhagic Disease; Drees and Olff 2001; Ranwell 1963) and changes in land use practice (loss of marram harvest and agricultural use) (Provoost et al. 2009). The habitat degradation is manifested as a decrease and loss of open sand, early successional stages, small herbaceous plants and lichens, with concomitant loss of variation in microclimatic conditions (Maes and Bonte 2006; Stoutjesdijk and Barkman 1992).

Landscape heterogeneity is recognised to be an important driver for plant and animal diversity (Geerling et al. 2006; Huston 1979; Kerr et al. 2001; Verberk et al. 2006; Wiens 1989). Loss of heterogeneity threatens animal species that are characteristic for dunes by limiting their possibilities for thermoregulation, foraging and breeding (Bonte et al. 2004; Maes and Bonte 2006).

To counteract the effects of encroachment in coastal dune landscapes restoration measures are taken. Grazing is a widely used management practice in coastal dunes (Provoost et al. 2009), because it is relatively cheap and can be applied on a large scale and in undulating landscapes. A key priority aim of this type of management is the restoration and conservation of landscape heterogeneity (Hopkins and Radley 1998). Management by grazing can increase the spatial heterogeneity of the vegetation in some cases (Adler et al. 2001), but it remains unknown to what degree animals profit from such increases. In this study, we investigate how grazing by cattle and ponies in a Dutch dune area influences the vegetation and how these changes affect habitat heterogeneity from an animal's perspective. Basic properties of heterogeneity include habitat diversity (variation in patch identity) and habitat configuration (size and distances between patches) (Gusafson 1998; Verberk et al. 2006). Sand lizards Lacerta agilis are considered to be good representatives for coastal dune heterogeneity as they require a habitat with combinations of different patches for thermoregulation, foraging, hiding, hibernation and egg deposition (Edgar et al. 2010; Glandt 1991; House et al. 1980; House and Spellerberg 1983a). Sand lizards are especially interesting because they have been subject of intense debate, with many herpetologists voicing concern about the disturbing effects grazing can have when high stocking densities are applied (Edgar et al. 2010; Offer et al. 2003; Stumpel 2004). Finally, the sand lizard is a flagship species for nature management and conservation policy in coastal dunes and is listed in the EU Habitat Directive (Council directive 1992).

When investigating the relation between habitat heterogeneity and the abundance or diversity of its inhabitants, few studies analyse the influence of combinations of patch types in a spatially explicit approach, i.e. by using distance to other patch types or by using grain size of patches as variables in correlative analyses (Bonte et al. 2000; Dennis et al. 2002). As a measure of heterogeneity previous studies have used e.g., the availability or evenness of discrete structural elements (Tews et al. 2004), single vegetation variables (Pöyry et al. 2006; WallisDeVries and Raemakers 2001) or employed different classes of heterogeneity based on one or more vegetation variables (Gibson et al. 1992). In this study we focussed on the patch dynamics resulting from shifting vegetation mosaics in Dutch coastal dunes from a sand lizard's perspective. To this end we developed a spatially explicit GIS model to assess habitat suitability for the sand lizard. To functionally interpret changes in dry coastal dune heterogeneity for fauna, we (a) investigate changes in vegetation heterogeneity in grazed and ungrazed plots over a 16 year period, (b) determine the impact of these vegetation changes on habitat suitability for sand lizards, and (c) test whether this is reflected in the number of encountered sand lizards.

Materials and methods

Study site

The study area is located in the inner dunes near Castricum (Fig. 1), in the western part of the Netherlands (52º34′34 N; 4º38′41 E). In this area six plots were selected, three grazed and three ungrazed. The grazed area (56.7 ha) has an average grazing intensity of 0.17 Large Livestock Units (LLU)·ha −1·year −1. Open range grazing was introduced in 1999 and is done by ponies (year round) and cattle (June to March). It is known that ponies and cattle have a strong diet preference for graminoid species (Lamoot et al. 2005). The choice of plots, which was made on basis of visual effects of grazing in the field, coincides with this preference (Fig. 1). Effectively this diet preference also means that grazing intensity throughout the year likely exceeds the above mentioned grazing intensity. Both grazed and ungrazed plots were similar in size (0.5 ha) and geomorphology, and had no management differences up to 1999. All distinguished vegetation structure classes (Table 1) were present in the plots.

Map of the Netherlands showing its location within Europe ( left). Within the map of the Netherlands the location of the study area near Castricum is shown ( middle). On the right an aerial photograph of the study site in the inner dunes near Castricum is shown. The grazed area (56.7 ha) is indicated with a dashed line around it and grazed study plots are indicated with black stars and ungrazed plots with white stars

Table 1 Sand lizard habitat suitability score for coverage of structural vegetation classes within home ranges of sand lizard, classified as optimal configuration (3 points), suboptimal configuration (1 point), unsuitable configuration (0 points)

Vegetation cover maps

For the analyses, high resolution aerial photographs were used from three years (Table 2): before RVHD extinction of rabbits and massive expansion of grasses and shrubs (1987), after rabbit extinction and grass/shrub expansion, but before grazing management (1995) and after four years of grazing management (2003). Aerial photographs from different years were all taken in the beginning of summer, between the end of May and the beginning of July. Differences in vegetation cover due to seasonality are therefore not to be expected. The 1987 and 1995 photographs were scanned and geo-referenced to the already geo-referenced 2003 photos. Ten vegetation structures could be distinguished: sand, sand with algae, sand with mosses and grasses, mosses, grass, dense grass, tussocks, Salix repens, Hippophae rhamnoides and shrub/trees.

Table 2 Aerial photograph type, photographic scale and pixel size. The pixel size of the analogue aerial imagery is based on the digital scan taken from this image

ArcGIS, Erdas Imagine 8.x. and Definiens professional 5 were used to prepare images and to produce the vegetation cover maps (Definiens 2006; ESRI 2004; Leica-Geosystems 2004). Images were segmented into polygons using image texture such as differences in colour or shape and compactness or smoothness (Definiens 2006; Geerling et al. 2009). After segmentation the maps were classified and a stereoscope (type Wild) was used to verify the polygon outlines and interpret the vegetation structure. Fragstats 3.3 was used to calculate patch size and type (McGarigal and Marks 1995). Patches were divided into 11 size classes (<0.5 m ², 0.5 to 1.5 m ², 1.5 to 3.5 m ², 3.5 to 7.5 m ², 7.5 to 15.5 m ², 15.5 to 31.5 m ², 31.5 to 63.5 m ², 63.5 to 127.5 m ², 127.5 to 255.5 m ², 255.5 to 511.5 m ², >511 m ²).

Spatially explicit analysis of habitat suitability for sand lizards

To quantify habitat suitability for sand lizards and temporal changes therein, vegetation cover maps were related to the habitat use of the sand lizard. The initially identified ten vegetation structure classes were aggregated to five vegetation structure classes (Table 1), which have previously been shown to be important habitat elements for sand lizards (House and Spellerberg 1983a; b). The different structure classes were divided on basis of the height of the vegetation (Cooke 1991). Because there were no plants higher than one meter in the class of Salix repens & Hippophae rhamnoides at the studied plots, these shrubs were kept separate from the shrub/trees class which were all higher than one meter. Note that at different sites and different geographical regions the division between these classes can be different.

A GIS based method was developed to analyse the landscape from a sand lizard's perspective. The model, which uses a moving window analysis, calculated for each GIS raster cell (pixel) the relative coverage of each structure class within a circle with radius of 5.6 m. This translates to an area of 100 m ², fully covering a sand lizard's daily home range (Van Leeuwen and Van de Hoef 1976). Optimal and suboptimal habitat configurations reported by House and Spellerberg ( 1983a, b), Cooke ( 1991) and Glandt ( 1991) were used to score suitability for each structural class coverage (Table 1). Optimal and suboptimal coverage were awarded 3 points and 1 point respectively. Too low or too high coverage of any one structural class was deemed unsuitable and awarded no points. As five structure classes were used, habitat suitability score ranged from 0 (unsuitable) to 15 (optimal). The resulting maps show within-plot spatial variation in habitat suitability and allow evaluation of changes in overall plot scores as well as within-plot spatial shifts through time.

Number of encountered sand lizards

Sand lizard abundance was studied from April to September 2005. The six plots were censused 9 to 13 times under similar weather and daytime conditions. Visual encounter surveys were done by two people systematically scanning the total plot from one side to the other. The number of encounters and the time spent in a plot were recorded. It was also attempted to catch each encountered lizard. Caught lizards were photographed for individual recognition (Märtens and Grosse 1996) in order to estimate population size. Unfortunately not enough lizards were caught to give a reliable estimation for population size (data not shown). Therefore we only report the number of encountered lizards per man-hour per hectare. Although the time spent in each plot during one round was variable depending on the number of encountered lizards, total census effort was comparable between the grazed part (107 h) and ungrazed part (114 h).

Data analysis

To detect the major changes in both vegetation type and patch size, a Principal Component Analysis (PCA) was performed in Canoco for Windows version 4.0 (Ter Braak and Šmilauer 1998) on the ten vegetation classes subdivided in eleven size classes (110 species) for each plot in each year (total eighteen sites). Preliminary data analysis in Canoco indicated a short gradient length, making PCA the most appropriate ordination technique.

To test for effects of vegetation succession over the years (1987, 1995 and 2003) and management (grazing and no grazing) on habitat suitability for sand lizards, we performed a repeated measures analysis (Anova with Greenhouse-Geisser correction) on the average suitability scores. A t-test was used to test for differences in sand lizard numbers between grazed and ungrazed plots.

To illustrate how different vegetation structure classes contributed differently over the three years to the total habitat suitability score, we compared the two most disparate structure classes (" S. repens and H. rhamnoides" and "sand"). For this comparison we calculated the number of pixels making up each habitat suitability score (scores attributed to habitat suitability are derived from Table 1), and the number was then expressed as a percentage coverage (correcting for difference in pixel size between 1987 and 2003 and for differences in total area between plots). Differences in this percentage coverage were tested with Mann-Whitney tests for each habitat suitability score.

Results

Changes in vegetation heterogeneity

Patch size and ecotope type distribution differed between grazed and ungrazed plots in 1987, 1995 and 2003 (Figs. 2 and 3). Both grazed and ungrazed plots exhibited a change in configuration from small (1-4) sand and moss dominated patches in 1987 to larger (6-8) grass and shrub dominated patches in 2003 (Fig. 2). From 1987 to 2003 the grazed and ungrazed plots exhibited similar changes in class cover; shrub classes ( H. rhamnoides; S. repens and other shrubs and trees) and dense grasses increased, whereas moss and sand classes (sand; sand with algae and sand with mosses and grasses) decreased. For the ungrazed plots, most pronounced changes occurred after 1995, which coincide with an increase in woody classes ( Salix repens, Hippophae rhamnoides and shrub/trees) and patch size. In the grazed plots this shift had already occurred between 1987 and 1995 before grazing was introduced.

Principal component analysis of patch size and ecotope class distribution through time. The figure shows changes and their explaining factors from 1987 ( white) via 1995 ( grey) to 2003 ( black) from the three grazed ( rounds) and three ungrazed ( triangles) plots. Numbers (1 - 11) represent size classes going from 1 (<1 m2) to 11 (>511.5 m2) and are explained in the text

Average cover (%; mean; n  = 3) of the different ecotope classes through time for grazed and ungrazed plots

The average cover of the different vegetation structure classes was calculated (Fig. 3), plots of the same year and treatment were grouped because of high similarities (Fig. 2). In both treatments a 30-40% moss cover disappeared between 1987 and 2003, sand dominated patches decreased by approximately 60% and a 40% cover of grasses and woody species in 1987 increased to more than 90% in 2003. Small differences between treatments included a higher cover for the different classes of sand (sand; sand with algae and sand with mosses and grasses) and a lower moss cover in the ungrazed plots of 1987. In addition, stands of H. rhamnoides occurred only in the ungrazed plots.

Sand lizard habitat suitability

Whole plot average values for sand lizard habitat suitability scores did not differ between years and treatments (Table 3, Anova with Greenhouse-Geisser correction, p > 0.05). In contrast, on a smaller scale (within plots), large spatial shifts in habitat suitability occurred during the research period (Fig. 4). The occurrence of these large within-plot spatial changes without the co-occurrence of an overall change between year and treatment result from a spatial inversion of how suitable patches are distributed in the plot (Fig. 4): low quality patches became more suitable, whilst patches of intermediate and high quality became less suitable over time (Table 4). These shifts in habitat suitability correspond with an increase of S. repens and H. rhamnoides and a decrease in sand coverage (Fig. 5, Mann-Whitney, p  < 0.05).

Table 3 Mean values and standard errors (SE) of sand lizards habitat suitability score through time. There were no significant differences in lizard habitat suitability scores (Anova with Greenhouse-Geisser correction, p > 0.05) between years and treatment

A selection of plot cover maps ( left) accompanied by their habitat suitability maps ( right). Habitat suitability scores vary between 1 and 15, 1 representing unsuitable spots and 15 very suitable spots. Due to the window of 5.6 m radius (representing a lizard's home range) used in the habitat suitability analysis, the suitability maps are 5.6 m smaller on the side to prevent inclusion of no-data points

Table 4 Total habitat suitability class change from 1987 to 2003 (%; means; n = 6). Total suitability scores are divided into three classes: 11-15 (++), 6-10 (+) and 1-5 (−). To facilitate interpretation, grey area represent no change, black represent a negative change and white represent a positive change in suitability class. For instance, out of all the poor (−) habitat patches, which constituted about a third (34.7%) of the total area in 1987, some remained poor (37%), most improved (60%), while a tiny fraction (3%) became very good (++)

The number of pixels contributing to each habitat suitability score (scores attributed to habitat suitability are derived from Table 1), expressed as average% cover (means ± standard error; n = 6). The two most disparate structure classes are shown: S. repens and H. rhamnoides (woody vegetation, a) and sand (no vegetation, b). Years are shown separately 1987 ( grey), 1995 ( black) and 2003 ( white). Asterisks show significant differences across years for a given class (Mann-Whitney, p  < 0.05)

Number of encountered sand lizards

The average number of encountered sand lizards per man-hour per hectare in ungrazed and grazed plots were 4.5 (SE = 0.4) and 5.3 (SE = 0.5) respectively and did not differ between treatments ( T-test; p  > 0.05).

Discussion

Grazing and heterogeneity

Despite the implementation of grazing management in 1999, habitat development in terms of patch size and type from 1987 to 2003 was similar in all plots. The vegetation changed from being dominated by sand and moss in 1987, towards high cover of dense grass and shrub in 2003. Simultaneously, mean patch size increased (Figs. 2 and 3). Grazing did reduce the height of dense grass vegetation (pers. field obs.), but this was not detectable on aerial photographs. Although this may have slowed down expansion of tall grasses and shrubs, it appears insignificant compared to the autonomous vegetation succession in the area.

A variety of grazing effects is reported from other studies (Adler et al. 2001), leading to increases as well as decreases of spatial heterogeneity. De Bonte et al. ( 1999) report a decrease of dense grass in favour of sand, moss covered sand and low grass after five years of grazing with similar grazers and grazing pressure in a different dune area (Meijendel, the Netherlands). In another dune area (Zepeduinen, the Netherlands) a similar grazing intensity resulted in lower grass vegetation and increased structural heterogeneity, but similar to our results grass encroachment was not halted completely (Kooijman and Van der Meulen 1996). Grazer identity and intensity, soil properties and spatial scale of the study area can play a crucial role in explaining the different outcomes across the various studies in terms of the response in plant species composition and vegetation heterogeneity (Kohyani et al. 2008). This provides a cautionary note when comparing our results from a Dutch dune area to grazing effects in other dune areas inside and outside the Netherlands.

The failure of grazing management to counteract the expansion of grasses and shrubs in this study could be caused by the short period since grazing was introduced. Another important factor influencing the minor effect on tall grass cover might be the used grazing intensity. This intensity falls within the range of those used in other studies, it is however on the low to moderate end of the spectrum of applied stocking rates in similar habitats; e.g. between 0.15 and 0.46 LLU·ha −1·year −1 on Belgian dune grasslands (Kohyani et al. 2008), between 0.12 and 0.49 LLU·ha −1·year −1 on sand dune vegetation communities in the UK (FitzGibbon et al. 2005) and between 0.1 and 0.25 LLU·ha −1·year −1 on lowlands heathland in the UK (Symes and Day 2003). Other likely explanations are the combined effects of high levels of airborne nitrogen deposition and a very low natural grazing regime by rabbits, whose populations have decreased in numbers up to 90% between successive study years (1990-2003) in the whole of the Netherlands (Drees et al. 2009). Since changes in vegetation heterogeneity were most apparent when comparing plots over time, rather than comparing between grazed and ungrazed plots, we will focus the discussion on the effects of autonomous vegetation succession in relation to habitat suitability of sand lizards.

Sand lizard habitat quality

Sand lizards require a structurally complex habitat with combinations of different patches for thermoregulation, foraging, hiding, hibernation and egg deposition (Edgar et al. 2010; House and Spellerberg 1983a; b) and their numbers have been shown to decline when heterogeneity decreases (De Bruyn 1997; Jackson 1979). Despite pronounced within-plot spatial changes in heterogeneity (Fig. 4), average habitat suitability per plot neither changed in time, nor differed between grazed and ungrazed plots. In addition, field surveys in 2005 confirm the absence of differences in habitat suitability, showing no differences in sand lizard encounters between grazed and ungrazed plots. The absence of differences in sand lizard numbers when habitat suitability is comparable would also suggest there is not a strong, direct impact of the current grazing intensity (0.17 LLU ha −1 year −1) on sand lizards. This agrees with the findings of Edgar et al. ( 2010), who suggest that great negative effects on sand lizards were not to be expected because stocking rates were below 0.2 LLU ha −1 year −1, which is seen as a stocking rate from where negative effects are expected. The absence of differences in sand lizard numbers would seem to question the validity of the sand lizard as an indicator species for heterogeneity. However, in contrast to the stability of habitat suitability scores averaged over entire plots, pronounced changes of within-plot spatial differences in habitat suitability scores were observed. Sand lizards may thus be valid indicator species on smaller spatial scales. Spatial changes in habitat suitability partly resembled an inversion, with highly suitable locations deteriorating and unsuitable locations becoming more suitable through the years. This deviates from the more commonly observed pattern of habitat change, where the most suitable locations also remain suitable for the longest time, providing refugia in the face of habitat deterioration.

One could argue that the change of suitable location into unsuitable locations and vice versa is characteristic for dynamic dry coastal dunes and that despite shifting vegetation mosaics a status quo is preserved of suitable patches being present somewhere in the landscape. However, the relative contribution of the different structure classes to the sand lizard habitat suitability showed strong directional changes. In 1987 habitat suitability was constrained by the low cover of shrub ( Salix repens or Hippophae rhamnoides), while patches of open sand and low vegetation were too large. With a strong increase of shrubs together with a decrease in open sand and mosses, limitation of necessary structural elements hardly occurred in 2003, but instead habitat suitability was limited by low coverage of open sand. With ongoing succession and unchanged management, sand lizard habitat suitability is expected to decrease due to a further loss of open sand and pioneer vegetation, as well as an increase of coverage of tall grass, shrubs and trees. Three problems can be implicated. First, sand lizards require at least 1-1,5 m ² of open sand per hectare for oviposition (Strijbosch 1987) and maintaining 1-10% of bare soil, recommended for a good sand lizard habitat (JNCC 2009), can prevent these sites from becoming limiting. Second, loss of variation in vegetation structure reduces possibilities for thermoregulation, a problem documented for the closely related common lizard Zootoca vivipara (Herczeg et al. 2006). Third, a denser and more homogeneous vegetation may harbour lower prey densities, prey visibility and decrease foraging activity.

Practical implications

From the differences between whole-plot and within-plot habitat suitability for sand lizards, it is clear that the indicator function for heterogeneity of the sand lizard is scale-dependant. At the local (within-plot) scale level, the distribution of sand lizards could probably be a useful indication of within-plot habitat heterogeneity. Changes in within-plot habitat heterogeneity occurring over several years could thus be effectively traced through fine scaled sand lizard distribution monitoring. This is also recommended by Offer et al. ( 2003) who suggests that a good monitoring programme of reptiles and vegetation structure is essential as a precaution for negative effects in areas where grazing is recommended. At the regional (between-plot) scale level, habitat suitability has proven resistant to changes in habitat heterogeneity until present. It is expected to decrease with further vegetation succession and loss of open sandy patches. Changes in sand lizard population size at this scale most likely occur only after long ongoing and chronic habitat degradation, limiting its use as an early warning indicator. The abundance of an indicator species is ideally linked with natural landscape heterogeneity, with the species operating on a scale which is in accordance with natural landscape dynamics. As it will often be impossible to find a species fitting this profile, a multi-species approach is preferred with species responding to habitat heterogeneity at different scales (local to regional) (Maes and Van Dyck 2005; Verberk 2011).

The extensive grazing regime applied in our study area did not halt the expansion of grasses and shrubs and the loss of heterogeneity. Increase of grazing pressure can however have adverse effects on reptiles (Edgar et al. 2010) and other fauna of nutrient-poor grasslands, as also shown for snails (Boschi and Baur 2007). Management of dune areas should aim at reversing this encroachment and restoring habitat heterogeneity at multiple scales, ranging from local sandy patches, for a species as the blue-winged grasshopper Oedipoda caerulescens, to a mosaic of different vegetation patches for butterflies as the grayling Hipparchia semele (Maes and Bonte 2006) and insectivorous birds as the red-backed shrike Lanius collurio (Van Duinen et al. 2004). The key large scale management tool to achieve these goals is a sustainable reactivation of aeolian dynamics. Spatial differences in aeolian dynamics can create a fine scaled mosaic of patches with differences in soil development and vegetation succession beneficial for many plant and animal species (De Bruyn 1997; Doing 1995; Ranwell 1972). This is also essential for sand lizard conservation providing a suitable habitat with combinations of different patches for thermoregulation, foraging, hiding, hibernation and egg deposition (Edgar et al. 2010; Glandt 1991; House et al. 1980; House and Spellerberg 1983a). On a smaller scale, extensive grazing, emulation of grazing through mowing and emulation of aeolian dynamics through sod cutting are management practices which are in use nowadays. These practices, either separate or combined, may prove suitable for reversing encroachment and restoring heterogeneity of coastal dunes, but their planning will require a differentiation of measures in space and time (Edgar et al. 2010).

Conclusions

The use of a habitat suitability model has proven to be a useful tool to functionally interpret changes in dry coastal dune heterogeneity from an animal's perspective. Average habitat suitability proved unresponsive to changes in habitat heterogeneity until present but is expected to decrease with further vegetation succession and loss of open sandy patches. Monitoring the distribution of sand lizards as an early warning system will be more suitable for documenting habitat heterogeneity on a smaller scale. The grazing intensity used in this research did not halt expansion of grasses and woody species. Large scale reactivation of aeolian dynamics and small scale emulation of these processes are deemed most promising to offset the negative effects of encroachment. Habitat suitability models such as these can help site managers focus management efforts by identifying essential habitat elements. To fully capture the natural landscape dynamics we recommend expanding habitat suitability models to encompass multiple species operating on different scale levels and differing in their essential habitat elements.

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Acknowledgments

We thank the Provincial Water company North Holland for supporting and funding this study, especially Rienk Slings and Hubert Kivit for their assistance during the research. Henk Strijbosch and Ravon for their expert judgement and access to their literature database. Special thanks to Gemma Rutten for her assistance in collecting the lizard encounter data during field work. Finally, the paper improved by constructive comments of an anonymous referee.

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Wilco Verberk

Present address: Marine Biology and Ecology Research Centre, University of Plymouth, Davy Building, Drake Circus, PL4 8AA, Plymouth, UK

Authors and Affiliations

1. Bargerveen Foundation, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands

Bart Wouters, Marijn Nijssen, Hein Van Kleef, Eva Remke & Wilco Verberk

2. Centre for Sustainable Management of Resources, ISIS, Radboud University Nijmegen, toernooiveld 1, 6525 ED, Nijmegen, The Netherlands

Gertjan Geerling

3. Department of Environmental Science, Institute for Wetland and Water Research, Radboud University Nijmegen, toernooiveld 1, 6525 ED, Nijmegen, The Netherlands

Hein Van Kleef

4. Department of Animal Ecology and Ecophysiology, Institute for Wetland and Water Research, Radboud University Nijmegen, toernooiveld 1, 6525 ED, Nijmegen, The Netherlands

Bart Wouters, Marijn Nijssen, Eva Remke & Wilco Verberk

Corresponding author

Correspondence to Bart Wouters.

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Wouters, B., Nijssen, M., Geerling, G. et al. The effects of shifting vegetation mosaics on habitat suitability for coastal dune fauna-a case study on sand lizards ( Lacerta agilis). J Coast Conserv 16, 89-99 (2012). https://doi.org/10.1007/s11852-011-0177-9
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DOI: https://doi.org/10.1007/s11852-011-0177-9

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The effects of shifting vegetation mosaics on habitat suitability for coastal dune fauna-a case study on sand lizards (Lacerta agilis) - Journal of Coastal Conservation

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Encroachment of tall grasses and shrubs in coastal dunes has resulted in loss of vegetation heterogeneity. This is expected to have negative effects on animal diversity. To counteract encroachment and develop structural heterogeneity grazing is a widely used management practice.

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The dunes are home to many species which are perfectly adapted to live in the naturally shifting sand and the mosaic of habitat types that can be found in healthy dune systems.
From toads and lizards to butterflies and orchids, there are many different species that our work will help to protect. Some are rare while others are more common, but each of these species are specially adapted for life in a healthy sand dune environment. Meet some of our dune wildlife below, learn about the kinds of dune habitats they live in, and the conservation actions we're taking to protect them.

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The dunes are home to many species which are perfectly adapted to live in the naturally shifting sand and the mosaic of habitat types that can be found in healthy dune systems. From toads and lizards to butterflies and orchids, there are many different species that our work will help to protect.

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Rosebay Willowherb | The Wildlife Trusts

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A tall plant, Rosebay Willowherb is a successful coloniser; it can form dense stands of bright pink flower spikes on disturbed ground, such as woodland clearings, verges and waste ground.

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Eryngium variifolium | variable-leaved sea holly Herbaceous Perennial/RHS Gardening

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Find help & information on Eryngium variifolium variable-leaved sea holly Herbaceous Perennial from the RHS

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Global Biodiversity Information Facility. Free and Open Access to Biodiversity Data.

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Global Biodiversity Information Facility. Free and Open Access to Biodiversity Data.

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Sea Bindweed (Calystegia Soldanella) - Wildflower Web

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Find out all you need to know about Sea Bindweed (Calystegia Soldanella) on Wildflower Web. Learn about its habitat, distribution, and more.

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Learn about the identification, characteristics, and uses of the Kidney Vetch plant. Get expert advice on growing and caring for this wildflower at Wildflower Web.

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A scrambling plant, Common Vetch has pink flowers. It is a member of the pea family and can be seen on grassland, farmland and waste ground, as well as at the coast.

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Look for the small, pink, pea-shaped flowers of Common Restharrow on chalk and limestone grasslands, and in coastal areas, during summer.

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Russo et al. - 1988

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Shows a cross section of the grass leaf

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Species information

About

The dense, grey-green tufts of Marram Grass are a familiar feature of our coastal sand dunes, its spiky leaves featuring in many games during long summer picnics at the beach. But Marram Grass is not just a convenient child's sword or hiding place, it plays a vital role in stabilising the dunes, its fibrous, matted roots binding the sand down, which helps to encourage the colonisation of other plants. Well-adapted to a harsh life at the coast, its glossy, rolled-up leaves protect it from drying out.; it flowers in July and August.

How to identify

The dense tufts of spiky Marram Grass are a distinctive feature of this plant. Its leaves are rolled and it displays densely packed, golden flower spikes.

Distribution

Widespread around the UK's coast.

Did you know?

Marram Grass was once harvested and weaved into mats for barn roofs, nets for fishing and even shoes. Traditionally, each family had its own sand dune, but the whole village would often be involved in collecting the grass. Today, the importance of Marram Grass in stabilising these fragile habitats has curbed its harvesting.

How people can help

The Wildlife Trusts manage many coastal nature reserves for the benefit of the wildlife they support. You can help by supporting your local Trust and becoming a member; you'll find out about exciting wildlife news, events on your doorstep and volunteering opportunities, and will be helping local wildlife along the way.

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The dense, spiky tufts of Marram Grass are a familiar sight on our windswept coasts. In fact, its matted roots help to stabilise sand dunes, allowing them to grow up and become colonised by other species.

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If you've ever been to the sandy beaches of the UK's coastline, the chances are you will have seen marram grass! It is also known as European beachgrass. It is the tussocky, spiky, coarse type of grass that you definitely would not choose to sit on to enjoy your picnic! But it is these characteristics that have enabled craftspeople throughout centuries to fashion baskets and rope from its leaves and it has also been used for thatching roofs and making paper.

Marram thrives in shifting sand. It has long root systems and survives when the wind naturally blows lots of sand on top of it, simply growing up through the new deposits. Its root systems help to stabilise the sand enough to create embryo dune and semi-fixed dune habitats, which are vitally important habitats for many species of insect and plant which need sandy soils.

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Marram grass is tolerant of salty conditions, but it is also well adapted to wide daily temperature fluctuations and can even grow in places where the water table is far below ground.

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Martinez, Hesp & Gallego-Fernandez - 2013

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As mentioned in the previous chapter, humans have been responsible for changing the lithosphere and biosphere on Coastal Sand Dunes. The Stockton Bight Coastal Sand Dunes are no exception and humans have had both positive and negative impacts upon them.

1. Positive Impacts

a) Aboriginals, fire and the Encouragement of Biodiversity

The most positive human impact that has been made on the Stockton Bight Coastal Sand Dunes was by the Aboriginal people, particularly the Worimi Nation. The Worimipeople, through a practice called "fire stick farming", have actively encouraged vegetation growth.

As explained earlier, vegetation plays two important roles on Coastal Sand Dunes. Firstly, it helps stabilise dunes by trapping and stabilising the sand particles. Secondly, the secondary and tertiary vegetation zones often develop into thick forests, woodlands. wetlands and heaths which provide a habitat for many other flora and fauna species to thrive.

Some of the main vegetation species found at Stockton Bight -such as Banksias, Wattles, and Eucalypts- depend on fire for the propagation of their seeds and for the development of new growth.

By deliberately lighting fires, the indigenous peoples have contributed the growth of the thick forests and woodlands that were found in the secondary and tertiary vegetation zones. By providing an extensive habitat many other animal species have been able to thrive, thus making the local Aboriginal people partially responsible for the biodiversity along Stockton Bight.>

b)European Management

It has only been in very recent years that the Europeans have started to make positive impacts on the Coastal Sand Dunes at Stockton Bight. Unfortunately, the positive steps have been in response to the negative impacts that are outlined below. In recent years, European mangers have started to eradicate the introduced species such as Bitou Bush, reduce access to certain parts of the Dunes, restabilise the foredune , and conserve and protect threatened species etc. Many of these will be covered in more detail in the next chapter in contemporary management strategies.

2. Negative Impacts

Humans have adversely affected the Coastal Dunes at Stockton Bight particularly on the biophysical processes occurring in the accretion cycle, and on the flora and fauna in the biosphere.

These impacts have been caused by the following human activities:

Disruption of Sediment (sand) Flow

Coastal Development

Recreation use

Cattle Grazing

Introduction of weeds and pests

and Sand mining

The above human activities are a serious concern on the Stockton Bight, and are the main reasons why the Coastal Sand Dunes are considered an Ecosystem at Risk.>

In terms of the lithosphere, the accretion cycle has been adversely affected Dune vegetation has low elasticity (takes longer to recover). Most of the coast has already lost some of its intrinsic value, which may be costly and difficult to rehabilitate. Specific human impacts are examined below.

Disruption of Sediment Flow- Building of the Sea Wall

The accretion cycle is dependant on the flow of sediment along the coast. When humans alter the flows of sediment major changes take place in the coastal environment. If the flow of sediment is reduced or cut completely the consequences for dunes are immediate and direct as the outputs in the accretion cycle will outweigh the inputs.

At the southern end of the Stockton Bight , the building of the the large sea walls at the mouth of the Hunter River has had catastrophic effects on the sediment flow and depositing of sand along the beach around Stockton township. The sediment provided by longshore drift is not getting to the beach and dunes in that area. As a consequence the foredune area is receding back.

One major function that the foredune plays is to act as a storm buffer. The built environment in this area, especially the Stockton Caravan Park and Surf Club, are in danger of being claimed by the sea as each big storm brings with it destructive waves that erode the foredune area but the flow of sediment to replenish it has been altered by the sea wall. Costly rectification work is currently in place.

Coastal development

Coastal Dunes are located along an area that is desirable for human habitation as its intrinsic value has made it a popular place for where people want to live. Since demand for land and housing near coasts are high, coastal dunes have high economic worth (utility value). Thus, humans build large housing developments on Coastal Dunes.

In the Stockton Bight area intensive housing development has taken place. Firstly, the Stockton township was built on the hind dune area and has completely transformed it into an urban area.

In very recent years, developers are starting to build housing estates further north. Fern Bay is a recent housing development and by its own Species Impact Statement has found that there are a number of significant impacts that will take place on the biosphere.
...The site is also part of a local corridor of native vegetation and contains key habitats for threatened species in the region. Accordingly potential impacts on flora and fauna must be considered in this assessment...The site contains swamp forest, dry sclerophyll open forest and wet heath that supports habitat for a range of threatened species and ecological communities listed in the Threatened Species Conservation Act 1995 (TSC Act). The site forms part of a larger fragment of coastal woodland in the Fern Bay area and adjoins the floodplain of Fullerton Cove wetlands (a SEPP 14 wetland) and conserved within the Kooragang Nature Reserve. Thesite comprises three distinct vegetation communities including:-

Coastal sand apple Blackbutt forest

Swamp mahogany - paper bark forest

Wet heath - Tomago sand swamp woodland.

No threatened populations currently listed under the TSC Act and the Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act) have been recorded on the site. One Endangered Ecological Community (EEC), being the 'Swamp Sclerophyll Forest on coastal floodplains of the NSW north coast, Sydney basin and south east corner bioregions', is located in the swamp forest adjoining Nelson Bay Road. There are 41 threatened species listed under TSC Act that have the potential to occur within 10km radius of the site. A total of 37 threatened species and one endangered ecological community have the potential to be impacted by the proposal based on habitat requirements and previous studies on the site. Of these species, there were 12 species which have recently been recorded on the site which included:-

Newcastle Double tail orchid (Diuris praecox)

Wallum froglet (Crinia tinnula)

Hoary wattled bat (Chalinolobus nigrogriseus)

Eastern Freetail-bat (Mormopterus norfolkensis)

Greater broad-nosed bat (Scoteanax rueppellii)

Little bentwing-bat (Miniopterus australis);

Eastern bentwing-bat (Miniopterus schreibersii oceanensis)

Yellow-bellied sheattail-bat (Saccolaimus flaviventris)

Grey-headed flying-fox (Pteropus poliocephalus)

Powerful owl (Ninox strenua)

Masked owl (Tyto novaehollandiae)

Squirrel glider (Petaurus norfolcensis)

The development proposes to clear 70.2 hectares of vegetation, which includes 495 habitat trees. This clearing comprises 9.7ha of swamp forest, 15ha of wet heath and 45.5ha of dry open forest from the site. The following potential impacts of the proposal were identified by the applicant in the Species Impact Statement (SIS):- Of these potential impacts, the greatest impacts include habitat loss, habitat fragmentation and the potential impact on the local and regional corridor.
Source: Extract from NSW Department of Planning (2006)MASTER PLAN ASSESSMENT: Fern Bay Estate No 85 Nelson Bay Road Fern Bay Port Stephens Local Government Area pp.38-39

Recreational Uses

People visiting beaches have a major impact on dune ecosystems. What Research demonstrates that coastal areas that have high rates of visitor pressure will be subject to significant degradation. One of the most common reasons for this is the overall loss of plant life.

As people try to make their way to the beach they trample plants. As `holes' appear in the dune vegetation, introduced weeds are given a chance to grow. These tend to be more resilient and can better cope with trampling. The foredune vegetation, in particular the grasses, are the most easily damaged. These are also some of the most important species because they protect the least stable part of the dune system.

The tyres of four-wheel drive vehicles and the hooves of horses and camels also destroy dune vegetation and their weight leads to greater soil compaction. Compact soil has less oxygen, which reduces plant growth and makes it even more difficult for plants to recover. On some beaches where vehicles have been banned, the effects of their use can still be seen up to 10 years later.

Dune systems have also been flattened to provide land for sporting facilities, parking areas and parkland.

Sand mining and Extraction

Sand mining is one of the most disruptive and controversial of land uses carried out in the coastal environment because it involves the total removal of dune vegetation. When mining takes place in dune systems supporting climax (a well balanced) plant communities, the process of rehabilitation can take decades and may never achieve the ecological diversity of the dunes before the mining as the elasticity of dune vegetation is low.

Dunes are mined for silica, and minerals that help in the production of titanium. Furthermore, Sand is actually removed for construction and replenishment in other beaches (Beaches in Hawaii have Stockton Sand on them).

The method of Sand mining is also very destructive to the lithosphere and vegetation communities. Sand mining is normally carried out by dredging sand and separating heavy minerals from the silica on board a floating concentrator plant in a dredge pond. The dredge and other equipment move along a predetermined path about 100 m wide. The path is cleared of vegetation about a month prior to mining, the vegetation burnt and the topsoil stockpiled. The path is cleared 100 m in front of the dredge pond.

After an area is mined, rehabilitation begins along the dredge path. Tailings (leftovers) are reshaped and stabilised to resemble existing landforms, and are revegetated to resemble existing plant communities.

Sand extraction for commercial purposes is also very disruptive. Sand is used in a range of industrial and construction processes. The impact tends to be greatest in dune systems adjacent to large urban centres.

At Stockton Bight both these types of sand mining operations are occurring.

Image shows the site of Boral's Sand Mining Operation. The area clear of vegeation in the center is the old dredge pit from silica mining.

Introduced Species and Weeds: Rabbits and Bitou Bush

Coastal dunes are fragile ecosystems. To survive in such harsh conditions, plants must be able to tolerate poor soils, strong winds and salt spray. Given such conditions, it is not surprising that dune ecosystems are dominated by highly specialised plant species. However, like most highly specialised species, dune vegetation is vulnerable to changes in its environment, including invasion by weeds.

Most infestations are the product of human activities in the coastal zone. In some cases, plant species, which later become weeds, have been introduced deliberately to stabilise dunes. Bitou Bush is an example of this (click this hyperlink to find out more about bitou bush) In other instances, weeds are introduced via the wheels of off road vehicles, the soles of shoes and the faeces of cattle and birds. Eradicating weeds is often very labour intensive (and therefore expensive) and exposes the disturbed areas to wind erosion.

Rabbits are one of the most destructive species ever introduced to Australia. They have spread out across the continent, causing significant damage in many different environments. In the coastal dunes they eat the grasses and other vegetation, reducing the ground cover and exposing sand to wind erosion. The burrows also destabilise the dune structure.

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As mentioned in the previous chapter, humans have been responsible for changing the lithosphere and biosphere on Coastal Sand Dunes. The Stockton Bight Coastal Sand Dunes are no exception and humans have had both positive and negative impacts upon them.

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Coastal sand dunes are habitats created by sand, seashell fragments and other sediments that are moved by wave and wind action along a coastline or beach until they become trapped above the strandline. This usually occurs where vegetation is growing as their roots and leaves help to bind the sand together, preventing the sand from being blown away by the wind. There are several different types of sand dunes, categorised by their position on the shoreline, age, morphology and stability:

Embryo dunes: The youngest dunes at their earliest stage of development, usually closest to the shore and may still be covered by high tides. This area usually has high salinity and is a very dry environment with rapid drainage and a lot of exposure.

Mobile dunes: These are dunes that are no longer covered by the highest tide but are still affected by wind; sand gets blown from the beach onto, over and away from these areas.

Semi-fixed dunes: This is where vegetation cover has become more continuous with fewer areas of bare sand.

Fixed dunes: These are dunes that have very limited free space, with few areas of bare sand and almost continuous vegetation.

Dune slack: The low-lying depressions between sand dunes. These areas can often become filled with fresh or brackish water, creating small wetlands known as interdunal wetlands or interdunal ponds. These areas can warm quickly as they're often very shallow, providing an ideal habitat for many invertebrates.

Dune scrub: A later successional stage, where a stable dune has been colonised with scrub species. These areas can continue to develop into dune-heath and older woodland.

Sand dunes can be rich in wildlife and are important habitats for birds, reptiles, invertebrates, a variety of plant species, lichens and fungi. This is particularly the case in older, more stable dune habitats. They are classified as UK BAP Priority Habitat and several Priority List species have been recorded utilising sand dunes.

What species can you find here?

Flora

Differences in flora diversity can be found depending on the position, age, morphology and stability of the dunes. Sand dunes that are still inundated at high tide can be dominated by halophilic (salt-tolerant) plants, whereas dune slack areas may be filled with fresh groundwater, allowing them to support several freshwater plant species. Areas of low stability will most likely see lower plant diversity, with the community present dominated by pioneer species. More stable dunes are generally dominated by woody plants and have higher diversity.

Sea sandwort (Honckenya peploides)

This is one of several pioneer species usually found in embryo dunes, as it is highly stress-tolerant. These plants allow sand to begin to accumulate, raising the top of the dune above the high tide level, while also adding organic matter to the sand through dying and decaying. This allows the sand dune to better retain water, allowing other plants to colonise the area.

Marram grass (Ammophila arenaria)

This is a dune building grass as it is tall and robust, with matted roots, therefore it is very effective at trapping and stabilising sand. It can help to form very high mobile dunes as it grows at a rate of 1m per year. It is usually the dominant plant on mobile dunes and is a familiar sight on many of our coasts. By stabilising the sand and adding nutrients through its dead leaves, this plant can allow sand dunes to be colonised by many other plant species.

Harebell (Campanula rotundifolia)

As sand dunes become more fixed and vegetation cover becomes more continuous, the area can be very species-rich. Many wildflowers, including harebells, can be found there, providing a food source for species such as invertebrates. Due to the wide range of environmental factors in these habitats, such as wind, salinity levels and availability of shelter and fresh water, there is often a huge variety of wildflowers.

Harebells, also called bluebells of Scotland, are tough and resilient plants, living in dry, open areas such as sand dunes. While their flowering period can vary, it's usually from July to November in the British Isles, providing a vital source of nectar for bees during the autumn.

For more examples of wildflowers, check out our guide to UK wild flower identification.

Silver birch (Betula pendula)

The final successional stages of sand dunes include colonisation by woody plants, creating dune scrubs and, finally, deciduous woodland. These woodland are often lower in species diversity, as woody species out-compete others, but the habitat will remain stable for extended periods, barring any disturbance. The type of vegetation present in the climax stage is determined by a number of factors, such as climate, exposure, soil pH, grazing level and management type. Birch trees are one of the woody species that can colonise sand dunes, particularly acidic dunes with open areas for young birch trees to grow.

Fungi

While fungi are usually associated with damper habitats, there is a variety that can be found in sand dune habitats, such as the earthtongue fungus (Glutinoglossum glutinosum), dune stinkhorn (Phallus hadriani) and several puffball species. There are also rare species that can only be found in sand dunes.

Dune waxcap (Hygrocybe conicoides)

This species of waxcap occurs mainly on short grass in coastal sand dune habitats, such as on the edges of dune slacks. Waxcaps, fungi in the genus of agarics, or gilled fungi, are usually brightly coloured fungi with dry to waxy caps. They are mainly associated with unimproved grasslands, though outside of Europe they are more commonly found in woodland. Dune waxcaps resemble the blackening waxcap ( Hygrocybe conica) when young, but older dune waxcaps only darken slightly, usually just on their stem, unlike the blackening waxcap.

Collared Earthstar (Geastrum triplex)

While collared earthstars are most likely found in woodlands, particularly those with a high level of leaf litter, they can also be found on sand dunes. This star-shaped fungus initially looks like a ball, similar to a puffball, before splitting open. Other earthstars, including the dwarf earthstar ( Geastrum schmidelii), can also be found in sand dune habitats, particularly mature sand dune systems. They're often found in colonies with several fruitbodies growing together.

Fauna

Sand dunes support a diverse range of fauna species, many of which are specifically adapted to live in these dynamic habitats. Similarly to shingle beaches, which will be covered in another article, this area is a key habitat for several ground-nesting birds, such as the Ringed Plover and Skylarks, grazing species such as rabbits, and invertebrates such as bees, digger wasps and other insects.

The red-banded sand wasp (Ammophila sabulosa)

Sand wasps reproduce by hunting caterpillars, paralysing them using their sting and burying them in burrows with the sand wasp's egg. The females dig their burrows in sandy ground, with a nearby area of vegetation that would support their prey. Areas of sand dunes can be rich in invertebrate species, particularly where diverse vegetation is present.

Northern Dune Tiger Beetle (Cicindela hybrida)

This rare beetle hunts on bare sand, preying on ants, spiders, moth larvae and flies. As they need areas of open, moving sand, they are less likely to be found in older, more stabilised sand dunes. Therefore, lack of management allowing succession and reduced sediment deposition due to development or flood defences reduce the availability of suitable habitats. Conservation efforts to restore mobile sands and remove areas of scrub are helping to provide more habitats for the northern dune tiger beetle.

Sand lizard (Lacerta agilis)

Sand dunes support a variety of vertebrate species, including the sand lizard, one of the UK's rarest reptiles. Their distribution is restricted to a small number of sites, such as protected heathlands and sand dunes. They require sunny habitats with vegetation for shelter and undisturbed, open sand to lay their eggs. Their numbers are impacted by habitat loss but there are several conservation efforts working towards increasing their populations. These involve a combination of habitat restoration, monitoring, reintroduction and encouraging beneficial policies and practices.

Sparrowhawk (Accipiter nisus)

Several birds of prey use sand dune habitats as hunting grounds due to the presence of ground-nesting birds, lizards and some grazing species such as rabbits. Sparrowhawks can be found across Britain and Ireland, mainly in gardens, woodland and urban settings, but they can also be found on sand dunes, particularly if woodland is close by. They prey mainly on small birds, but they have also been recorded taking bats.

Chough (Pyrrhocorax pyrrhocorax)

Once extinct in Britain, Choughs now have a growing population on the Cornish and Welsh coasts, as well as a few other spots around the UK. They hunt invertebrates and larvae in the exposed sandy soils of sand dunes, using their long, curved bills. With only a small population in the UK, it is important to maintain suitable areas of habitats, therefore a number of projects are reintroducing grazing species to dunes. These species help to maintain areas of open ground and short grass, preventing sand dunes from becoming scrubland.

For more information on other species that may occur in sand dune habitats, including reptiles, coastal birds, waders and other mammal and bird species, check out some of our other guides to UK species identification.

Threats

The main threats to coastal sand dunes are development, recreational use, flood defences, falling water tables, climate change, invasive species and poor management. The development of housing, industry and areas such as golf courses can result in the damage or destruction of sand dune habitats. This, along with recreational use, such as excessive pedestrian and vehicular use, can increase levels of erosion and modify vegetation. Fragile sand dune habitats can be altered, reducing their stability and their ability to support diverse wildlife.

Poor management allows encroachment by shrubs and trees that, if left unchecked, could turn sand dune habitats into woodland areas, which can impact their suitability for specialist species. Flood defences can impact the natural processes of sediment removal and deposition, which can prevent sand dunes from developing or growing. These areas can become depleted if there is not enough sediment deposited to replace the amount removed by wind or wave action. The creation of harbours and other coastal structures can also disrupt natural sediment processes. Alternatively, these structures can also prevent sediment removal, causing a build-up of sediment.

Further threats include invasive species, such as cordgrass ( Spartina anglica), which can dominate sand dunes, reducing the abundance and diversity of native plant species and reducing the number of animals that the area can support. Climate change can also threaten this habitat, as increasing intensity and frequency of storms can impact how sand dunes are formed. Sea-level rise, in combination with development, can also reduce the amount of area available for this habitat to form; this is termed coastal squeeze.

While grazing is used as a method for controlling over-stabilisation and succession, overgrazing can also impact sand dunes. It can reduce the development and spread of vegetation, preventing sand stabilisation and, therefore, reducing the diversity and abundance of the species the habitat can support. This also allows sand dunes to become depleted by wave or wind action, particularly where structures such as flood defences and development have reduced sediment deposition.

Conservation

To manage the impacts of these threats, many sand dune areas have been given Site of Special Scientific Interest (SSSI) designations, which control the amount of development that can occur. Soft engineering approaches to flood defences including beach replenishment, the restoration of stabilised sand dunes and managed realignment, where areas are allowed to be inundated by the sea, can often be a more natural approach to reducing the impacts of waves compared to hard engineerings, such as sea walls and breakwaters. These can allow the natural process of sediment removal and deposition, facilitating the development of new sand dune environments.

As mentioned, sand dunes are subject to natural habitat succession, often ending in a stable deciduous woodland habitat. To maintain sand dune habitats, encroachment by woody species must be controlled and areas of open, mobile sand should be created as this prevents soil development and, therefore, over-stabilisation.

Areas of significance

Lindisfarne National Nature Reserve, Northumberland

Braunton Burrows, North Devon

Holkham NNR, North Norfolk

Kenfig NNR, Glamorgan, South Wales

Forvie NNR, Aberdeenshire, Scotland

Further reading
The Biology of Coastal Sand Dunes Sand Dune Conservation, Management and Restoration Field Guide to Coastal Wildflowers of Britain, Ireland and Northwest Europe Wildflowers of the Sefton Coast Beaches and Coasts Beach and Dune Restoration
Coastal zones are becoming increasingly topical as they face relentless pressure from a number of threats. This book provides a comprehensive introduction to the formation, dynamics, maintenance and perpetuation of coastal sand dune systems.
Sea of Sand: A History of Great Sand Dunes National Park and Preserve
This book deals with the development of temperate coastal sand dunes and the way these have been influenced by human activity. Options for management are considered and the likely consequences of taking a particular course of action highlighted.

This field guide covers more than 600 species of wildflowers and other coastal flora found in Britain and Ireland, and coastal mainland north-west Europe. Detailed species accounts describe the wildflowers, grasses, sedges and rushes that occur on the coast or in abundance within sight of the sea.

This book describes the typical wildflowers associated with each of the Sefton Coast's main habitats from the saltmarshes and 'green beaches' to the sand-dunes; the latter showing a sequence of successional stages running inland, from the newly-formed strandline and embryo dunes, through mobile and fixed-dunes to older woodland and dune-heath.

A new edition of a unique textbook that provides an exhaustive treatment of the world's different coasts, with a focus on climate change sea-level rise. Seeking to better educate students and readers about the sustainability of coasts and coastal environment, this exciting book offers enlightening coverage of coastal geology, processes and environments.

This new edition continues the theme of the first edition: the need to restore the biodiversity, ecosystem health, and ecosystem services provided by coastal landforms and habitats, especially in the light of climate change. This will be valuable for coastal scientists, engineers, planners, and managers, as well as shorefront residents

The Great Sand Dunes sprawl along the eastern fringes of the vast San Luis Valley of south-central Colorado. Sea of Sands is the definitive history of the natural, cultural, and political forces that helped shape this incomparable landscape.

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The NHBS Introduction to Habitats: Sand Dunes

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Coastal sand dunes are habitats created by sand, seashell fragments and other sediments that are moved by wave and wind action along a coastline or beach until they become trapped above the strandline.

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Our beaches and dunes are so popular that we put them under tremendous pressure. Where beaches can take a lot of coming and going, dunes are much more fragile. The tough plants that bind dunes in place are actually not suited to being walked on and die back very quickly with human trampling. The sand is then free to be blown away.

The vegetation on dunes is an essential feature in maintaining stability of the dune system. Damage to this vegetation caused by beach users treading a common path is sufficient to cause extensive instability over a large area due to the creation of vulnerable erosion routes.

Recreational activities such as pedestrian traffic, cars, caravan parks, horse riding and scrambling can seriously damage dune vegetation and increase the rate of sand loss through wind erosion. This loss of sand reduces the overall mass of the beach and sand dune system which acts as a buffer to the sea.

Pedestrian traffic resulting in the trampling of vegetation is the most widespread form of damage to dune systems caused by human activities. Probably the most seriously affected areas on the Irish coast are sand dunes that are subjected to unmanaged access can experience severe vegetation damage followed by soil and sediment erosion.

Through the development of networks of paths and tracks accessing the beach is where most of the damage generally occurs. It is usually on the access routes to the beach through the development of a network of paths and tracks that most of the damage occurs.

These networks of informal paths become centre for erosion and are rapidly enlarged by the wind, eventually forming gullies and blow outs. Paths across the top of dunes are most at risk where wind speeds are higher and path slopes often steeper.

In some areas the cumulative pressures of vehicles, pedestrians, camping and sporting activities have caused serious deterioration of vegetation and increased the risk to the stability of dune systems.

Dune Blowouts

Blowouts are sandy bowl like depressions in a sand dune caused by the removal of sediments by wind. They tend to form when the wind erodes into patches of bear sand where there has been a reduction or damage to vegetation. At exposed sites even a few people occasionally walking across a foredune may disturb the vegetation sufficiently to initiate blowouts.

Blowouts typically advance through various stages of development from erosional notches and hollows, to early blowouts, to large blowouts and then potentially to re-vegetating and stabilised blowouts. Where necessary, vegetation cover should be maintained either by keeping people out of the dunes or by appropriate infilling and replanting options.

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Supporting a Low Carbon and Climate Resilient Ireland

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Impact of Human Activities on Coastal Vegetation

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Impact of Human Activities on Coastal Vegetation

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Calvao, Pessoa & Lidon - 2013

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Dynamics, threats and management of dunes - MarineSpecies Introduced Traits Wiki

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From MarineSpecies Introduced Traits Wiki

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Dynamic Dunes

Dunes are naturally dynamic. However, over recent decades, dunes across north-west Europe have become over-stabilised, due to a combination of reasons. We have been studying change over time at Newborough Warren using a chronosequence (studying dunes of different ages). This suggests that changes in climate and increases in nitrogen deposition are important factors in promoting dune stability and soil development, as well as reductions in traditional management practices such as grazing. Interestingly, many of these changes started before the rabbit population was devastated by myxomatosis.

[Link to Jones, et al (2008). Factors controlling soil development in sand dunes: evidence from a coastal dune soil cronosequence. Plant and Soil, 307 (1-2). 219-234.]

[Link to Jones, et al (2010). Factors affecting vegetation establishment and development in a sand dune chronosequence at Newborough Warren, North Wales. Journal of Coastal Conservation, 14 (2), 127-137.]

Dune slack wetlands are sensitive to climate and nutrient enrichment

Hydrological change

Dune slack plant and animal species depend on the groundwater regime, but their requirements are poorly understood. We characterised hydrological tolerances of dune slack vegetation across four UK sites. A 20 cm difference in average water table regime separates wetter and drier slack communities, and only a 60 cm difference separates the wettest slack community from dry dune grassland. However, while we know that water tables can vary substantially from one year to the next, we are still not sure how quickly plants respond to changes in hydrology.

[Link to Curreli, et al (2013). Eco-hydrological requirements of dune slack vegetation and the implications of climate change. Science of the Total Environment, 443, 910-919.]

Groundwater nutrients affect dune slacks

We set up a study to assess the impacts of nutrients in groundwater on dune slack plant communities. This showed changes in species composition at very low nutrient concentrations: as little as 0.2 mg L⁻¹ dissolved inorganic nitrogen in groundwater (equivalent to 0.9 mg NO ₃ L⁻¹).

[Link to Rhymes, et al (2014). Evidence for sensitivity of dune wetlands to groundwater nutrients. Science of the Total Environment, 490, 106-113.]

Field evidence of impact

We re-surveyed dune wetlands in England after a 22 year interval, in a study for Natural England. Results show a 30% loss in wetland extent, a change from wetter to drier vegetation types at many sites, and a consistent increase in nutrient status of the plants. This suggests rapid change in an important habitat for lowland biodiversity.

[Link to Stratford, et al (2014). Survey and analysis of vegetation and hydrological change in English dune slack habitats. Final report to Natural England.]

Nitrogen impacts on dunes

Survey Evidence

Nitrogen is one factor contributing to over-stabilisation of dunes. Because it stimulates plant growth, fast growing species outshade smaller and slower-growing species, leading to a loss in diversity. A gradient study suggests that higher levels of nitrogen pollution from the atmosphere have resulted in a 50% loss in species across much of the UK, compared to the cleanest sites.

[Link to Field, et al (2014). The role of nitrogen deposition in widespread plant community change across semi-natural habitats. Ecosystems, 17 (5), 864-877.]

Experimental Evidence

Earlier work showed that nitrogen also alters soil processes in dunes, with more nitrogen available to plants. We set up an experiment in 2003 to see whether management by grazing would reduce the effects of nitrogen. Results showed that nitrogen is taken up and stored in the vegetation, but has not yet had an effect on plant composition. This may because plant growth is limited by other nutrients.

[Link to Jones, et al (2004). Changes in vegetation and soil characteristics in coastal sand dunes along a gradient of atmospheric nitrogen deposition. Plant Biology, 6 (5), 598-605.]

[Link to Plassmann, et al (2009). The effects of low levels of nitrogen deposition and grazing on dune grassland. Science of the Total Environment, 407 (4), 1391-1404.]

[Link to Ford, et al (2016). Nitrogen and phosphorus co-limitation and grazing moderate nitrogen impacts on plant growth and nutrient cycling in sand dune grassland. Science of the Total Environment, 542 (A), 203-209.]
Photo: Applying nitrogen treatments in a Nitrogen x Grazing experiment
Developing indicators of nitrogen impact

Recent work for the JNCC and for the Scottish Environment Protection Agency (SEPA) is designing ways to assess whether a particular site is impacted by nitrogen deposition. This will use plant abundance data collected on-site, and calculating different indicators such as average vegetation height, grassiness of the vegetation, plant species richness and presence of nitrogen-loving (nitrophiles) and nitrogen-hating (nitrophobes) species. Combining information from these indicators and comparing with data from other sites is a powerful way to detect whether a site is being affected by nitrogen.

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Dunes are naturally dynamic. However, over recent decades, dunes across north-west Europe have become over-stabilised, due to a combination of reasons. We have been studying change over time at Newborough Warren using a chronosequence (studying dunes of different ages).

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The atmosphere is a very important biophysical component in Coastal Dune Ecosystems.

Wind, temperature,and precipitation are key climatic and weather factors that play a significant role in the moving of sand particles in the accretion cycle on Coastal Sand Dunes and in providing the conditions for the vegetation to grow.

Wind

The single most important factor in determining the shape and extent of Coastal Sand Dunes is wind.Wind helps shape, dry , move, and weather sand.

Coastal Sand Dunes are most likely to develop in coastal regions that experience strong onshore prevailing winds (wind that blows on to the shore from the sea. For this reason the most extensive dune ecosystems are found in the world's temperate (hot summers cold winters) and arid (dry) tropical climatic zones.

In the Stockton Bight, where the Dune System is located, the prevailing winds changes from season to season but 75% of the wind is onshore blowing in from the south-east most of the year round.

AEOLIAN TRANSPORT

The word AEOLIAN is a fancy way of saying wind!

Wind is a major contributor to the erosion of Sand particles on dunes but also it plays a role in the movement of sand on dunesin the accretion cycle.

Sand is moved through three Aeolian Transport processes: Saltation, Creep, Suspension. Figure 1.2.5 below illustrate these processes. If the grain is any larger than around 1 cm in diameter it will be too big for any form of Aeolian transportation.

Saltation

Have you ever noticed while lying on the beach that tiny sand particles seem to be bouncing around like jumping beans? Well, this is one of the most common ways that sand is moved on Sand Dunes. This bouncing motion is called SALTATION.

Sand particles are moved in a current of wind by a series of bouncing movements.

As the wind strikes the ground it causes turbulence, meaning the air moves in several directions. This causes the sand grains to become loosened and easily moved.

If the wind has enough velocity (speed) it will cause the sand grains to begin moving. The amount of speed necessary to move the sand particles will change depending on how big the particle is, how much vegetation is present and how wet the sand is.

As the sand grains begin to move along the ground they strike other grains. This collision can cause one or more of them to bounce into the air.

Once in the air, the grain is moved by the stronger winds that exist higher above the ground surface.

Gravity soon causes the grain to fall back to the ground. The grains generally strike the surface at an angle ranging from 10 to 16 degrees. This angle is perfect for continued motion, if the grain falls on a rocky or other hard surface it will simply bounce into the air again. Should the grain fall back onto a sandy surface, the falling grain is likely to knock another grain, causing it to bounce and setting off a chain reaction. This reaction eventually sets in motion the entire sand surface.

Surface Creep

Grains of sand that are too large to be moved by saltation are transported by surface creep.

Surface creep occurs when the larger grains of sand are dislodged by the impact of falling grains.

The grains roll along the surface of the ground, being pushed by the smaller falling grains.

About one fifth of sand movement is caused by surface creep.

Suspension

Very tiny particles of sand are most commonly moved by suspension.

In this process the particles are carried by the wind, often well above the ground. They are too small to be influenced by gravity and they may travel for thousands of kilometres before they finally return to earth, often as the nuclei of a raindrop.

This type of transport is most commonly seen in vast dust storms that occur in arid regions, but it does account for a small proportion of sand moved along coastlines.

Temperature

Temperature affects the drying of the sand and the ability for vegetation to be present

Temperature affects how fast sand dries as wet sand cannot be moved by Aeolian transport.

Furthermore, temperatures together with rainfall influence the type of dune vegetation present. The more vegetation present the more easily sand can be stored as the roots of many vegeation hold the sand dunes together.

In the Stockton Bight area, temperatures are mostly moderate with the average daily maximum in summer ranging from 21 to 27°C and in winter it is 10 to 15°C.

There are no frosts because it is on the coastline. Thus, the temperature assists in the accretion cycle by providing enough heat to dry the sand to be able to be transported by wind and it assists by creating the right temperatures for enough vegetation growth to be able to trap and store the sand that creates the high dune systems and the reservoirs needed to replenish after removal.

Precipitation

The amount of Precipitation determines how wet the sand gets and assists in the ability of vegetation to grow.

Precipitation influences the vegetation cover, which helps stabilise the sand on Coastal Sand Dunes. Thus, it plays a role in the storage of sand in the accretion cycle.

Furthermore, heavy rainfall can erode steep dune faces but the wet sand is less prone to erosion by wind. Thus, playing a role in the removal of sand in the accretion cycle.

In the Stockton Bight area,the proximity to the sea allows for precipitation to be spread evenly through the year.

The wettest months are January to June, especially March. The most intense falls occur in summer storms. The average rainfall in the Hunter Region is 737 mm and 1328 mm at Port Stephens. Precipitation at the Bight varies from 1000 mm near the Hunter River to 1300 mm in the east.

Enough precipitation is present in the Stockton Bight area to assist in the formation of dune vegetation.

Furthermore, precipitation it is not constant and heavy enough (like in the tropics) to make the sands constantly wet. Thus, the accretion cycle can function properly as the precipitation provides the moisture needed for the vegetation to help store sand, and the sand is not constantly wet to stop the movement of it by the wind, but enough precipitation also comes to slow the Aeolian transport during some parts of the year.

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The atmosphere is a very important biophysical component in Coastal Dune Ecosystems. Wind, temperature,and precipitation are key climatic and weather factors that play a significant role in the moving of sand particles in the accretion cycle on Coastal Sand Dunes and in providing the conditions for the vegetation to grow.

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What is this habitat like?

Primary succession can happen when bare sand is colonised by plants. Over time, the sand builds up into sand dunes, raising the ground above the height of sea level. Succession in sand dunes is sometimes called a psammosere.

During the development of fixed dunes, younger embryo dunes are continually forming at the base of the dune system. As a result the dune system is advancing seaward.

Although succession takes place over time, different parts of a sand dune system can be taken to represent different stages of succession. If, for example, the sand dunes are advancing towards the sea at 1 metre per year, this means that the dunes at 100 metres inland will have been out of the water for 100 years. Of course, this assumes that the sand dunes are advancing at a constant rate, which may be contradicted by historical evidence.

Read more about the succession in sand dunes, or read on for investigation questions.

What questions do biologists ask?

You can ask many scientific questions about the sand dune environment. Here are some examples.

How many different plant species can be seen?

What are the key features of the dominant plant species?

What adaptations do plants have to help them survive in this environment?

How well does the soil here provide plants with what they need?

How does the microclimate affect the growth of plants here?

Is biodiversity highest at this seral stage?

How does grazing affect plants?

What is the impact of grazing on ecological succession?

Why is grazing useful for conservation?

Research question

Sub questions

Is primary succession happening at place x?

Does the distribution and abundance of vegetation change with distance from the sea shore? How and why do abiotic factors change with distance from the sea shore? What evidence is there of different seral stages?

How and why does the vegetation vary between two places in the dunes?
(e.g. seaward and landward faces of mobile dunes, dune ridge and adjacent dune slack, semi-fixed dunes compared to fixed dunes)

Does the distribution and abundance of vegetation change vary between the two places? How and why do abiotic factors vary? What adaptations do plants have in the two places?

What is the impact of human disturbance on the sand dunes at place y?
(e.g. tree felling, grazing by livestock, footpath erosion)

Does the distribution and abundance of vegetation change/vary between a disturbed and an undisturbed place (e.g. grazed vs ungrazed fixed dunes)? How and why do abiotic factors vary? What evidence is there for deflected succession?

What questions could you investigate with fieldwork?

Here are some examples. Each research question has been split into 2 or 3 sub-questions.

Adaptation

r and K strategies - pioneers are r-selected while climax plants are more K-selected

Transpiration and gas exchange

Xerophytic adaptations of many sand dune plants - surface area to volume ratio, density and location of stomata

Nitrogen cycle

Legumes with nitrogen-fixing bacteria in root nodules, free-living nitrogen-fixing bacteria in soil e.g. Azotobacter, ammonification by fungi and bacteria

Carbon cycle

Role of decomposers and detritivores in soil formation

Trophic levels and energy transfer

Role of chemoautotrophs and saprotrophs in sand dune soil
Primary productivity (NPP is highest before the climax community)

Photosynthesis

Limiting factors such as soil nitrogen

Conservation

Management of successsion for conservation, e.g. grazing

Synoptic links

A good investigation will make links between different parts of the A-Level Biology specification. Here are some possible synoptic links for investigations into sand dunes.

Succession in sand dunes

Where does the sand come from?

Sand is made up of fragments of rock that have been ground down by the sea. It is sometimes deposited by the sea in flat, sheltered parts of the coastline, like bays. As the tides recede, the free-draining sand deposited on the shore begins to dry out.

There are many ways in which sand can migrate inland, including saltation, traction and suspension.

Example: Saltation

If the shore faces into the prevailing wind, the sand grains will be blown inland. Single grains take to the air and hop about 6 metres; they land and dislodge a couple more grains of sand, which in turn take to the air and do the same. The process of wind-blown grains of sand jumping up the beach is called saltation. Sometimes you can see a cloud of sand moving up the beach in this way.

Stage 1: Migration

The sand grains move inland until they meet some form of obstruction. This might be a pile of seaweed dumped high up the shore by the sea, a lump of driftwood, a fence, a pool or muddy, sticky ground. Alternatively, sand might settle in the still air behind a small hillock or similar. At the top of the beach there is often a line of detritus deposited by the waves, known as the strand line, which marks the highest point that the sea reaches.

Sand grains moved by onshore winds can accumulate downwind of the strand line. Over time, a small embryo dune is formed. The embryo dune will grow if the rate at which soil is trapped is higher than the rate at which soil is blown away by the wind.

Stage 2: Colonisation

Plant seeds and spores are carried by the wind. Some of these land on the embryo dune, where they can germinate and develop. Colonisation means the growth of plants in a new place.

Physical conditions in embryo dunes are harsh. There is plenty of bare ground. The vegetation is described as "open", as there is lots of open space between plants. Plants that are able to grow in these harsh conditions are specialised to their environment, and are called pioneer species.

Embryo dune pioneer plant species include: Sand Couch ( Elytrigia juncea), Sea Sandwort ( Honckenya peploides), Sea Rocket ( Cakile maritima), Prickly Saltwort ( Salsola kali), Sea Mayweed ( Tripleurospermum maritimum) and Orache ( Atriplex spp.).

Pioneer plants at the strand line are highly stress-tolerant. Many have a tough outer layer, protecting the rest of the plant from abrasive sand-laden winds. There is little water available for the roots, as sand has a low moisture-holding capacity. Plants here are adapted to conserve moisture. Salinity (salt level) is high. Some pioneers have succulent leaves and stems, which are designed to store water and tolerate salinity.

As the pioneer plants grow and die, sand continues to accumulate, which raises the ground surface above the level of the highest tides. The death and decay of pioneer plants adds organic matter to the bare sand and increases its water holding capacity. The next plant to arrive is marram grass. The extensive root system of marram grass traps more sand, building the ground surface into a ridge of mobile dunes (also known as yellow dunes). The growth of marram grass is stimulated by burial in sand.

Stage 3: Establishment

Over time, the mobile dunes become less stressful for plants, as death and decay of vegetation continues to add organic matter to the soil. Vegetation cover becomes more continuous, with only a few small patches of bare sand, and this stage is called semi-fixed dunes. Tussocks of marram grass start to break up, as old marram growth is no longer being rejuvenated by burial in sand. Instead, a wider range of low-growing flowering plants are found.

Stage 4: Competition

The number of new species will be slowing down now. In fact the amount of free space is very limited and the chances are there will be few signs of bare sand. These are called fixed dunes.

The fixed vegetation surface prevents sand from moving as much as it did at the mobile dune stage.

Soil has become deeper, with a higher mositure content, higher humus content and lower pH.

The daily temperature range is smaller than in earlier stages. Where the sand is relatively alkaline (pH 6.0-7.5) because the sand contains a lot of shell material; the fixed dunes will be dominated by a continuous cover of grasses, sedges and low-growing flowering plants.

Where the sand is relatively acidic (pH 3.5-5.0), dune heathland may develop, with the arrival of woody shrubs such as heather and gorse.

In the development of the sand dune ecosystem, it is not uncommon for a dune slack to be created. This is when a blow-out (a damaged area of dune knocked back to bare sand by a combination of erosion and strong wind) takes the sand back below the level of the water table.

Dune slacks are variable in their nature. They will vary according to the frequency of inundation (which relates to the height of the blow-out floor relative to the summer/winter water table), the pH of the ground water and the substrate, the age of the slack, and the intensity of grazing.

If the dune slack is old enough then the community may develop to scrub, with willow ( Salix spp.), and moisture loving associates such as Marsh Pennywort ( Hydrocotyle vulgaris), Southern Marsh-orchid ( Dactylorhiza praetermissa), and various rushes and sedges.

Stage 5: Stabilisation

The next seral stage is characterised by the colonisation of woody plants such as brambles, sea buckthorn and small trees. Over time, a thick, sometimes acidic layer of humus develops. In these acidic dunes, the collapse of old heather bushes may provide a place for young birch trees to grow. This is known as dune scrub.

the climate of the area,

wind speeds and direction,

animal grazing and other management

pH

temperature

Stage 6: Climax

Shading by taller vegetation means that woody species out-compete species from earlier seral stages, and so the resulting species diversity is lower. The climax vegetation of sand dune succession is deciduous woodland. No new species are added and the community remains the same over long periods of time (theoretically forever). The vegetation is said to be in equilibrium with the environment; a true state of balance has been achieved. The type of climax vegetation present is determined by many factors including:

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Primary succession can happen when bare sand is colonised by plants. Over time, the sand builds up into sand dunes, raising the ground above the height of sea level. Succession in sand dunes is sometimes called a psammosere. During the development of fixed dunes, younger embryo dunes are continually forming at the base of the dune system.

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Learning in, learning about and learning for our natural environment

Sand dunes are one of the most at-risk habitats in Europe. There are often rare species living on the dunes therefore it is very important that they are managed in a way to ensure these species do not become extinct. On this page, you will find activity plans covering everything from why sand dunes are important to activities explaining how to carry out sampling on sand dunes.

All the activities and games on this page will help you enable your learners to progress in the ways described in the four purposes of the Curriculum for Wales. Curriculum links are included in the documents and all the activities will help you deliver many aspects of the cross curricular Literacy and Numeracy Framework (LNF) and Digital Competence Framework (DCF).

A guide to sand dunes

Want to learn about sand dunes? How they form, where they can be found in Wales and what is being done to restore them? Check out our information note.
Information note - Coastal sand dunes in Wales
Why are sand dunes important?

This activity plan highlights the importance of sustainably managing our natural resources, focusing on sand dunes and the multiple benefits they provide.

Activity plan - Why are sand dunes important? Resource cards - Why are sand dunes important?

How do sand dunes form?

These activities are intended to explain the process of sand dune formation in several different ways.
Activity plan - How do sand dunes form?
Resource cards - Sand dune formation - Sets A and B
A3 diagram - Sand dune formation - for use with Set A resource card
- Sand dune formation - for use with Set B resource cards
Resource cards - On your marks, get set, dune! Activity plan - Sand dune vegetation sampling
Worksheet - Sand dune vegetation sampling Information note - Marram grass
Activity plan - Marvellous marram
Activity plan - How do sand dunes form?
Resource cards (set A) - Sand dune super species
Resource cards (set B) - Sand dune super species Case study - Pembrey Burrows
Sand dunes super species

Our 'Activity plan - Characteristics of life and classification' will encourage your learners to investigate the characteristics of different species that live amongst sand dunes and consider how they can be classified.

The activities and games shared in 'Activity plan - Food webs and energy chains' are aimed at increasing learners' knowledge and understanding of sand dune food chains, energy transfer and relationships within a sand dune ecosystem.

Activity plan - Characteristics of life and classification
Activity plan - Food webs and energy chains

Resource cards - Both sets are used to complete several activities.

Resource cards (set A) - Sand dune super species Resource cards (set B) - Sand dune super species

Sand dune vegetation sampling

The aim of this activity is to give learners the opportunity to complete an onsite investigation into plant succession on a sand dune system and to prove or disprove a hypothesis. Suggested pre and post-visit activities are provided to maximise the learning opportunities a field visit to a dune system provides.

Marvellous marram grass

These activities enable learners to understand how marram grass root systems help to support sand dune development and how the species has adapted to the arid conditions of dune systems.

Sand dune and coastal processes glossary of terms

Don't know your climax vegetation from your climax community? Not a 'halophyte' what we are on about? Our glossary of terms explains all - this can be used as a go-to-guide or as a revision tool for learners.

Glossary - Coastal processes and sand dunes

Sand dunes through time - Newborough Warren

This activity explores people's relationship with sand dunes and how the natural resources they provide have been used over time.

Activity plan - Sand dunes through time - Newborough Warren Resource cards - Sand dunes through time - Newborough Warren

Case Study - Pembrey Burrows

An introduction to the management of Pembrey Burrows.

Campaigning for nature: Running a social media campaign

This activity plan sees learners take on the role of social media experts. They will be asked to plan, prepare, and potentially run a social media campaign to raise awareness of the issues affecting a specific sand dune system. From highlighting how it is being managed to encouraging visitors to help preserve and respect this valuable natural resource, this activity encourages learners to put their knowledge and understanding of sand dunes to work through their setting's social media platforms.

Activity plan - Campaigning for nature: Running a social media campaign- Campaigning for nature: Running a social media campaign PowerPoint presentation - Campaigning for nature: Running a social media campaign

Sands of LIFE

Learn more about the Sands of LIFE conservation project, aimed at revitalising sand dunes across Wales, by visiting the Sands of LIFE project webpage. The project will restore over 2,400 hectares of sand dunes at ten Welsh sites.

Contact us

If you can't find what you are looking for or would like any help or information, please contact us at:

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Sand dunes are one of the most at-risk habitats in Europe. There are often rare species living on the dunes therefore it is very important that they are managed in a way to ensure these species do not become extinct.

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Foredunes develop at the rear of the backshore environments (landward of the active beach) and generally comprise shore-parallel, convex, symmetrical to asymmetrical dune ridges. The morphology of foredunes is varied but they can be classified into three main types: incipient foredunes, established foredunes, and relict foredunes (Short & Hesp 1982, Hesp 2002).

Incipient foredunes are the initial dunes which accumulate above the high spring tide mark and form due to the presence of some roughness element at the rear of the beach that rapidly reduces wind flow velocities, resulting in sediment accumulation (Figure 1; Hesp 1999, 2002, Sloss et al. this issue). Driftwood sometimes forms the focus for the initial accumulation of dune sand, but vegetation is the most common roughness element that contributes to the formation of incipient dunes (Figure 1, photos 1-3). Incipient foredunes are sometimes ephemeral features, tending to be eroded or completely removed by severe storm events at irregular intervals varying from a few months to several years, but they may survive and grow to become a larger established foredune, or become relict and stable as a new incipient foredune develops to seaward (Hesp 1999, 2002).

Established foredunes (sometimes termed the "frontal dune") also originate at the landward edge of the beach, parallel to the shoreline. They develop from an incipient foredune and have a greater height, width, age, and/or morphological complexity (Hesp 2002). As an incipient foredune builds up, and out, sand inundation and salt spray levels decrease, while nutrient levels and vegetation cover increase, resulting in more stable dunes. The lee slope (i.e., the landward slope) is gradually often (but not always, depending on the latitude and coastal climate) colonised by a range of "woody" or shrub plant species that prefer more stable conditions (Hesp 1999, 2002). Sand is gradually deposited on the seaward slope, and sometimes the crest of the dune, which slowly becomes larger, forming an established foredune (Figure 1, photos 2-4).

Foredunes tend to be largest at the rear of dissipative beaches because of higher sand transport rates, but other factors may also influence foredune height. Particularly important is the length of time a foredune remains adjacent to the beach receiving windblown sand. If not eroded away or replaced seaward by a new foredune, elevations of 20 m or more may be reached, but the higher the dune the greater the wind shear and the greater the likelihood of blowouts (erosional saucer and trough-shaped hollows). Foredunes are lower where a coast has prograded (built seawards) rapidly. This is because the rapid growth of each new foredune to seaward cuts off the supply of windblown sand to the previous foredune before it can accrete (build upwards) to a significant height (Hesp 2002).

If the sediment supply is adequate, a new incipient dune may form seaward of the established foredune, resulting in the established foredune being relatively isolated from the sediment supply. The isolation of the dune, coupled with coastal progradation, can result in the development of successive foredunes that may eventually form a wide foredune plain (photo 5). This may consist of dozens to hundreds of relict foredune ridges, which are usually parallel with the coast and mark former shoreline positions (Hesp 2002). The best examples, with relatively unmodified ridges, are of Holocene age, while older Pleistocene dunes generally have a more subdued topography, with greater soil development and often indurated horizons.

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The size and morphology of coastal dunes is dependent on the complex interaction between controlling winds, sediment supply, and the geomorphology of the nearshore and beach environment. At the most basic level, dunes can be divided into those that form from the direct supply of sediment from the beach face (primary dunes), and those that form from the subsequent modification of primary dunes (secondary dunes).

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Sand dunes might sometimes look a bit bare, but there's plenty of life in even the most exposed areas of sand dunes!
Lovers of the bare sand include the sand lizard, who sunbathe in warm weather and hide in sandy burrows at night, and the beautiful northern dune tiger beetle who need sand to protect their larvae.

There's plenty hiding in the waters of the dune slacks, too. Natterjack toads will mate and leave their tadpoles to grow in slack ponds, joined by many different species of insect larvae and water-dwelling bugs.

What you might see in the dunes changes with the seasons; hundreds of wildflowers can carpet dry slacks during the spring, butterflies flit across areas of bare dune and low scrub in the summer, and grey seal pups are best spotted in the winter.

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How are sand dunes formed? Nature's process of building a sand dune is called succession. Sand dunes have a predictable lifecycle, with young and mobile dunes forming at the beach and old, stable dunes pushed further inland. Waves push sand up onto the beach, then the wind picks it up and moves it around the...

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Habitat Management

Maintain a full range of successional stages
Large dune systems should ideally have a full range of the successive stages of sand stabilisation: mobile foredunes with plants such as sand couch; dense marram clumps on young (yellow) dunes; grey dunes (surface of sand with grey lichens); more established dunes with varied vegetation; stable sandy grassland or dune heath and dune slacks. Some dunes also have streams or small rivers that provide habitat for a special invertebrate fauna.

Ground-nesting insects require bare and sparsely vegetated sand that is not excessively disturbed for nesting, plus a variety of other habitats for hunting and flower visiting. Maintaining flower-rich areas with plants such as scabious, Viper's bugloss and legumes will provide good foraging areas for populations of bees and other insects, which in turn will act as hosts for associated species such as Sarcophagid flies.

Any transitions with adjacent habitats such as saltmarsh, fen and woodland should be preserved. Such transitional areas are of great value to invertebrates and maintaining a range of vegetation types and sward heights will increase the range of habitat niches available. Any areas where the sand dune vegetation intergrades into a ruderal flora on the landward margins of the dunes are likely to support interesting ground beetles and bees.

Prevent excessive damage by disturbance and overuse by trampling
Many invertebrate species may be threatened by public pressure causing erosion and disturbance of the habitat. Management of public access is crucial to enable sensitive areas to be protected. Fences and boardwalks should be used where necessary to allow normal dune fixation and reduce disturbance from trampling. The establishment of a network of protected areas would greatly enhance the habitat quality of dunes where such pressure exists. Measures should not seek over-stabilisation of what should naturally be yellow dunes.

Sparse vegetation between sand couch and marram grass tussocks is especially rich in important invertebrate species such as leaf- and plant-hoppers, spiders and ground beetles. These fore-dunes are especially vulnerable to erosion and trampling, which should be kept to a minimum, if necessary fencing off areas periodically to allow recovery.

Use of dunes for dog walking can damage dune systems as a result of fouling by urine and excrement as well as increased trampling and car parking. Dune grasslands should also be protected from vehicle access, which can cause severe damage.

Ensure continuity of scrub and woodland
Scrub is an important habitat for some species and provides shelter and over-wintering sites for many dune invertebrates as well as being a good nectar source. A small amount of scrub consisting of native shrub species should be retained and managed so that it does not spread over large areas. However, many species, such as sea buckthorn can be aggressively invasive and need active management before their dense cover reduces the areas of bare sand and leads to drying of the site.

Many dunes have had associated woodland lost through development and what remains is often subject to high levels of disturbance. If native woodland is present, it is contributing to the overall habitat mosaic and should be treated as important. Dune slack carr, if present, can develop an interesting invertebrate community and should be retained. Excessive clearance of sallow scrub could be detrimental to many species; sallow catkins are important for early spring bees, moths and other insects.

Maintain dune slacks
Dune slacks are important for many scarce invertebrate species. The most valuable are those that are seasonally flooded in winter, but dry to mossy pools in the summer. This natural fluctuation should be allowed to continue and dune slack pools should never be deepened to make them permanent. The maintenance of high water tables in the area is important, and water abstraction or drainage of adjacent land should be resisted. Scrapes and pools should not be created on nearby land, as this can have the effect of drying and damaging the existing dune slacks.

Retain seepages, streams and brackish creeks
Any water flowing through or beside coastal dunes tends to be very interesting and should be viewed as an important component of the habitat. Similarly any areas of organically rich mud present within a dune system should not be cleared. The natural vegetation and sand banks along a stream system should be maintained; if necessary, marginal vegetation should be managed on a rotational basis to ensure continuity of invertebrate habitat.

Consider grazing or rotational management
Although grazing was traditionally used on many dune systems, this has greatly declined. If considering grazing, the needs of each individual site should be examined before implementation and objectives must include the implications for invertebrates since such a rich fauna is at stake.

For some invertebrate species, the maintenance of short grassland is important. Many species are associated with bare areas and grazing may be best in maintaining this Rabbit grazing tends to produced close-cropped lawns amongst taller vegetation and their scrapes provide areas of bare and disturbed ground that is required by species such as the endangered Sandbowl snail (Catinella arenaria). As long as the rabbit population does not increase to the extent that it is likely to threaten the stability of the dunes, eliminate a mosaic of varied vegetation structure or destroy important flower resources, rabbits should be viewed as a positive feature. Their dung and carrion also provide resources for many invertebrates.

Where rabbit populations have declined, sheep grazing may serve to provide areas of short grazed turf, but it is important to be vigilant that the site does not become over-grazed and lose structural diversity. Grasslands should retain patches of tussocky grasses and rushes and flower-rich areas, so rotational management of grazing stock may be necessary.

A cessation of long-established grazing should be avoided as populations of invertebrates such as the rare muscid fly Hydrotaea velutina may be dependent on a constant supply of dung. Dosing of livestock with broad-spectrum de-wormers which are damaging to insect development should be prevented. Abandonment of grazing can also lead to scrub invasion or dominance of sea buckthorn in fixed dune areas. However, grazing can be detrimental to other invertebrate species. Adults of the RDB cranefly Nephrotoma quadristriata have only been found in ungrazed areas of dune, and it is likely that close grazing by domestic livestock or rabbits could be damaging.

It is important to recognise that there is no management strategy that fits all dunes and that there are many dune sites that maintain their high invertebrate value in the absence of grazing. It is a case of 'if there is no problem, don't fix it'.

Retain biodegradable tidal debris
Tidal litter such as seaweed and driftwood found on the strandline provides essential shelter for many invertebrates and should not be cleared away as is often the case with beach tidying schemes. The removal of driftwood for beach barbecues or decorative purposes is highly damaging. The large, nationally scarce Beach comber beetle (Nebria complanata) requires fairly large items of flotsam such as driftwood under which to shelter and find the sandhoppers on which it feeds. The French zipper spider (Drassyllus lutetianus) also lives among wet tidal debris.

Avoid over-stabilisation of dunes
Dunes are dynamic features and blowouts are a natural and desirable feature of large dune systems, maintaining open conditions amongst areas of grassland and heath. Any dune stabilisation needs to be proportionate and to only go so far as to restore the natural conditions in the dune zone concerned. Coastal defences on site or even some distance away may interrupt sediment flow and thus the supply of sand necessary for continued accretion of dunes. Allowing coastal protection works to fall into disuse and even be actively removed may help restore natural processes, but careful assessment of outcome is first required.

Embryo dune development can be encouraged by the creation of sand trap high beach groynes, which collect wind blown sand on the foreshore. This is a potential means of building up natural defences where the sea is unduly eroding into the dunes, and is an option where the loss of pioneer vegetation zones and their fauna are threatened with elimination.

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Maintain a full range of successional stages Large dune systems should ideally have a full range of the successive stages of sand stabilisation: mobile foredunes with plants such as sand couch; dense marram clumps on young (yellow) dunes; grey dunes (surface of sand with grey lichens); more established dunes with varied vegetation; stable sandy grassland or dune heath and dune slacks.

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Sand dunes are places of constant change and movement. Wander through them on warm summer days for orchids, bees and other wildlife, or experience the forces of nature behind their creation - the raw power of a winter storm.