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desert, any large, extremely dry area of land with sparse vegetation. It is one of Earth's major types of ecosystems, supporting a community of distinctive plants and animals specially adapted to the harsh environment. For a list of selected deserts of the world, .

Desert environments are so dry that they support only extremely sparse vegetation; trees are usually absent and, under normal climatic conditions, shrubs or herbaceous plants provide only very incomplete ground cover. Extreme aridity renders some deserts virtually devoid of plants; however, this barrenness is believed to be due in part to the effects of human disturbance, such as heavy grazing of cattle, on an already stressed environment.

According to some definitions, any environment that is almost completely free of plants is considered desert, including regions too cold to support vegetation-i.e., "frigid deserts." Other definitions use the term to apply only to hot and temperate deserts, a restriction followed in this account.

Origin

The desert environments of the present are, in geologic terms, relatively recent in origin. They represent the most extreme result of the progressive cooling and consequent aridification of global climates during the Cenozoic Era (65.5 million years ago to the present), which also led to the development of savannas and scrublands in the less arid regions near the tropical and temperate margins of the developing deserts. It has been suggested that many typical modern desert plant families, particularly those with an Asian centre of diversity such as the chenopod and tamarisk families, first appeared in the Miocene (23 to 5.3 million years ago), evolving in the salty, drying environment of the disappearing Tethys Sea along what is now the Mediterranean-Central Asian axis.

Deserts also probably existed much earlier, during former periods of global arid climate in the lee of mountain ranges that sheltered them from rain or in the centre of extensive continental regions. However, this would have been primarily before the evolution of angiosperms (flowering plants, the group to which most present-day plants, including those of deserts, belong). Only a few primitive plants, which may have been part of the ancient desert vegetation, occur in present-day deserts. One example is the bizarre conifer relative welwitschia in the Namib Desert of southwestern Africa. Welwitschia has only two leaves, which are leathery, straplike organs that emanate from the middle of a massive, mainly subterranean woody stem. These leaves grow perpetually from their bases and erode progressively at their ends. This desert also harbours several other plants and animals peculiarly adapted to the arid environment, suggesting that it might have a longer continuous history of arid conditions than most other deserts.

Desert floras and faunas initially evolved from ancestors in moister habitats, an evolution that occurred independently on each continent. However, a significant degree of commonality exists among the plant families that dominate different desert vegetations. This is due in part to intrinsic physiologic characteristics in some widespread desert families that preadapt the plants to an arid environment; it also is a result of plant migration occurring through chance seed dispersal among desert regions.

Such migration was particularly easy between northern and southern desert regions in Africa and in the Americas during intervals of drier climate that have occurred in the past two million years. This migration is reflected in close floristic similarities currently observed in these places. For example, the creosote bush ( Larrea tridentata), although now widespread and common in North American hot deserts, was probably a natural immigrant from South America as recently as the end of the last Ice Age about 11,700 years ago.

Migration between discrete desert regions also has been relatively easier for those plants adapted to survival in saline soils because such conditions occur not only in deserts but also in coastal habitats. Coasts can therefore provide migration corridors for salt-tolerant plants, and in some cases the drifting of buoyant seeds in ocean currents can provide a transport mechanism between coasts. For example, it is thought that the saltbush or chenopod family of plants reached Australia in this way, initially colonizing coastal habitats and later spreading into the inland deserts.

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Desert | Definition, Climate, Animals, Plants, & Types

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Desert, any large, extremely dry area of land with sparse vegetation. It is one of Earth's major types of ecosystems, supporting a community of plants and animals specially adapted to the harsh environment. In deserts, trees are usually absent, and shrubs or herbaceous plants provide only very incomplete ground cover.

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Thick forests found in wet areas of the world are called rainforests. Most people are familiar with hot, tropical rainforests filled with trees that stay green year-round....

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Some mountains form when the big slabs of rock-called tectonic plates-that make up the Earth's crust crash into each other. Over millions of years, the sheets of rock push up and over one another, creating the mountain. Others form when vents in the Earth's surface erupt and spew lava out onto the ground. The lava piles up and cools. Over millions of years, the many layers of hard lava become a mountain.

Mountains are on every continent. The longest mountain range is over 40,000 miles long-and 90 percent is under the ocean! Called the Mid-Ocean Ridge, it wraps around the globe like the seams of a baseball. The longest aboveground mountain range is the Andes. Running along the entire west coast of South America through seven different countries-including Argentina, Chile, and Colombia -it's 4,700 miles long.

Mount Everest, on the border of Nepal and China in Asia, is the highest mountain above sea level in the world. Towering at just over 29,000 feet it would take almost 5,000 grown men stacked on top of each other to reach that high.

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Making Mountains Some mountains form when the big slabs of rock-called tectonic plates-that make up the Earth's crust crash into each other. Over millions of years, the sheets of rock push up and over one another, creating the mountain. Others form when vents in the Earth's surface erupt and spew lava out onto the ground.

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LOCATION: Wetlands are areas where standing water covers the soil or an area where the ground is very wet. Unlike estuaries, freshwater wetlands are not connected to the ocean. They can be found along the boundaries of streams, lakes, ponds or even in large shallow holes that fill up with rainwater. Freshwater wetlands may stay wet all year long, or the water may evaporate during the dry season.

There are many different types of freshwater wetlands, all of which have different names. This can sometimes lead to confusion. These are all names of different types of wetlands: marsh, bog, fen, swamp, mire, slough, and prairie pothole. These places can look very different, but because they are all areas with wet soil, or where water covers the soil, they are considered wetlands.
More information on these different types of wetlands
PLANTS: Freshwater wetlands have a variety of plant types, and each different type of wetland may have different kinds of plants. The plants discussed here are fairly common. There are floating plants, such as duckweed, that extends its roots down into the water to absorb nutrients. The duckweed floats freely and is not attached to the bottom. Cattails and sedges are common plants that grow up from the soil, through the water.

ANIMALS: As with plants, the types of animals found in wetlands depend upon the type of wetland. There are, however, some general types of animals that will be found in most wetlands.

All kinds of amphibians (frogs, toads and salamanders) can be found. Amphibians require water in which to lay their eggs and for the tadpoles to grow to adulthood. Wetlands are a perfect environment for this. In fact, when visiting wetlands, one of the first things you a may hear are the calls of frogs. Sometimes, especially during the mating season, they can be so loud it's hard to hear anything else.

Insects are an important part of the plant and animal life in wetlands. They help to pollinate plants and provide food for birds and amphibians. Watch out for the mosquitoes! You may want to bring your insect repellent when visiting a wetland because mosquitoes thrive in areas of standing water.

Feel like taking a swim in a wetland? Before you jump in or even wade through the water, you may want to consider another wetland animal with a bad reputation: leeches. Most leeches prefer environments with standing water, making freshwater wetlands a perfect home. They feed by latching onto another animal or a human and sucking their blood. You often can't feel them when they latch on and so may be surprised to look down and find yourself being eaten for lunch. Leeches aren't all bad. Doctors use them to help with blood clots and to improve circulation to areas of the body after surgery.

Wetlands are also home to an amazing number of birds. Many birds would go extinct without wetland habitat in which to breed, build nests, raise young, feed and rest along migratory routes.

PEOPLE AND FRESHWATER WETLANDS: Freshwater wetlands, like estuaries, provide very valuable services to people. They provide fish to eat and flood protection during storms. They also filter our water, giving us clean water to drink. Because of these valuable services, it is important that we work to conserve our wetlands.
LINKS: Wetlands 101 What is a Wetland? U.S. EPA - America's Wetlands California Wetlands Information System Australian Museum - Animals of Freshwater Habitats Natural History of Nova Scotia - Freshwater Wetlands Habitats
Back to Biomes Index

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LOCATION: Wetlands are areas where standing water covers the soil or an area where the ground is very wet. Unlike estuaries , freshwater wetlands are not connected to the ocean. They can be found along the boundaries of streams, lakes, ponds or even in large shallow holes that fill up with rainwater.

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There's something magical about walking through a forest. It's usually quiet and a bit dark. The air smells musty and earthy. You might feel like you're the only person on earth.

Forests are found on almost every continent in the world. Not only are they beautiful, but they provide shelter for animals and wood for humans. Forests also clean the air.

Fun Facts about Forests for Kids

Deciduous forests have trees that lose their leaves in the fall. These trees have four layers - very tall trees like oaks, smaller trees and saplings, shrubs and bushy plants, herbs and small ground plants and finally the ground layer, which includes mosses and lichens.

Many plants and animals live in forests. Many animals hibernate in the winter.

Some forests are plantation forests. These are forests that have been planted by tree farmers. The plantations supply much of the wood humans use.

Some forests have evergreen trees, such as pine trees. These trees don't lose their leaves, or needles, in the winter.

Redwood trees growing in the Redwood forest in northern California can grow more than 350 feet tall. Average skyscrapers are about this tall. Some of these trees are 2,000 years old.

Forest Vocabulary

Learn More All About Forests

Understand more about forests in this video:

A video about various facts of the forests

Forest Q&A

Question: Do edible plants grow in the forest?

Answer: Many edible plants, berries and mushrooms grow there. Don't eat them though unless a grownup says it's okay. Many plants are poisonous.

Enjoyed the Easy Science for Kids Website all about Forests info? Take the FREE & fun Forests quiz and download FREE Forests worksheet for kids. For lengthy info click here.

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There's something magical about walking through a forest. It's usually quiet and a bit dark. The air smells musty and earthy. You might feel like you're the only person on earth. Forests are found on almost every continent in the world. Not only are they beautiful, but they provide shelter for animals and wood for humans.

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Tundra ecosystems are treeless regions found in the Arctic and on the tops of mountains, where the climate is cold and windy, and rainfall is scant. Tundra lands are covered with snow for much of the year, but summer brings bursts of wildflowers.

Plants and animals in tundras

Mountain goats, sheep, marmots, and birds live in mountain-or alpine-tundra and feed on the low-lying plants and insects. Hardy flora like cushion plants survive in the mountain zones by growing in rock depressions, where it is warmer and they are sheltered from the wind.

The Arctic tundra, where the average temperature is -30 to 20 degrees Fahrenheit (-34 to -6 degrees Celsius), supports a variety of animal species, including Arctic foxes, polar bears, gray wolves, caribou, snow geese, and musk oxen. The summer growing season is just 50 to 60 days, when the sun shines up to 24 hours a day.

The relatively few species of plants and animals that live in the harsh conditions of the tundra are essentially clinging to life. They are highly vulnerable to environmental stresses like reduced snow cover and warmer temperatures brought on by global warming.

Climate change impact on tundras

The Arctic tundra is changing dramatically due to global warming, a term that falls within a wider range of trends scientists now prefer to call climate change. The impacts in this region are broad and somewhat unpredictable. Animals that are typically found further south, like the red fox, are moving north onto the tundra. This means the red fox is now competing with the Arctic fox for food and territory, and the long-term impact on the sensitive Arctic fox is unknown.

Other tundra denizens, such as the wolf spider, are growing bigger and thriving. Shrubs are getting taller, contributing to declines in the sensitive groups of lichen that caribou and other species depend on for food. Lakes and ponds are evaporating or draining away.

Perma defrost

The Arctic's permafrost, the literal foundation for much of the region's unique ecosystem, is deteriorating with the warmer global climate. Permafrost is a layer of frozen soil and dead plants that extends some 1,476 feet (450 meters) below the surface. In much of the Arctic, it is frozen year-round. In the southern regions of the Arctic, the surface layer above the permafrost melts during the summer, and this forms bogs and shallow lakes that invite an explosion of animal life. Insects swarm around the bogs, and millions of migrating birds come to feed on them.

With global warming, the fall freeze comes later- in some places recently, not at all-and more of the permafrost is melting in the southern Arctic. Shrubs and spruce that previously couldn't take root on the permafrost now dot the landscape, potentially altering the habitat of the native animals.

Another major concern is that the melting of the permafrost is contributing to global warming. The frozen ground contains about one and a half times the amount of carbon already in the atmosphere today, as well as large amounts of methane, another potent greenhouse gas. Until recently, the tundra acted as a carbon sink and captured huge amounts of carbon dioxide from the atmosphere as part of photosynthesis. That process helped keep the amount of this greenhouse gas from accumulating in the atmosphere.

Today, however, as the permafrost melts and dead plant material decomposes and releases greenhouse gases, the tundra has flipped from a carbon sink to a carbon contributor. That means not only is the planet less capable of preventing greenhouse gases from accumulating, but the tundra is also contributing to their buildup. Scientists are still learning about what else the permafrost harbors, and what could be released as it thaws. Recently a study found that it is also the largest store of mercury on the planet and could release the toxic heavy metal into the environment, to harmful effect.

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Tundra ecosystems are treeless regions found in the Arctic and on the tops of mountains, where the climate is cold and windy, and rainfall is scant. Tundra lands are covered with snow for much of the year, but summer brings bursts of wildflowers.

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Desert Animals and Plants | Desert Ecosystem | Desert Video for kids

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It's Our Forest - Part 1 Forest EcoSystem

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Fabulous Wetlands with Bill Nye The Science Guy (1989)

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Fabulous Wetlands with Bill Nye The Science Guy (1989)

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Grasslands are common on every continent but Antarctica, yet they're far from predictable.