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Changes to forests

Around the world about 5 million hectares of forest is converted for agricultural use every year: an area about two-thirds the size of Tasmania.

Most changes takes place in tropical forests, particularly in South America and Africa.

Few forests in regions have been converted to farmland because most of the forests have disappeared.

Changes to grasslands

The clearing of native grasses to plant crops can have devastating effects on the natural environment.

This farming can lead to the soil fertility to fall.

This means farmers need to add chemical fertilisers to the soil, which further changes its composition.

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soil degradation

in many places around the world, soils are degrading.

it is estimated that about 2 billion hectares of land have been affected my this.

salinity

in Australia,soil degradation often takes the form of salt salinity

salinity is a condition where the amount of salt causes problems in the soil.

primary salinity

secondary salinity

terracing

the shape of the land

soil can be altered through terrace farming.

terracing does not always have a negative impact on the landscape

types of terracing

bench-terracing, contour-terracing, and parallel-terracing.

the purpose of terracing

prevent rainfall runoff on sloping land from accumulating and causing serious erosion.

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What causes expanding deserts?

Climatic variations and Human activities

What it affects

this affects millions of people around the world

Desertification is a type of land degradation where once productive and thriving land transforms into dry desert landscapes.

hard for farm land

Desertification is a type of land degradation where once-productive and thriving land transforms into dry, desert landscapes.

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Water pollution from farming

The water that is used on farms eventually flows through soil and rocks into nearby streams and rivers.

The bare soil that is not protected by plants and held together by their roots can be washed away in the process

causes streams to become so cloudy that sunlight cannot reach the stream bed.

This often kills many aquatic plants and animals.

Fertilisers can end up in lakes and rivers, causing algae to grow out of control.

Changing natural water flows

Rivers are dammed to create large reservoir of water which can be used for irrigation.

Most of the water is used for farming.

The reduce volume of water in the rivers creates major problems for the natural environment and for downstream users.

Water can be 5 times saltier than the sea.

This is because so much water has been extracted for farming that the river cannot flush out the naturally occurring salt.