• 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.

• 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.

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.

• 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.