When the ground is free from litter and cover, water flows freely and can take away the soil with it.
Living forests play the opposite role, removing carbon dioxide from the atmosphere. Atmospheric circulation and rainfall patterns are then significantly altered.
This is why large areas of formerly productive land, where annual rainfall is relatively high, have become desertified once tree cover is removed.
A dense and vigorous pasture will reduce sheet and wind erosion, but its shallow roots do not prevent slips, gullies and slumping. References http: Soil is protected under tree cover because of the litter — the leaves and branches that our shed by the tree and fall to the ground.
The entire Himalayan region is prone to soil loss. Furthermore, in deforested areas, much less solar energy is used to evaporate moisture from the leaves of plants and trees. Waterlogged soil becomes saline as water is repeatedly evaporated from its surface, leaving salts behind and concentrating them near the soil surface. The destruction of forests upstream affects the flow of these rivers and the amount of sediment they carry, and therefore increases the magnitude of flooding downstream.
Such salt breaks also offer protection against wave damage during storms, and reduce the chances of flooding and physical damage to inland areas from tide surges.
In parts of Indonesia, reforestation has reduced sedimentation rates in downstream valleys by as much as two-thirds. Sheep were replaced by beef cattle, which do not graze as closely, so they expose the pasture to rabbit invasion.
In arid and semi-arid parts of the world trees are used to slow down the expansion of the deserts and stabilize sand dunes so that crops can be grown. The importance of these effects has often been ignored in the past, with the clearance of tree vegetation and the subsequent loss of millions of hectares of productive land.
Thousands have also been planted throughout the North Island hill country. The establishment of woody perennials and nitrogen-fixing trees close to, or intercropped with, agricultural crops maintains or improves the fertility of arable land.
Poplars are fast growing and their root systems develop rapidly. Radiata pine Pinus radiata and macrocarpa Cupressus macrocarpa are the most widely used species.
Often these areas are the headwaters of large watersheds. And just as important, they help to hold the soil around the tree. Planting trees on land that is badly compacted may help break up the soil structure and so improve the rate at which rainfall infiltrates the soil.