Review of Efforts to Combat Desertification and Arrest and Reverse Land Degradation in Myanmar - Combating Desertification in Asia, Africa and the Middle East - page 276

and fauna, as well as the secondary consequences of water and wind erosion and
other forms of soil degradation that will be an eventual result of the reduced or
impoverished vegetative cover.
Deforestation is here taken to mean the large-scale removal or partial removal
of trees from forested areas, which may be deliberate or due to natural causes. De-
liberate causes of deforestation include commercial logging, firewood production,
clearing for agricultural or timber plantation purposes, “slash and burn” techniques
of shifting agriculture, and clearing for such purposes as urban development or the
development of infrastructure such as dams, road, railways or mining facilities.
Natural causes of deforestation include wild fire, predation by a variety of pests
and parasites, disease, damage by pest animals or grazing animals and human traffic
or occupation. Forests shield the soil surface from heavy rainfall, reduce the rate
of run-off by increasing the rate of infiltration and as a consequence decrease the
amount of flooding, mitigate soil erosion and limit the sedimentation of rivers. They
can also act to control landslides and other forms of mass movement of the land
surface.
On the other hand, deforestation of watersheds, especially around smaller
rivers and streams, can increase the severity of flooding, reduce stream flows by
lowering the watertable and increase sedimentation of rivers. Accelerated erosion,
soil salinization and impairment of water quality are other common adverse
consequences of deforestation. These secondary forms of degradation and ways and
means for controlling or mitigating them will be discussed in some detail in other
sections of this chapter. The factors contributing to deforestation can all adversely
affect land and water resources. The loss of protective tree cover has resulted in
erosion, landslides and the silting of rivers and dams, as well as increased flooding
downstream. The loss of trees also results in reduced organic matter and the loss of
nutrients from the soil by leaching. This leads to further degradation of the quality
and extent of forest cover. The destruction of trees on steep slopes and along the
banks of rivers and streams can significantly increase erosion and sedimentation
problems in the lowland areas of watersheds. In the Asia Pacific region, the rate
of deforestation is a major factor contributing to watershed degradation and the
increased severity of water related natural disasters. Until comparatively recently,
the rate of deforestation in areas of forest has been a cause for much national and
international concern.
Land clearing is here taken to mean the large-scale removal of vegetation from
woodlands, shrublands and grasslands in order to use them for such purposes as
grazing, cropping or irrigation development. This form of activity is practiced in
low to marginal rainfall areas where the climatic and soil conditions are not suitable
for forest growth but there is potential for large-scale crop or livestock production.
As with deforestation, the removal of vegetation makes the land susceptible to water
erosion and wind erosion, the latter in particular being a major potential problem in
arid and semi-arid areas. Other associated adverse effects may be various forms
of soil degradation as a consequence of cropping or irrigation practices, as well as
potential invasion and damage by pest species. As is also the case with deforestation,
extensive land clearing involves a loss of ecosystem productivity and diversity