Page 42 - Soil Degradation, Conservation and Remediation

1.7 Soil Degradation 27

The FAO analysis concludes that the leading causes of deforestation are the
extension of subsistence farming (more common in Africa and Asia) and
government- backed conversion of forests to other land uses such as large-scale
ranching (most common in Latin America and also Asia). Poverty, joblessness, and
inequitable land distribution, which force many landless peasants to invade the
forest for lack of other economic means, continue to drive forest clearance for
subsistence farming in many regions. Often, people move into forest areas as log-
ging activity creates roads that open formerly inaccessible regions. As for centrally
planned forest conversion schemes, these are often used to spur short-term economic
development, gain better political control of remote forest regions, and expand agri-

cultural output (FAO 2000 ). Geist and Lambin ( 2001 ) have identified a host of
causes for tropical deforestation. It is increasingly evident that a concentration of
variables interacts across spatial and temporal scales (Turner et al. 2001 ). In Latin
America, small farmer agricultural expansion along forest frontiers is probably the
primary proximate cause of forest clearing, followed by in situ agriculture and pas-
ture expansion, timber felling for fuel and construction, and infrastructure expan-
sion. In Africa, a greater proportion of deforestation come from sedentary
(non-frontier) agricultural expansion and fuel wood harvesting. In Asia, deforesta-
tion continued due to increasing demands on timber resources and continued migra-
tion of shifting farmers to remote areas.
Deforestation processes include industrial logging, clear felling, indiscriminate
cutting, forest fires, shifting cultivation, and encroachment. The effects of deforesta-

tion are loss of forest, loss of biodiversity, climate change, and natural disasters such
as cyclones, flood and drought, disruption of water cycle, decline in water quality,

soil erosion, and sedimentation. Forests regulate the hydrologic processes: evapora-

tion, transpiration, infiltration, and surface flow. Cutting trees in large tracts results

in the climate getting drier in that area. Forest clearance exposes the bare soil to the

scorching effect of the sun and the beating action of the rains. Significant amount of
top soil is lost by erosion. Due to elevated temperature, soil organic matter is decom-
posed at a faster rate, and soil aggregates are broken down by raindrop impact.

Infiltration rate is reduced and more water runs off. Large tracts of land become
permanently impoverished due to soil erosion for these reasons. Deforestation
increases the carbon dioxide emission into the atmosphere. Tropical deforestation
accounts for about 20 % of total global carbon dioxide (CO 2 ) emissions (IPCC
2007 ).
Global Climate Models (GCM) may show that tropical deforestation would
affect both small-and large-scale climate in the tropics (Zhang et al. 1996b ). Results
have further indicated that impacts of tropical deforestation depend upon regional
climate characteristics in the tropics where disturbances are imposed (Mylne and
Rowntree 1992 ; Polcher and Laval 1994 ). Tropical deforestation contributes to the
increasing atmospheric carbon dioxide burden and hence the warming of climate
(Houghton et al. 1996 ). Forests occupy an important position in the hydrological
cycles of watersheds. Water evaporates from the soil and vegetation, condenses into
clouds, and falls again as rain in a perpetual self-watering cycle. In addition to main-
taining tropical rainfall, the evaporation cools the earth’s surface. In many computer