Decline in vegetation cover/biomass

Decline in vegetation cover

Vegetation cover is key factor on land degradation. Reduction in the perennial cover is regarded as an important indicator of the onset of desertification. Vegetation cover plays very important role on protecting the soil surface from raindrop splashing, increasing soil organic matter, soil aggregate stability, water holding capacity, hydraulic conductivity, retarding and reducing surface water runoff, etc. Many authors demonstrated that in a wide range of environments, both water run-off and soil sediment loss decrease exponentially as the percentage of vegetation cover increases. 

Many authors have demonstrated that in a wide range of environments, both run-off and sediment loss decrease exponentially as the percentage of plant cover increases. A value of 40% vegetative cover is considered the critical threshold below which accelerated erosion dominates in a sloping landscape. This threshold may be modified for different types of vegetation, rain intensity and land attributes. In the case of poor plant cover, the erosion processes may be very active and the regeneration of natural vegetation may be irreversible.

Soil erosion and degradation begins only when a substantial portion of the land's surface is denuded of vegetation, then it proceeds with an accelerated mode, that cannot be arrested by lands resistance alone. Deep soils on unconsolidated parent materials show slow rates of degradation and loss of their biomass production potential. In contrast, shallow soils with lithic contact on steep slopes have low productivity, and low erosion tolerance if they are not protected by adequate vegetation. Soil and vegetation survey data from the island of Lesvos clearly indicated that the percentage plant cover was greatly affected by the soil depth in the various climatic zones. Vegetation cover increased with increasing soil depth and decreasing longevity of drought. In the soil depth class of 15-30 cm, the vegetation cover class of 25-50% had the maximum frequency of appearance (93%) in the semi-arid zone, whereas areas with soils having the same soil depth class had a higher vegetation cover with a 64% maximum frequency of appearance of the cover class 75-90% cover in the dry sub-humid zone. Soil erosion measurements conducted in eastern Spain showed that soil erosion rates for bare soils ranged from 0 to 3720 g m-2 h-1, while the densely vegetated soils show negligible runoff and erosion.