Changes in intensity of wind erosion at different stages of degradation development in grasslands of Inner Mongolia, China

Abstract

Overgrazing by increasing numbers of livestock in the Horqin Sandy Land of Inner Mongolia, China, has led to extensive degradation of the region's sandy steppes. Degraded grasslands are generally classified into four main types: fixed (least degradation), semi-fixed (light degradation), semi-shifting (moderate degradation) and shifting (severe degradation) sandy lands, representing four stages of degradation development. An experiment was conducted in the Horqin Sandy Land to investigate changes in intensity of wind erosion at different stages of degradation development in sandy grasslands and determine the extent to which surface wind erosion was affected by surface-related soil and vegetation factors through their effects on surface roughness length and wind regimes. Daily wind erosion rate was monitored at four sites of degraded grassland over an erosive period from 1 April to 10 June in 2001. Soil and vegetation properties for these sites were also measured twice: one in mid-April prior to the establishment of vegetation and again in mid-June after the establishment of vegetation. Relationships between surface roughness length and soil and vegetation variables were examined at each of the two stages of vegetation development. This study shows striking differences in the intensity of surface wind erosion among sites. The daily wind erosion rate in the fixed sandy land was, on average, only about 1/5 of the rate in the semi-fixed sandy land, 1/14 of the rate in the semi-shifting sandy land and 1/47 of the rate in the shifting sandy land suggesting a much higher resistance of the fixed sandy land to wind erosion compared to other sites. Differences in rate of wind erosion between sites were attributed to between-site differences in soil and vegetation properties that exerted significant effects on wind regimes by altering surface roughness length. At the pre-establishment stage of vegetation, surface roughness length was determined by a combination of litter amount on the ground, soil surface hardness and soil moisture content, with litter amount explaining the greatest proportion of the variation. At the post-establishment stage of vegetation, the development of the surface roughness effects was mainly governed by vegetation characteristics (vegetation cover in particular), while the effects of soil surface hardness and soil moisture on surface roughness length are likely to be masked by vegetation effects. The findings suggest that better management practices of restoring vegetation in degraded grasslands are required to reduce soil erosion losses and achieve a sustainable livestock production in the Horqin Sandy Land, an ecologically fragile sandy land ecosystem.