Land degradation and mitigation in northern China. Evaluated from the biological production

Abstract: Land degradation is commonly perceived to be severe in many parts of semi arid China. The transition towards market economy since the 1978 reforms, have set marginal dry lands under added pressure in the form of increased livestock numbers and expanding cultivation on erosive soils. To evaluate land degradation since the reforms, this study focuses on mapping and analysing the biological production of the Mu Us Shamo on the Ordos Plateau in the Inner Mongolia Autonomous Region (IMAR). Time series of satellite data are examined for analysing the seasonal dynamics of biological production, annual variability and trends. Images with high geometric resolution are used to study the small-scale changes in land use and vegetation cover. A Light Use Efficiency (LUE) model is further adapted to the steppe regions of the IMAR. The model is driven by NOAA AVHRR and climate data, producing monthly estimates of Gross Primary Production (GPP) from 1982 through 1999. Although there have been rapid increases in livestock numbers, the trend of GPP since 1982 is generally positive. The annual variability of GPP is high resulting from the erratic monsoon climate. In Wushen Banner, a central county in the Mu Us Shamo, the area indicating improved vegetation cover between 1987 and 1996 is nearly ten times that of declining vegetation cover. The area of cultivation expanded almost five-fold, to about 2% of the county area, of which, nearly all is irrigated. No abandoned farmland could be detected, indicating short-perspective strategies from intensive farmland reclamation. Severe degradation causing declining biomass production rates and expansion of the desert area cannot be drawn from this investigation. Re-vegetation activities to mitigate land degradation such as the Green Wall, farmland lee-shelters, aerial seeding etc., are likely to be contributing to the increase in biological production in this region, and may act as a balance to the increased utilization of these pastures.