For decades, arid desert ecosystems in northwest China, covering one-fourth the country's land surface, have experienced a rapid decline in plant species diversity, productivity and soil carbon stock owing to degradation by overgrazing. In this study, plant community composition, diversity and productivity, as well as soil carbon (C) and nitrogen (N) stocks, were monitored over 26 years from 1981 to 2006 in a severely degraded Haloxylon ammodendron-dominated shrubland where livestock densities were reduced from 4-5 to 1-2 dry sheep equivalent ha -1 . The objective was to assess long-term grazing effects on vegetation and soil C and N accumulation dynamics. Results showed that the reduction of grazing pressure significantly increased vegetation cover, plant diversity and productivity, resulting primarily from an increase in livestock-preferred species. Controlled grazing also led to marked increases in soil C and N stocks in the top 30 cm of soil. This increase was strongly associated with increased plant species richness, vegetation cover and biomass production. Averaged over 26 years, soil C and N accumulated at rates of 89.9 gC and 8.4 gN m -2 year -1 , respectively, but rates of C and N accumulation varied greatly at different time periods. The greatest species regeneration occurred in the first 8 years, but the largest C and N accumulation took place during years 9-18, with a time-lag in response to changes in vegetation. Our results provide insights into the long-term recovery patterns of different ecosystem components from the influence of prolonged overgrazing disturbance that cannot be inferred from a short-term study. The findings are important for assessing the resilience of these livestock-disturbed desert ecosystems and developing a more effective strategy for the management of this important biome from a long-term perspective.

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Soil desertification is a serious problem in arid northwestern China that threatens ecological sustainability. Artemisia sphaerocephala, a dominant shrub species, play an important role in the conservation of water and the restoration of soil in the desert ecosystem. However, the poor establishment of A. sphaerocephala often limits plant revegetation, and the optimal population density for sustainable growth is largely unknown. Here, we determined key soil properties and plant growth characteristics associated with different population densities of A. sphaerocephala (including from 1.1, 2.1, 3.1, 3.9 to 5.3 plants per m2) in the resource-limited Alashan desert of northwestern China. The results showed that plant population density was the primary factor determining the revegetation of A. sphaerocephala, followed by soil water availability. Soil N, P and K content, and soil fractal dimensions also contributed to the vegetation and productivity. Soil nutrients were mostly accumulated in the topsoil layers, coincidental with the root distribution pattern in which 57% to 82% of total roots were distributed in the top 20 cm soil layer. The concentrations of soil nutrients in higher population densities (3.9 to 5.3 plants per m2) were greater than those in lower population densities (1.1 to 2.1 plants per m2), suggesting that A. sphaerocephala may have the ability to promote nutrient cycling in the desert ecosystem. We conclude that the optimal population density for the best growth of revegetated A. sphaerocephala was 3 plants per m2.

This chapter discusses the mechanisms of soil erosion by wind and water in rangelands, including natural and other factors influencing soil erosion processes, especially human activities. Finally, a review of available desertification control technologies in north China, including biological, engineering and chemical methods, is introduced.