Developing stages and causes of desertification in the Mu Us sandland

Based on historical aerial photography of three periods and together with field investigation, the status of desertification development after the 1950s in the Mu Us sandland was analyzed, the difference of the desertification developing speed at two stages was compared, and its possible causes were explored. The results show that the developing speed of desertification from the late 1970s to the early 1990s is apparently slowed down, compared with that from the late 1950s to the late 1970s and there exists an obvious recovery trend at the second stage. The difference between the two stages accounts for severely over-reclaiming, over-grazing and unrestricted cutting during the first stage, which are the main causes of desertification development in the semi-arid steppe and arid desert steppe areas.

Effects of Seasonal and Perennial Grazing on Soil Fauna Community and Microbial Biomass Carbon in the Subalpine Meadows of Yunnan, Southwest China

Grazing and over-grazing may drive changes in the diversity and functioning of below-ground meadow ecosystems. A field soil survey was conducted to compare microbial biomass carbon （Cmin） and soil fauna communities in the two main grassland management systems in subalpine regions of Yunnan Province, China： perennial grazing currently practiced due to increasing herd sizes and traditional seasonal grazing. A three-year exclosure experiment was then conducted to further compare the effects of different grazing practices, including treatments of no mowing, perennial grazing （NM ＋ G）, mowing followed by seasonal grazing （M ＋ G）, mowing and no grazing （M ＋ NG）, and no mowing or grazing （NM ＋ NG）. The comparative survey result revealed that Cmin and total density of soil fauna were significantly lower at a perennially grazed site than at a seasonally grazed site. The experiment results showed that in comparison to non-grazing treatments （M ＋ NG and NM ＋ NG）, grazing （NM ＋ G and M ＋ G） reduced total fauna density （by 150 individuals m-2） and the number of taxonomic groups present （by 0.32 taxa m-2）. Mowing decreased Cmin （by 0.31 mg g-l）. Furthermore, the NM ＋ G treatment （perennial grazing） had the lowest density of Collembola （16.24 individuals m-2）, one of the two most common taxonomic groups, although other taxonomic groups responded differently to the treatments. Treatment effects on soil fauna were consistent with those on above-ground grasses, in which C：N ratios were greatly reduced by grazing, with this effect being the greatest for the NM ＋ G treatment. In contrast, different grazing treatments had little effect on C：N ratio of soil. Furthermore, the traditional grazing method （mowing followed by seasonal grazing） may have less severe effects on some taxonomic groups than perennial grazing. Therefore, an appropriate management should aim to protect soil fauna and microbes in this area from over-grazing and against further degradation.