The Root Causes Of Desertification And Its Status Assessment In Semi-arid Agro-pastural Mosaic Area

Desertification is one of globally Environmental problems, about one third of the global territory is menaced by desertification. According to the latest statistics, the area of desertification in China is about 2622 thousand square kilometers, accounting for 27.3% of the whole territory. There are many controversies about the concept and distribution of desertification in the scientific field, but desertification combating had been carried out in all the affected countries for several decades, especially following the signature of UNCCD, the researches and practices on desertification and its control step into a new stage. Semi-arid agro-pastural mosaic area, as a fragile ecotone, is one of regions affected seriously by human activities. Due to its peculiarity in climate, soil, vegetation, landform, hydrology and so on, the significantly positive or negative feedback mechanism of desertification processes exists under human disturbance. In this paper, Yijinholo County, Inner Mongolia are selected out as a case study, on the basis of abundant data from local government, remote sensing image combined to field survey is applied. The study is aimed at the analyses of root causes of desertification and its status assessment, the theory and method of desertification and its control, to the extent, will be provided for the regionalized integrated development in the similar areas.The analyses to main meteorological factors by moving averaging (3 years and 5 years) show that, compared to mean values within 40 years, precipitation has no significant difference, while temperature and potential evapotranspiration have alternative high-low change, therefore humid index has an alternative dry-humid change which mans climate has no significant aridification tendency from 1960-1998. In addition, average drought frequency is 72.5 percent, there are also no significant difference, the fluctuation of meteorological factors in small temporal scale don't exceed the normal climate fluctuation, which indicates that a fragile climate background is provided for desertification processes. The seasonally alternative distribution of wind and rainfall provides energy for soil erosion and loose underlying material, erodible soil types and landform also provide the material basis for desertification.The analyses of social and economic development indicate that, up to 1998, the total population in Yijinholo County is 143,949 persons, the population density is 24 persons per square kilometer, large population number results in land exploitation for food and overgrazing in rangeland. The change in temporal and spatial pattern of landuse from 1977 to 1998 demonstrates that mobile sand dunes was replaced by rangeland and woodland andpartial shrubland in the middle of study area changed into rangeland and farmland from 1977 to 1987, while mobile sand dunes and rangeland transformed into shrubland and farmland in a small parts from 1987 to 1998, the above-mentioned change is proved by the change of fractal dimension index and fragmentation index at landscape and its element levels. The change of landuse patterns in 1977-1998 shows indirectly the desertified land had been restored and is being restored. The relationship between landuse patterns and soil types was also analysed in this paper, from 1977 to 1998, the areas of rangeland and mobile sand dunes decreased in most soil types and the areas of woodland, shrubland and farmland increased, which means that the modification of landuse patterns due to limitation of soil types will be helpful to desertification control. In a word, in a shorter temporal scale, irrational landuse patterns is the root cause of desertification, while rational landuse patterns is the effective way to restoration of desertified land. On the basis of temporal scale (century) and intensity classification (slight, moderate and severe), soil types vegetation cover and soil erosion intensities are determined as the assessment indicators, desertification status under different landuse types are assessed using the weighted addition equation, the assessment results indicate that in 3746.12 square kilometers of rangeland, the areas of slight, moderate and severe desertification are 29.53, 486.06 and 2316.55 square kilometers, accounting for 0.79%, 12.98% and 61.83% of total rangeland area respectively; in 336.14 square kilometers of woodland, the areas of slight, moderate and severe desertification are 78.97, 119.73 and 112.65 square kilometers, accounting for 23.50% 35.62% and 33.52% of total woodland area respectively; in 842.47 square kilometers of shrubland, the area of slight and moderate desertification are 359.76 and 140.51 square kilometers, accounting for 42.71% and 16.68 % of total shrubland area respectively, in 551.50 square kilometers of farmland, the areas of slight, moderate and severe desertification are 178.69, 51.64 and 174.39 square kilometers, accounting for 32.40 % , 9.36 % and 31.63 % respectively. Summing up the 4 above-mentioned desertification areas with the area of mobile sand dunes determined as severe desertification, the total desertification area in 5965.86 square kilometers of study area is 4255.5 square kilometers , accounting for 71.33% of the study area, among which the areas of slight, moderate and severe desertification are 787.55, 770.14 and 2697.81 square kilometers, accounting for 13.20%, 12.91% and 45.22% respectively, which indicates that desertification in Yijinholo County is still under dangerous status, further control activities is necessary.Limited by acquired data, this paper give a primary assessment to desertification status in Yijinholo County, the desertification rate and inherent risk should be assessed to better understand the desertification processes in this area.