Remotely Sensed Monitoring And Driving Forces Analysis Of Grassland Degradation In Maqu County

Maqu County, which is located in the eastern Qinghai-Tibet Plateau, is the most important area for conserving and recharging water for upper Yellow River, and is the major livestock production region in Gansu Province. Over the decades, due to natural factors-such as climate change and human factors-such as overgrazing, Maqu grassland had depredated with varying degrees. This not only directly impacted the sustainable development of livestock production in Maqu County, but also heavily impacted the ecological security of the upper and middle reaches of the Yellow River. Thus, accurate understanding the current situation and the reasons of Maqu grassland degradation has important scientific significance for the grassland degradation governance of this region.In this study, AVHRR NDVI and MODIS NDVI data from2000to2006was used to build the data converting model between these two data, and the AVHRR NDVI data from2007-2011was calculated by using this model; We developed the dimidiate pixel model for quantifying vegetation fraction from1984to2011in study area from AVHRR NDVI data, and the accuracy of this model was evaluated, then we analyzed the trend of vegetation fraction changing of Maqu from1984to2010by using linear regression method; We established the retrieving model of grassland biomass from AVHRR NDVI data, evaluated the accuracy of this model and calculated the grassland biomass of Maqu, then changing trend of Maqu grassland biomass was analyzed; Maqu grassland degradation situation from1984to2010was assessed by synthetic analysis of vegetation fraction and grassland biomass changing trend in this period; We analyzed the correlation between10chosen factors and grassland growth status respectively from1984to2010in study area, used the good correlation factors to further analyze the major driving factors that affect the degradation of Maqu and their contribution rate. The results show that:1) From1984to2010, the changing trend of vegetation fraction in the majority of Maqu grassland was declined. In the first period (during1984to1992), the condition of Maqu grassland vegetation fraction was well, changing trend in majority of grassland was recovery; In the second period-from1993to2001, the area of vegetation fraction declined region had increased and the vegetation fraction condition of Maqu deteriorated; During the third period (2002-2010), The deterioration level of Maqu vegetation fraction condition was heavier than that of the second period, because the decline area had increased sharply.2) During1984to2010, the fluctuation of Maqu grassland biomass was from decline to slight decline to significant decline. During the first period, the area of biomass declined region and heavy decreased region accounted for60.14%and92.12%of total grassland area, respectively; In the second period, the area of grassland biomass decline region had reduced, but the area of increasing and no-changing region had increased; However, during the third period, the biomass of72.97%grassland had decreased with a heavy decreasing level.3) During1984to2010, the area of grassland degradation region was increasing and the degradation degree was deepening. During the first period,43.24of grassland in Maqu had depredated, and the level of32.81%of degradation region was heavy; In the second period,50.00%of grassland in Maqu had depredated, and the level of62.16%of degradation region was heavy; During the third period,56.76%of grassland in Maqu had depredated, and the level of76.19%of degradation region was heavy.4) Five degradation driving factors have good correlation with grassland growth status from1984to2010in study area. They are annual stockbreeding population, annual total output value of agriculture, annual overgrazing rate, annual precipitation and annual mean temperature.5) The main driving force of Maqu grassland degradation during1984to2010was human activity, its contribution rate was64.28%, which is much higher than that of natural factor. In human factors, the first fact was total output value of agriculture with the contribution rate of64.28%, the contribution rate of stockbreeding population and overgrazing rate was relatively low. The first factor in natural factors was precipitation, the contribution rate of which was20.23%, and the second factor was temperature, which had9.76%contribution rate.