Characteristics of vegetation cover change in Xilin Gol League based on MODIS EVI data

Abstract: Xilin Gol League located in the middle of Inner Mongolia is not only one of the most important sand sources, but also the important protection barrier of ecological environment in North China. The condition of vegetation in the Xilin Gol League will affect the quality of ecological environment in Beijing-Tianjin-Tangshan (BTT) and even the eastern region in China directly. In this paper, the Xilin Gol League was selected as the research area, and the data set of fractional vegetation cover in Xilin Gol League during 2000-2013 was built based on MODIS EVI (enhanced vegetation index). The MODIS EVI data set during 2000-2013 was reconstructed by using the harmonic analysis of time series, because the product of MODIS EVI has noisy data under the effect of atmospheric conditions and land surface conditions. In order to extract the pure vegetation and pure bare land information for estimating the fractional vegetation cover effectively, the linear model was utilized in the decomposition of mixed pixels in the MODIS EVI data set. Then the fractional vegetation cover data set was estimated and built with the extracted information mentioned above based on MODIS EVI in Xilin Gol League. The temporal and spatial variation of vegetation in the study region was analyzed by spatiotemporal series analysis during 2000-2013. According to the study method and results, the average fractional vegetation cover showed a slight decline in Xilin Gol League and the annual maximum fractional vegetation cover increased with smaller amplitude on the whole. From the spatial distribution and variation, the fractional vegetation cover in eastern and southeastern area of Xilin Gol League was relatively high, such as East Ujimqin Banner, West Ujimqin Banner, Duolun County and Taibus Banner. However, the fractional vegetation cover of northwestern area including Sonid Left Banner and Sonid Right Banner was relatively low. From the temporal trend, with the influences of sandstorm, drought and other weather disasters, as well as the intensified husbandry activities in the study area, the overall improvement of fractional vegetation cover was not obvious, and the fractional vegetation coverage decreased significantly in part of the area, although the study area had carried out large-scale ecological environment protection measures, such as returning grain plots to forestry (grass) and afforestation for about 30 years, especially during 2000-2013. The phenomenon of grassland degradation and land desertification was becoming more and more serious. The fractional vegetation cover was gradually turning into the lower situation from the low status in the central area of Xilin Gol League, the fractional vegetation coverage between 0.4 and 0.6 decreased during 2000-2010, but was raised since 2013, and the area with high fractional vegetation cover gradually became higher in part of Xilin Gol League during 2000-2013. Through the study, the trend of spatial and temporal variation in Xilin Gol League was revealed clearly for the local region, and the cause of the phenomenon was also directly pointed out. Thus, the study content and result provide the reference for the protection and restoration of the local region, and even for the whole China. At the same time, the estimation method of fractional vegetation cover in the study can innovate the thinking and provide theoretical basis to some extent for arid and semi-arid region.