Dynamic And Driving Forces Of Grassland Vegetation Patterns In The Xilin River Basin For Nearly Three Decades

Grassland is the largest terrestrial ecosystem of China. An the important land resources, it plays a crucial role in ecological, economic and social values. Since the last three decades, althouth the economic showed rapid development, grassland ecosystem degraded seriously. Meanwhile, vegetation pattern has also changed a lot. Grassland degradation intensity affected ecosystem stability, reduced ecosystem function, and then may hinder social-economic development.The study about vegetation patterns and dynamics is an important approach to comprehensive and deeply understand the phenomenon of ecosystem degradation, and explore its inherent mechanism. This research was conducted in Xilin River Basin. Based on satellite remote sensing data of medium resolution:Kate-2003of Russia and landsat TM image data, the vegetation patterns and dynamics were analysed from1983to2011using softwares of ArcGIS and eCognition. The main objective was to reveal the time-space vegetation pattern change and its driving force. It will help furthermore to get a comprehensive understanding about the problem of grassland degradation. There were five important findings:1) Based on ArcGIS software and digital elevation model (DEM), it is efficient to define accurate and objective natural basin boundary;2) Grassland is the dominant vegetation type, and distributes with obvious regularity:meadow steppe and typical steppe appeared in turn from southeast to northwest. In addition, intrazonal vegetation, such as sand and wetland meadow distribute patchy;3)In the recent30years, the area of natural grassland reduced continuously in Xilin River Basin. It reduced about7.36%. Especially, areas of medium forbs meadow steppe, Leymus chinensis and Stipa grandis grassland declined by42.5%,30.7%and47.4%respectively, In contrast, the area of shrubbed grassla increased significantly. For example, the area of Caragana microphylia shrubbed grassland increased by1.24times. Meanwhile, both desertification and saline land expanded significantly, the former increased by53.67%, the growth rate of the latter maintained at about8%.4) Based on landscape index, vegetation patten changed obviously. At the landscape scale, PD, LSI and SHEI is increased, LPI and CONTAG is reduced, degree of fragmentation became more intensity. At the class scale, the PD of medium forbs meadow steppe and Leymus chinensis grassland increased and the LSI bicame more complex. The two grasslands became more fragmentation.5) The main drivers of grassland degradation and vegetation pattern changes was land use change, livestock production and socioeconomic. The land policy of "two rights and one system" played an active role for the restoration of the degraded grassland. Moreover, natural factors, mainly precipitation, is also very important for the pattern change rather than fragmentation. Biological factors also can influence vegetation pattern.This study should be helpful to improve the local ecological environment protection and construction with the clear understand of vegetation pattern change and its drivers in Xilin River Basin. At the same time, they were significant meaningful for sustainable development of nature, social and economy in arid and semiarid region of china.