Analysis of Dynamics and Driving Factors of Wetland Landscape in Zoige, Eastern Qinghai-Tibetan Plateau

摘要

Zoige Wetland is one of the largest plateau wetlands in the world. This paper provides a dynamic analysis of spatial and temporal patterns of the wetland in Zoige, Eastern Qinghai-Tibetan Plateau, supported by ERDAS8.7 and ArcGIS9.0. It is the first comparative analysis of a system of rapidly changing wetland with landscape patterns in Zoige, using 3 classified landsat Thematic Mapper images of 1977, 1994 and 2001. The classified images were used to generate wetland distributing maps, and shape index (S), diversity index (H), dominance index (D), evenness index (E), fragmentation index (F) and fractal dimension (F<,d>) were calculated and analyzed spatiotemporally across pure grazing area in Zoige for each landscape type and in different periods (before 1977, during 1977～1994 and 1994～2001), as well as the driving forces of natural and anthropogenic. The study shows that for a comprehensive understanding of the shapes and trajectories of the shrinking and desertificated land expansion of the wetland, a spatiotemporal landscape metrics analysis in different periods is an improvement than only with landscape changing rates. This type of analysis can also be used to infer underlying social, economic, and political processes that drive the observed wetland forms. The results indicate that wetland patterns can be changed over relatively short periods of time. The total area of lake reduced by 164.86 km2, grassland extended by 141.74 km2, semi-marsh extended by 105.94 km2, marsh reduced by 86.00 km2: the number of landscape patches reduced by 56, and their average area decreased by 2.68 km2: the successions within lake, marsh, semi-marsh and grassland were found obviously; S decreased stepwise; D and F increased but H decreased: The changing rate after 1994 was 2.3 to 2.9 times greater than that before. The change of the wetland landscape patterns resulted in the interaction between socio-economic and natural forces of positive and negative aspects; and natural factors affected as assistant aspect. Some important human activities in this period led to the change of the landscape patterns in this region directly. Some measurements made by government and NGO delayed the converting process partly.