Vegetation and vegetation dynamics in the Tarim River floodplain of continental-arid Xinjiang, NW China
Thevs, Niels; Zerbe, Stefan; Peper, Jan; Succow, Michael
Under the extreme continental-arid climate of Central Asia, vegetation is concentrated along the river systems, where groundwater is available throughout the year. This so-called Tugai vegetation provides an important habitat for plant and animal life and harbours the highest biodiversity in these regions. In our study, we focus on the Tarim River floodplain where the Tugai vegetation strongly declined since the 1950ies due to non-sustainable land-use and over-exploitation of water resources. We investigate the remnants of natural Tugai vegetation along the middle reaches of the Tarim River, where we still can find natural river dynamics. We follow the hypothesis that the groundwater depth and the salinization of the groundwater are the major factors, which influence the differentiation of the plant communities. The most frequent species in the 11 plant communities of the Tugai vegetation in the Tarim River floodplain are Populus euphratica, Tamarix ramosissima, and Phragmites australis. Most of the plant communities are located not more than 1 km away from the river courses or lakes and on sites with a groundwater level not deeper than 4 m. With increasing groundwater depth, the mean species numbers decreases. Recruitment of most of the species is limited to sites, which are flooded or inundated, respectively. Due to river course changes in the past decades, sites change from flooded to dry with groundwater levels deeper than 10 m and increasing soil salt content. Based on information on the spatial distribution of the plant communities and the river dynamics in the past decades, a succession scheme is worked out. During succession, which is driven by river dynamics, more and more species disappear according to their ability to grow deep roots in order to maintain groundwater contact and their ability to withstand increasing salt contents.