The Process and Mechanism of Degradation of Desert Riparian Vegetation
荒漠河岸植被的受损过程与受损机理分析

Based on the data of annual mean groundwater level,we divided the groundwater levels into six environmental gradients and data were sampled repeatedly six times from vegetation plots for each gradient of groundwater level.Through analysis of the changes in vegetation coverage,species diversity and structure of plant communities along the gradients of groundwater levels,the results were obtained to explain the degraded process of vegetation.Meanwhile,we analyzed the mechanism of vegetation degradation.The results showed that:(1) Degradation of richness of herbaceous plants happened at a depth greater than 4 m of groundwater level,while that of woody plants started at a depth of 8 m groundwater level.(2) The decrease of vegetation coverage was due to decline of herbaceous coverage.The threshold depth of groundwater level for coverage degradation was 4 m.This depth was the same as the depth of groundwater for degradation of species diversity.However,when the depth of groundwater was under 6 m,the decrease of vegetation coverage was due to decrease of coverage of woody plants.(3) Changes of two typical plant communities in vertical structure and species were characterized by the degraded succession of plant communities.In the process of degradation of Phragmites communis the dominant species was replaced,but the dominant species of the Populus euphratica community,namely Populus euphratica,retained its dominant position in the process of degradation.(4) The degradation of desert riparian ecosystem was resulted from interior vulnerability of the ecosystem and extrinsic human disturbance.The increase of population and requirements caused the increase in human disturbance,while the immediate reason of vegetation degradation was human overconsumption of the environmental resource-water,which was a dominant factor for vegetation survival.In the process of degradation of ecosystem,plant functional types and intensity of disturbance impacted the extent of vegetation degradation.