荒漠河岸植被的受损过程与受损机理分析

以塔里木河多年平均地下水位数据为依据,将地下水位划分为6个环境梯度,各梯度上6次重复采集植被样地数据.从物种多样性、植被盖度与群落类型等几方面分析了植被的受损过程,以及导致此过程的受损机理.结果表明：（1）草本植物丰富度受损发生在地下水埋深大于4 m,而木本植物丰富度受损发生在地下水埋深大于8 m.（2）植被盖度减少始于草本植物盖度受损,与群落多样性受损的临界地下水位相同,发生在地下水埋深大于4 m;在地下水埋深大于6 m之后,植被盖度不断减少则是由木本植物盖度的减少所引起.（3）群落类型受损体现在芦苇群落和胡杨林群落的结构与类型变化上,芦苇群落的衰退演变出现了优势种的更替,而胡杨林群落中优势种的优势地位没有变化.（4）此受损过程是由荒漠河岸生态系统脆弱的生态基质和外界干扰共同作用的结果,起因于人口的增加、需求的增长.植被退化是人类干扰作用于植被赖以生存的环境主导因子所致.在生态受损过程中,植物功能型差异与所承受的干扰强度差异对植被退化的程度有一定影响.

The Process and Mechanism of Degradation of Desert Riparian Vegetation

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.