荒漠河岸植被的受损过程与受损程度的判定

以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、植被盖度等几方面分析了不同地下水位梯度上植被的受损过程,以及不同河段的受损程度.结果表明：（1）草本植物丰富度受损发生在地下水埋深大于4m,而木本植物丰富度受损发生在地下水埋深大于8m;（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4m;在地下水埋深大于6m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）生态受损程度可归为三类：潜在沙漠化类（轻度退化）,轻度沙漠化类（中度退化）,中度或重度沙漠化类（重度退化）.三种退化类型的地下水埋深依次增大,物种多样性与植被盖度依次减小,沙漠化指数也依次增强.

The Degred Pross of Desert Riparian Ecosystem and It s Degree of Degradation

Based on the data of mean annual groundwater level,we divided six gradients of groundwater levels and sampled six vegetation plots in every gradient of groundwater level. Through analyzing the changes in vegetation coverage, species diversity and structure of plant communities along the gradients of groundwater levels,we got the results to explain the degraded process of vegetation,at the same time,we analyzed the mechanism of vegetation degradation. The results showed. （1） Degradation of rich- ness of herbaceous plants happened at the 4 m groundwater level,while that of woody plants started at 8m depth of groundwater level. （2） The decrease of vegetation coverage was due to decline of herbaceous coverage. The threshold depth of ground water level for coverage degradation was 4 m. This depth was same with depth of groundwater for degradation of species diversity. However, depth of ground water was under 6 re,the decrease of vegetation coverage was due to decrease of coverage of woody plants. （3） The degraded ecosystem at the study area could be divided into three types by duster analysis namely the light degradation,the serious degradation and intergrade degradation. The slight degradation of ecosys- tem appears in the upper section of the lower reaches,with the relative shallow groundwater and high index of biodiversity and dense vegetation coverage. While the serious degradation of ecosystem can be found in the area near Taitema Nor. where the groundwater level is deeper more than 10 m,little species can survive.