围封年限对藏北退化高寒草原植物群落特征和生物量的影响

Effect of Enclosure Ages on Community Characters and Biomass of the Degraded Alpine Steppe at the Northern Tibet

为了评估西藏生态安全屏障工程-围封禁牧工程对高寒退化草地植被恢复效益,本研究在申扎高寒草原与湿地生态系统观测试验站附近,采用样线法和样方法对围封8年、围封4年和自由放牧的藏北高寒草原群落特征和生物量进行调查与采样分析。结果表明:自由放牧样地经过围封后,群落结构由杂类草矮火绒草(Leontopodium nanum)和昆仑蒿(Artemisia nanschanica)转变为多年生禾草紫花针茅(Stipapurpurea)和青藏苔草(Carex moorcrofii)为优势种的植物群落,植被高度、盖度、丰富度和多样性均增加。但是,围封后地上生物量却呈降低趋势。因此,应结合各个指标与群落结构特征综合评价退化草地的恢复状况。

In order to estimate the effect of the ecological engineer-forbidding grazing,we selected three plots（enclosed 8years,enclosed 4years and free grazing）to investigate the characters and biomass of the degraded alpine steppe using line transect and quadrat sampling method at the Xainza alpine steppe and wetland ecosystem observation station.The results showed that the dominance species of community structure changed from Leontopodium nanum ＋ Artemisia nanschanica to Stipa purpurea ＋ Carex moorcrofii.The species richness and biodiversity of community and the height and the coverage of community enhanced.However,the above ground biomass decreased after 8-year enclosure because of the change of dominant species.The biomass of forb（L.nanumand A.nanschanica）was greater in the free grazing plot because it was inedible by livestock.On the contrary,forb biomasses decreased and the grass biomass increased in the enclosed plots,and resulted in the decrease of total biomass.Therefore,for estimating the effect of the ecological engineer,we should think whether or not the estimated indexes consisted of community character,which could help us estimate the effect of ecological engineer accurately.