民勤荒漠区植被退化动态定位研究

白刺、沙蒿、麻黄是民勤荒漠区的主要植物种类,梭梭是当地主要固沙造林树种。定位监测表明:民勤5月下旬土壤含水率与灌木、草本植物和优势种密度及植被总盖度之间呈正相关关系。6~7月的降水量与灌木密度和植被总盖度之间呈正相关关系。5~7月的降水量和土壤水分是限制当地荒漠植被密度、盖度的关键因子。从群落类型看,深根性的麻黄和梭梭盖度比较稳定。从地貌看,流动沙丘和半固定沙丘上的植被较稳定,固定沙丘植被普遍严重退化。设置黏土沙障易形成沙面结皮,阻止降水下渗,不利于接收和保存有限的天然降水。

Study on the Dynamic Vegetation Degeneration in the Minqin Desert Area

Nitraria tangutorum,Artemisia arenaria and Ephedra przewalskii are the main species of natural vegetation in the Minqin desert area,especially Haloxylon ammodendron is a key sand-fixation species in this area.In this study,a positioned investigation on the dynamic vegetation degeneration in Minqin was carried out during the period of 2002-2006.The results reveal that the desert vegetation is continuously degenerated,and the vegetation coverage is closely related to precipitation.There is a significant positive correlation between the soil moisture content and the shrubbery density,herbaceous and dominant species vegetation as well as the total vegetation coverage in late-May.Rainfall during the period from May and July is a key factor affecting the desert vegetation coverage and the plant density in the study area.Viewing from the aspect of plant communities,the coverage of Ephedra przewalskii with deep roots and of Haloxylon ammodendron with high plants is comparatively stable.Viewing from the aspect of landforms,the vegetation on mobile and semi-fixed sand dunes is comparatively stable,whereas the vegetation on the fixed sand dunes is seriously degenerated.It is easy to form sand-surface crust and prevent rainwater to infiltrate downward if sand barriers are constructed,such construction,however,is disadvantageous for receiving the limited rainfall,so it is not an ideal measure to construct the clay sand-barriers for fixing sand.