额济纳绿洲沙漠化对柽柳群落影响的研究

柽柳群落是黑河下游额济纳绿洲重要的荒漠河岸林，有河滩和沙地两个亚群系。通过对该区域的考察和对植物群落、土壤的取样分析，表明了在绿洲因水资源短缺而发生环境恶化的过程中，两个亚群系均产生了群落衰退，包括群落种类组成趋向柽柳单一种群，当年生物量占现存生物量比率下降，枝条枯死率上升，而群落盖度、植丛高度、丛幅等无显著变化，因此评估沙漠化的指标应以枝条枯死率为主。土壤表层盐分、有机质和机械组成在河滩系列变化较缓，沙地系列较强烈。在水资源持续短缺情况下，柽柳群落演替的最终结果是柽柳全部死亡后直接演变成裸地和流沙。柽柳群落是额济纳绿洲面积最大的群落类型，因而也是阻止、延缓绿洲沙漠化的最后防线，应注意保护和抚育。

Influence of Sandy Desertification on Tamarix Community in Ejin Oasis

Tamarix community is an important vegetation type distributing on flood land and sandy land in Ejin oasis at the lower reaches of Heihe River. The vegetation and soil were sampled and the two sub-formations of Tamarix community were found at the flood land and sandy land. The characteristics of Tamarix community structure and the soil elements showed that the vegetation is going in the different degraded stages of desertification process. The specie richness and the biomass decreased, the rate of dead branches increased, but no significant change in the coverage, plant high, and plant cluster size. The change of soil element was not much clear with the degradation degree of the sub-formation at flood land, but at the sandy land sub-formation, the salt content of topsoil layer increased, the nutrient, and the organic matter, N and fine particles that less than 0\^1 mm significantly decreased. The Tamarix community is the last line to prevent desertification development in the area; we should pay more attention to it and protect the community.