黄土沟壑区植被恢复过程中植物群落组成及结构变化

Changes in composition and structure of plant communities during the course of restoration at loess gully region

在 1 98 1、1 988和 2 0 0 1年 3个时期调查数据的基础上 ,对纸坊沟流域恢复生态系统中的植物群落的组成和结构进行了对比研究。结果表明 :对于中度退化生态系统 ,短期封禁就能使草本群落得到明显恢复。主要表现在植物种类的增加、植被盖度的提高和生物量的提高 ,其增加幅度分别为 7%～ 73%、81 %～ 1 67%和 61 %～ 1 38%。伴随着植被恢复 ,植被保持水土功能增强。流域土壤侵蚀从封禁前的极强度侵蚀 ( 1 0 0 0 0～1 40 0 0 t/( km2·a) )减小到轻度侵蚀 ( 1 2 1 0 .2 t/( km2·a) )。中期封禁过程中群落盖度、生物量继续增加 ,水土保持功能进一步提高 ,但和短期封禁恢复相比 ,提高幅度较小 ,群落盖度和生物量分别增加了 3%～1 8%、- 4%～ 8%。随着植被水土保持功能的加强 ,土壤表层养分也逐渐提高。中期封禁后群落结构和短期封禁相比发生较大变化 ,其中天然草本群落中发生了优势种更替现象 ,但天然灌木群落和人工乔灌群落优势种变化不大或无变化 ;群落垂直结构变化表现为 :草本群落结构变化最大 ,人工乔木林次之 ,但灌丛结构变化相对较小。封禁消除了致使植被退化的影响因子后 ,促进了群落内物种的正常生长和繁殖 ,从而使群落生态功能得到恢复 ;群落生态功能的恢复使群落生境得到改善 。

The changes occurred in composition and structure of plant communities in Zhifanggou watershed at Loess Gully region of China, constitutes major objective for the present study. The ground data was collected through field surveys during 1981, 1988 and 2001 respectively to analyze the significant relationships existing between plant composition, structure and their changes. Based on statistical analysis, the following conclusions could be made such as considerable increase in number of species (7%～73%), coverage (81%～167%) and above ground biomass (7%～73%), decrease in soil erosion modulus of Zhifangguo watershed from 14000 to 1210.2 t/(km^2·a) and, possible restoration of moderately degraded plant community by preventing the cattle's grazing at least for shorter periods (7 years) etc. The other findings includes a rise in both coverage (3%～18%) and above ground biomass ((-4%～8%)) of plant communities in middle of the period owing to the restoration as well as prevention of cattle grazing. It also facilitated the rise of soil nutrients as well. During the same middle period, there also observed remarkable changes in the plant community structure. In the case of natural grass communities, the dominant species were replaced by others through the process of succession. However, there were no domain subrogation species in shrub and forest communities. The changes in vertical structure of grass communities is most significant than of the forest communities. However, the vertical structure of forest communities stands a little higher than shrub communities. Moreover, the prevention of grazing benefits both plant growth as well as propagation which guarantee further restoration ultimately improving the quality of that habitat. The communities will be developed in the direction of climatogenic succession through the interaction of both plants and their habitat qualities. Finally, the formula proved in this paper also useful to measure remarkable changes in the community structure.