关键词: 草地生态学, 草地退化, 草地生态系统

Abstract: Taking three types of residential areas in Beijing as the objects, this paper analyzed the tree species composition, relative important value, and three-dimensional configure in diameter at breast height (DBH), height, and crown coverage. In all types of the residential areas, there existed common key tree species, and also, unique dominant species. Populus tomentosa, Sophora japonica, and Platycladus orientalis were the common key species with higher important value; tall and straight species Paulewnia fortunei, Cedrus deodara, P. canadensis, and Ginkgo biloba were the important species in enterprise-institution residential areas; traditionally native species such as Ailanthus altissima, Fraxinus chinensis, and Ziziphus jujube were the essential components in Hutong residential areas; and excellent landscape tree species such as Robinia pseudoacacia, Pinus tabulaeformis, Salix babylonica,  and S. japonica cv. Pendula had valuable traits in mixed residential areas. As for the tree species three-dimensional configure, the overall distribution in DBH, height, and crown coverage in the three types of residential areas all presented a great development potential, being still at a rapid growth phase. With larger green space, enterprise-institution residential areas had significantly higher tree density, crown coverage, average DBH, and height than the other two types of residential areas; due to the limited green land, Hutong residential areas were difficult to increase the green biomass to a higher level; whereas mixed residential areas had considerable potential in the increase of green space.

Key words: Grassland ecology, Grassland degeneration, Grassland ecosystem