Abstract:

The upper reaches of Bailong River, a significant branch of the Yangtze River, is one of the important regions in the Yangtze River Natural Forest Protection Project. Based on the survey and the data from 36 plots, characteristics of species diversity of plant communities in the upper reaches of Bailong River were discussed in this paper. The study showed that richness index varied as follows: tree layershrub layer>tree layer; b) moss-A. fargesii community: tree layer > shrub layer> herb layer; and c) other communities: shrub layer > herb layer> tree layer. Diversity indices in tree layer were lower than that in herb layer and in shrub layer. While the diversity indices between herb layer and shrub layer varied with shade density, i.e. greater the shade density, lower the diversity indices in herb layer. When shade density of stand was about 45%, diversity index in herb layer were almost equal to that in shrub layer; when shade density of stand was about 30%, diversity index in shrub layer were lower than that in herb layer; when shade density of stand was above 55%, diversity indices in shrub layer were higher than that in herb layer. General richness index, evenness indices and species diversity of Pinus tabulaeformis community distributed on the sunny slope were higher than that of the grass-Picea asperata community growing on the shady slope along the same elevation zone (2 500-2 700 m). The study detected that general species diversity and general evenness indices of different plant communities decreased gradually from broadleaf mixed community dominated by Quercus liaotungensis at 2 400 m elevation, to grasses-Picea asperata community at 2 600 m elevation, to bamboo　(Sinarundinaria nitida)-A. fargesii community at 2 800 m elevation, to moss-A. fargesii community at 3 000 m elevation, to R. fastigiatum - A. fargesii community at 3 200 m elevation zone, and then progressively increased in R. fastigiatum shrubs from 3 400 m, with altitudinal increase. The study also indicated that species diversity and evenness index gradually increased from shrubs stage dominated by Spiraea alpina and Sibiraea angustata to broadleaf mixed forest stage dominated by Betula albo-sinensis, to broadleaf and needleleaf mixed forest stage dom inated by B. albo-sinensis and Picea purpurea, and then decreased at the needleleaf community stage dominated by P. purpurea in the natural succession series of P. purpurea community after artificial logging.