Abstract: Through investigating the forest vegetation of the Dongling Mountain, Beijing, which is a region in warm temperate climate zone of China, the authors have caculated three diversity indices in the 20 plots belonging to several different plant communities, respectivey, and found that there are variations among different communities and the zonal vegetation community type has the highest diversity. This situation is also true in northern subtropical and southern subtropical zone. From warm temperate, northern subtropical, to southern subtropical zone, there is an evident tendency of gradual increase in species diversity. This is mainly because of the more solar energy, higher temperature, more precipitation and higher nutrient cycling rate in the lower latitudinal zone, though several other hypotheses proposed earlier may be partially applicable to our findings, from the point of view of community succession, the plant communities in a later stage of a succession series have higher diversity. The plant community tends to be more stable as the community diversity increases, at least to some extent, though thereare still many theoretical controversies on whether complexity and diversity will increase the ecosystem stability.

Key words: Dongling Mountain, Forest vegetation, Species diversity