The Study on Community Diversity of Both Castanopsis orthacantha and C delavayi Communities at Jizu Mountain,Yunnan

C orthacantha and C delavayi forests are the major types of semi humid evergreen broad leaved forests in the area of central Yunnan plateau.Their Community diversity is discussed in this paper. The results show that:①The species diversity index appears lower in C orthacantha community than in C delavayi community.The index is also lower in prime developing stage than in later stage or in transition zone.And the species diversity index drops when the layers go up in C delavayi community,but becomes higher in shrubs layer than herbs layer in C.orthacantha community.②The diversity of community consists of two parts.One is species diversity index,and the other is structure diversity index that can be measured by the increment of species diversity index when the distribution of species in layers has been considered.③With the community stability's rising,structure diversity index increase but species diversity index reduce.