Analysis on the Coenological Characteristics of Monsoonal Evergreen Broad-leaved Forest Communities in Xishuangbanna

The species and floral composition,forest structure,plant diversity and coenological characteristics of the monsoonal evergreen broad-leaved forest(MEBF) in xishuangbanna are studied.The results showed that total number of plant species in the communities of MEBF is 70～123,representing 70～74 genera and 36～49 families in three 2 500 m~(2)plots.The floral composition of those communities can be divided into 12 floral types.Among those floral types,Pan-tropic and Trop.Asia(Indo-Malesia)distributions are dominant,but temperate distributions are only a little.Tree species richness(DBH≥2 cm)is 60± 11.14,while Shannon-Wiener and Pielou'sevenness indicesare 2.605 1± 0.342 0 and 0.637 3± 0.065 4,respectively.The structure of communities is complex which can be divided into tree layer(I,II),shrub layer and herb layer.The forest is characterized by evergreen mesophanerophytes and microphanerophytes with simple leathery and entire mesophyllous leaves,a relatively low abundance of woody lianas,few buttressed trees and little or no caulifory.It is also revealed that the species-area curve for the forest type increased very slowly after 1 500 m~(2)sample area.Compared to the seasonal rain forests and the montane rain forests in Xishuanbanna,the MEBF has a higher meso-and micro-phanerophytes,but a lower megaphanerophytes,more plants with simple,leathery and mesophyllous leaves.Compared with the evergreen broad-leaved forest in other regions,mesophanerophytes,entire leaves and mesophyllous leaves are more abundant in the MEBF of Xishuangbanna,but has fewer plants with microphanerophytes and microphyllous leaves.The MEBF in Xishuangbanna has lower species diversity than that in the seasonal rain forest and in the montane rain forest of the same region,and that in the evergreen broad-leaved forest in Guangdong,but similar to evergreen broad-leaved forest in Ailaoshan mountain inYunnan and Tiantaishan mountain in Zhejiang.however,species diversity of MEBF in Xishuangbanna was higher than that of the evergreen broad-leaved forest in the middle region of Yunnan,Chongqing and Okinawa island of Japan.This indicates that the mosoonal evergreen broad-leaved forest in Xishuangbanna has obvious transitional characteristics from rain forest to the evergreen broad-leaved forest in the middle subtropical China.