Coenological Characteristics of Tropical Montane Rain Forest in Xishuangbanna

Tropical montane rain forest (TMRF),one of the primary forest vegetation types in Xishuangbanna,occurs at lower altitude in the north (TMRFⅠ) and higher altitude in the south (TMRFⅡ).In order to understand the community characteristics of tropical montane rain forest in different zones,four permanent plots (50 m×50 m) of tropical montane rain forest communities at different sites in Xishuangbanna were established,two of which were for TMRF I and two for TMRF II.The grid method (10 m×10 m) was used to record all individuals with DBH greater than 2.0 cm in each plot.Shrub and herb species were investigated in nine 5 m×5 m and 2 m×(2 m) sub-quadrates respectively.Plant species composition,physiognomic characteristics of those communities were analyzed.The results showed that,in the 2500 m² plot,total number of plant species in the communities of TMRF is 105-178,representing 80-130 genera and 46-61 families.The floral composition of those communities can be divided into 11 areal types and the tropical distribution composition accounts for about 90%.Among those floral areal types,Pantropic and Trop.Asia (Indo-Malesia) distributions are dominant,accounting for 23.4%-32.88% and 25.2%-36.67%,respectively.Concerning about the life form spectrum,phaenerophytes are (dominant) in the communities,among which the proportion of meso and micro-phaenerophytes are very high,accounting for about 50% and 21.30%-27.78%,respectively.Concerning about the leaf characteristics,the communities was composed mainly of leaves whose characteristics are mesophylls (72.66%-82.54%),single (75%-86.33%),papery (58.73%-62.22%),entire (76.67%-83.33%) and no-caud.(about 90%).Compared with the communities of TMRFⅡ,the communities of TMRFⅠhas more tropical distributional plants,more lianas,mesophylls and entire leaves,but has less micro-phaenerophytes.This indicates that the communities of TMRFⅠare more close to the typical seasonal rain forest in Xishuangbanna.Compared with the communities of ravine and lower hill seasonal rain forests in Xishuanbanna,the communities of TMRF have less tropical distributional plants,mega-phaenerophytes and lianas,as well as less mega and macrophylls,but have more temperate distributional plants,micro-phaenerophytes and microphylls.This indicates that the communities of TMRF have obvious transitional characteristics from seasonal rain forest to evergreen broad-leaved forest.