Dynamics of tree species composition and community structure of a tropical seasonal rain forest in Xishuangbanna,Southwest China

We studied the dynamics of tree species composition and community structure in an 1 hm2 tropical seasonal rain forest plot in Xishuangbanna between two censuses in 1993 and 2007.All the trees DBH(diameter at breast height) ≥ 5 cm in the plot were measured and identified in 1993 and 2007 respectively.The results of 2007 survey showed that the proportions of tropical affinity at the levels of family and genus were 91% and 94% respectively,which was generally consistent with the pattern of the first census conducted 14 years ago.The number of tree species in the plot increased from 145 in 1993 to 179 in 2007,and the proportion of tree species with only one or two individuals decreased from 54% in 1993 to 5 1.1% in 2007.The mortalities of trees in layers A,B and C were 12.8%,12.9% and 19.0%.Correspondingly,the rate of tree recruitment were-8.5%,-1.4% and 44.8% in layers A,B and C.Meanwhile the proportion of stems with small DBH classes increased significantly.However,the number of trees and the number of species in layers A and B kept relatively stable.Over the last 14 years,the pioneer tree species in layers A and B in 1993 were excluded,even though some other pioneer tree species(fewer than five) were recruited into the layer C in 2007.In conclusion,the species composition and structure of this forest were changed in terms of treefall and recruitment during the past 14 years,but the general vegetation pattern of the the forest was kept in a state of dynamic equilibrium.