Study on the Species Abundance Distribution of Tropical Dipterocarp Rain Forests in Xishuangbanna

Species-abundance relationship,one of the most fundamental characters of community structure,is a very important issue in community ecology.Based on the tree(with DBH greater than 1cm)data collected from the 20-ha plot of tropical rainforests of Xishuangbannan,species abundance distribution pattern is analyzed in this paper.The results showed that.(1) Thirteen of 468 species(2.78%)had more than 1 000 individual ≥1 cm DBH,which represented 56.36% individuals of the total.On the other hand,230 of 468 species(49.14%)had a mean density ≤1 tree per ha in the 20-ha plot.(2) There was a significant difference between the observed species-area relationship and the random placement model,which indicated that species did not have a random distribution in the plot.Also the species-abundance distribution of the plot could not be well fitted by using the lognormal model confirmed this.(3) The log serial model could not fit the species-abundance well(but better than the lognormal model),which indicated that the environment was not the determining factor,but it indeed contributed much to the species abundance distribution.