SPECIES DIVERSITY DYNAMICS OF FRAGMENTED TROPICAL RAINFORESTS IN THE LOWER-LANCANG/UPPER-MEKONG RIVER BASIN

Abstract

Three fragments of tropical rainforest in Xishuangbanna, southern Yunnan and within the Lower-Lancang/Upper-Mekong River basin, were sampled to investigate species diversity patterns based on comparisons with a contiguous tropical rainforest. Compared with the contiguous forest, the fragments were lower in plant abundance, species diversity indicies, a lower percentage of mega-phaenerophytes, meso-phaerierophytes, chamaephytes and epiphytes, but had a higher percentage of liana, micro-phaenerophytes and miniphacncrophytcs. Thc floristic composition was also different in the fragments with a greater percentage of pan- tropical and tropical Asia to tropical Africa elements increased, whereas the percentage of regional or local elements decreased. Meanwhile, tree species in the upper canopy layer were more stable than that in the lower layers of the fragmented forest. The animal species diversity and evenness were higher in the contiguous forest than in the fragmented forests, which apparently were due to better habitat size and quality. The relationship between changes in the microclimate of the forest fragments and species changes were also considered. The interior forest of the fragmented forests transformed from a wet-cool to dry-warm microclimate, called the internal effect, and was found to be an important mechanisms accounted for observed species changes.