Abstract: The biomass dynamics of the pioneer Trema orientalis community in the early stages of secondary succession of tropical forest in Xishuangbanna had been studied for 5 years by the standard tree regression(for trees)and clear cut method(for shrub,herb and inter layer plants). 1)The biomass distribution by organs was ranked as stems>branches>roots>leaves. 2)As the succession proceed, the percentages of stem and root biomass increased gradually, the percentage of leaves obviously decreased, and the percentage of branches fluctuated slightly; the dorminant species T. orientalis was replaced gradually by other species,that made the biomass distribution by species appeared to have a characteristics of relative dispersion;the biomass distribution by DBH class showed that biomass was mainly determined by the amounts of larger DBH class trees;the percentage of the tree biomass to the total community biomass gradually increased, the percentages of the shrub and herb layers remarkably decreased and the percentage of the inter-layer plants increased slightly.

Key words: spring maize, coupling effect of water and nitrogen, saving water irrigation, Wuwei Oasis of Shiyang River Basin.