Abstract: Aimed to study the dynamics of the biomass and its allocation of the rubber plantations with different stand age in Xishuangbanna of Southwest China, fifteen plots, each with a size of 25 m×40 m, were established at different sites. By using the investigation data of 30 rubber trees with different age and diameter at breast height, the regression model of the biomass relating with D (diameter at breast height, 13 m) and D²H was established, and applied to estimate the biomass of 15 rubber plantations with different stand age, and to analyze the allocation characteristics of the biomass with stand age. The total biomass of the stands increased with stand age, being 23.98 t·hm^-2 in 7yearod stand, 66.90 t·hm^-2 in 13yearold stand, 150.37 t·hm^-2 in 19yearold stand, 171.12 t·hm^-2 in 25yearold stand, and 25021 t·hm^-2 in 47yearold stand. The biomass of trunk occupied the greatest proportion, being 53.61% of the total in 7yearold stand, 57.79% in 13year old stand, .30% in 19yearold stand, 62.27% in 25yearold stand, and67.74% in 47yearold stand. Branch biomass also increased with stand age, from 15.14 % of the total in 7yearold stand to 18.20% in 47yearold stand, while root biomass decreased with stand age, being 25.54%, 20.22%, 16.93%,16.08%, and 12.47% of the total in the five stands, respectively. Leaf biomass contributed small, which also decreased from 3.11% of the total in 7yearold stand to 225% in 47yearold stand. Comparing with that of other forest types, the biomass of the rubber plantations in study area was far lower than that of the tropical seasonal rainforests and tropical monsoon rainforests over limestone, but higher than that of the secondary tropical forests in the same area and of the forest plantations in other tropical regions of China.

Key words: Cunninghamia lanceolata, Mixed forest, Soil quality assessment, Soil function