Abstract: The monsoon rain forest over limestone is one of the main tropical forest vegetation types in Xishuangbanna of Southwest China. To study the biomass and its allocation of this vegetation, three permanent plots (50 m × 50 m) were established at different sites. Grid method (10 m × 10 m) was used to record all the individuals with D≥ 2.0 cm in each plot, shrub and herb species were investigated in nine 5 m × 5 m and 2 m × 2 m subquadrates, respectively. The methods of allometric dimension analysis and sampling harvest were used to estimate the biomass of tree, shrub and herbage layers, respectively. Biomass regression equations of 5 dominant tree species, i.e., Cleistanthus sumatranus, Sumbaviopsis albicans, Lasiococca comberi, Cleidion brevipetiolatumand Celtis wightii, and of three Dclasses (2-5, 5-20 and >20 cm) for the forest stands were established. The results showed the total biomass of monsoon rain forest over limestone in Xishuangbanna was （319.158±79.740） t·hm^-2. Living biomass made up 96.32% of the total biomass, and coarse woody debris and litterfall hold the rest. Tree, woody vine, shrub and herbage layers occupied 96.80%, 2.68%, 0.39% and 0.12% of the living biomass, respectively. In the allocation of tree biomass to various organs, stem accounted for 63.72%, and root, branch and leaf made up 18.82%, 15.63% and 1.84%, respectively. Among different Dclasses of tree layer, the biomass allocation concentrated on the medium (20≤D≤40 cm) and the largest classes (D＞40 cm). A few dominant species, in terms of biomass, made up a majority of the total biomass of tree layer, and the mean leaf area index (LAI) of the tree layer was 7.697±1.419. Compared with other tropical forest types, the estimated biomass of the monsoon rain forest lied in the lower range of the published values for tropical moist rain forest, and was lower than that of tropical seasonal rain forest in Xishuangbanna but higher than that in Puerto Rico and Rio Grande karst forests.

Key words: Atrazine, Soil fertility, Soil urease