Abstract: By the methods of plot sampling and allometric dimension, this paper studied the biomass and its allocation in a 28-year-old Mytilaria laosensis plantation in southwest Guangxi. The biomass in the plantation was 281.47 t·hm^-2, and the biomass allocation was in the order of tree layer (97.89%) > litter layer (1.87%) > shrub layer (0.16%) > herb layer (0.08%). The biomass in the tree layer was 275.54 t·hm^-2, and the biomass allocation was in the sequence of stem (63.01%) > root (21.01%) > branch (9.64%) > bark (4.38%) > leaf (1.72%) > fruit (0.25%). The biomass of the trees with different diameter at breast height (DBH) was approximately in normal distribution, and that of the trees with 25-29 cm DBH accounted for 48.15% of the total. The mean annual net productivity of the plantation was 15.61 t·hm^-2·a^-1, and the net productivity of different components of the plantation was tree layer (81.50%) > litter layer (16.82%) > shrub layer (0.98%) > herb layer (0.70%). The mean annual net productivity of the tree layer was 12.72 t·hm^-2·a^-1, and the relative proportion of different tree organs was stem (48.76%) > leaf (18.64%) > root (16.26%) > branch (7.46%) > fruit (5.50%) > bark (3.39%).

Key words: Tamarix chinensis, fertile island, carbon, nitrogen, phosphorus, saline-alkali land.