Abstract: The total above-ground biomass was 38.527, 20.012 and 29.405t·hm^-2,respectively in Sonneratia carseolaris(6-year-old)-Kandelia candel(11-year-old) mixed plantation(type Ⅰ), S. carseolaris pure plantation(type Ⅱ) and K.candel pure plantation (type Ⅲ). In type Ⅰ, the biomass of tree layer accounted for 41.0%, shrub layer for 59.0%; in type Ⅱ, tree layer for 93.3%, shrub layer for 6.7%; and type Ⅲ, 100% for shrub layer. The annual mean net accumulation of dry matters was 4.701,3.380 and 2.673t·hm^-2, respectively for these three types. The total accumulation of 10 elements in three plantations was 765.570,343.935 and 555.886kg·hm^-2 respectively, signifcantly different with different stand types; among them, 41.8% distributed in the tree layer and 58.2% in the shrub layer for type Ⅰ, 92.3% in the tree layer and 7.7% in the shrub layer for type Ⅱ, and 100% in the shrub layer for type Ⅲ. The amount of nutrient elements absorbed for an unit net accumulated dry matter production and their return rate varied with stand types. In types Ⅰ,Ⅱ and Ⅲ, the total amount of 10 elements absorbed for producing a ton net accumulated dry matter was 39.860, 36.834 and 18.904kg respectively; and their return rate was 61.3%, 40.4% and 72.2%, respectively.

Key words: Mangrove forest, Sonneratia carseolaris-Kandelia candel mixed plantation, Pure plantation, Biomass, Nutrient elements, urbanization, ecological stress, landscape pattern, ecological protection, regional ecological security