Tree growth, dynamics, and productivity in a mature mangrove forest in Malaysia

Abstract

Growth of selected Rhizophora apiculata (Rhizophoraceae) trees was monitored from 1920 through 1981 in a 0.16 ha plot of protected forest in the Matang Mangroves. Starting in 1950, the sample was increased to include monitoring the growth of all the trees more than 10 cm dbh (diameter at 1.3 m or above prop roots). All seedlings were censused by species and removed in 1920 and recensused in 1926, 1927, and 1981. Total above-ground dry weight (biomass) of the forest was estimated using stand tables and a regression equation of biomass on dbh calculated for destructively sampled R. apiculata trees from elsewhere in the Matang Mangroves. Net primary productivity (1950–1981) was calculated from estimated biomass increments and published litter-fall rates. Rhizophora apiculata has maintained its dominance of the plot since 1920 but Bruguiera gymnorrhiza (Rhizophoraceae) and several other more shade-tolerant species have steadily increased in abundance. Between the 1920's and 1981, R. apiculata declined in relative abundance in the seedling layer while B. parviflora and B. cylindrica increased. Mean mortality rate (1950–1981) for trees more than 10 cm dbh was 3.0% per year with a range of 1.3–5.4% per year. When trees fell over and hit other trees, the damaged trees usually died within 10 years. A major cause of mortality appeared to be sapwood-eating termites. Net primary productivity averaged 17.7 t/ha/year over the 1950–1981 observation period. Biomass ranged from 270 to 460 t/ha with a mean of 409 t/ha. It is suggested that Rhizophora spp. trees greater than 50 cm dbh and mangrove forests with total above-ground biomass exceeding 300 t/ha would develop in other areas outside of the region affected by hurricanes if the forest was protected from human disturbance.