ECOLOGICAL EQUILIBRIUM AND PRODUCTIVITY OF MANGROVE FORESTS IN THAILAND

Abstract

Ecological equilibrium and productivity of mangrove forest were carried out at Hadsai Khao mangrove forest in Ranong Province by establishing the permanent study plots. Various characteristics of mangroves were investigated including forest structure, growth rate of mangrove trees, natural regeneration and growth of seedlings, biomass of forest above ground (stems, branches, leaves and proproots) and underground (roots), amount of nutrients especially nitrogen, phosphorus, potassium, calcium, magnesium and sodium produced by mangrove forest via litter fall. The results of this investigation can be summarized that the mangrove forest at Hadsai Khao in Ranong Province is composed of many vaieties of species and the common species are Sonneratia alba, Rhizophora apiculata, R. mucronata, Bruguiera cylindrica, B. parviflora, Ceriops sp. and Xylocarpus granatum. The occurrance of these species varied from the area at the bank of river to inland site as defined to species zonation. The study indicates that Sonneratia community occupies an area at the bank of river followed by the communities of Rhizophora, and Bruguiera-Ceriops. Xylocarpus community covers an area at the inland site. Stem density and basal area of each species zonation or each community were different form each others ranging from 500-8,900 trees/rai with basal area ranging from 19-200 m²/rai. The growth rates in diameters of mangrove tree species with diameter exceeding 4 cm varied from species to species with the values of about 0.1-0.7 cm/yr. Natural regeneration is quite abundant with the density of about 32,000 seedlings/rai. The height-growth of mangrove seedlings is about 30-54 cm/yr and diameter-growth above root-collar is between 0.6-1.8 cm/yr. The survival rates of mangrove seedlings are approximately 70-100%. The total above ground biomass including stems, branches, leaves and prop-roots of different species zonation is about 3-21 t dry wt./rai and the total underground biomass is high as 70 t dry wt./rai. The litter fall is about 1.4 t dry wt./yr with the litter decompose of 0.59 t dry wt./yr or about 41% of the total litter production. The total nutrient gained by mangrove forest via litter fall including nitrogen, phosphorus, potassium, calcium, magnesium and sodium is about 49.0 g/rai/yr.