Net primary productivity of two mangrove forest stands on the northwestern coast of Sri Lanka

Abstract

Productivity studies were carried out from September, 1985 to August, 1987 in two mangrove stands, i.e. estuarine and island fringing, in Dutch bay, a lagoon situated on the northwestern coast of Sri Lanka. Net above-ground primary productivity was measured by monitoring litterfall and above-ground biomass increment. The average annual rate of litterfall in the estuarine and island-fringing mangrove stands are 588.14 g m−2 (approximately 6 t ha−1) and 407.33 g m−2 (approximately 4 t ha−1) respectively. The average annual rates of above ground woody growth are 614.74 g m−2 (approximately 6 t ha−1) in the estuarine stands and 286.8 g m−2 (approximately 3 t ha−1) in the island-fringing mangrove stands. Hence estuarine mangrove stands record a higher annual rate of above-ground net primary production (NPP; 1207.88 g m−2 or approximately 12 t ha−1) than the fringing mangrove stands (694.22 g m−2); approximately 7 t ha−1). The annual rate of NPP in the water front zones of the stands (1300.47 g m−2 in the estuarine stands and 874.56 g m−2 in the fringing stands) are greater than those in the back-mangrove zones (115.28 g m−2 in the estuarine stands and 513.88 g m−2 in the island-fringing stands). These variations may be attributed to the differences in tidal flushing and influence of freshwater in the two localities.