Organic matter accumulation in hill forests of Chittagong region, Bangladesh

Abstract

Litter fall and its effect on forest soil properties at each decomposition stages were investigated in tropical monsoon climatic conditions of three plantations (7-year acacia plantation, 15-year acacia plantation and 18-year mixed plantation) and one natural forest (Sitapahar forest) from Chittagong hilly region of Bangladesh. Results showed that total accumulation of organic matter increased with plantation age, accompanying with a decrease of annual accumulation rate. Within the same vegetation type, the organic accumulation of both fresh and partially decomposed litter with humus varied significantly (p≤0.05) on hill positions, being highest on bottom slope and decreased gradually towards hilltop in the forest. Reverse trend in accumulation of soil organic matters was shown in 15-year Acacia auriculiformis plantation, from where fuel wood collected. In 7-and 15-year acacia and 18-year mixed broadleaved plantations, rates of total organic matter production consisting of fresh, partially and completely decomposed litter as well as incorporated organic matter in soil were 2554.31, 705.79 and 1028.01 kg⋅ha -1 ⋅a -1 , respectively, and the corresponding contribution from fresh litter were 38.23, 19.40 and 30.48 kg⋅ha -1 ⋅a -1 , respectively. In the three plantations and the natural forest, on an average fresh litter constituted 32.45%, partially decomposed litter with humus 13.50% and incorporated organic matter in soil 54.56% of the total organic matter production with mean litter thickness of 0.90 cm. Soil acidity increased with the increase of decomposition stage of organic matter.