Litter production and site characteristics in relation to structure and composition of mangrove forests in Ranong Province, Southern Thailand

Results of the study showed that mangroves at downstream had higher value in number of species than those at upstream (17 species at downstream and 13 species at upstream). While average densities of trees (2,160 stem/ha), saplings (1,130 stem/ha) and seedlings (1,795 stem/ha) of mangroves at upstream had higher values than at downstream (1,640; 597; 495 stem/ha, respectively). Average basal area and biomass at downstream were 26.65 sq m/ha and 209.07 ton/ha, respectively whereas at upstream, 22.96 sq m/ha and 169.96 ton/ha. at downstream, average volume was 249.72 cu m/ha while at upstream, 207.30 cu m/ha. Water salinity of mangroves at downstream showed higher salinity than those at upstream in both wet and dry seasons. Mangrove soils at downstream were high in sand content while upstream soils in silt and clay contents. Both soils were high in organic matter, sulphur and other nutrients. In situ soil pH ranged from 6 to 8, but pH of air-dried soils was low (3.0-5.7). Thalassina mounds were common in landward zone. Mangrove soils at downstream and upstream were significantly different in sand, silt and clay contents at Ag, Cg1, and Cg2 horizons. However, for the chemical properties, such as pH (air-dried soils), electrical conductivity, organic matter, cation exchange capacity, total nitrogen, available phosphorus, exchangeable magnesium, sulphur and sodium were not significantly different at the Ag, Cg1 and Cg2 horizons between mangrove soils at downstream and upstream. Average annual liter production at downstream were 9,552.5 and 9,399.7 kg/ha/yr, respectively while at upstream had an average of 8,639.0 and 10,781 kg/ha/yr, respectively. Leaf litter fall consisted the major fractions which ranged from 80.30-84.59% of the total litter fall. Litter fall reached the peak in November in both sites of downstream and upstream. On the relationship between litter production and soil characteristics of mangroves at downstream, it was found that litter production had a strong correlation and significantly different with soil reaction of Ag horizon (r=0.8713, P=0.0238); soil reaction of Cg2 horizon (r=0.9929, P=0.0001); available phosphorus of Cg1 horizon (r=0.9786, P=0.0007) and clay content of Ag horizon (r=0.8313, P=0.0403). On the other site, at upstream litter production had a strong correlation and significantly different with soil reaction of Cg1 horizon (r=o.8480, P=0.0329); available phosphorus of Cg2 horizon (r=0.8845); total nitrogen of Ag horizon (r=o.8878, P=0.0182) and clay content of Cg2 horizon (r=0.9280, P=0.0076). Litter production and stand structure of mangroves at downstream was found to have a strong correlation and significantly different with the density of trees (r=0.9981, P=0.00202) while litter production had a weak correlation and non-significant difference with density of sapling (r=0.3650, P=0.4769); biomass (r=0.3586, P=0.4852) and Shannon Index (r=0.5079, P=0.3036). On the other site, at upstream, litter production had a weak correlation and significantly different with density of sapling (r=0.6025, P=0.2056); diameter of tree (r=0.0242, P=0.9637); height of tree (r=0.7596, P=0.0798) and Shannon Index (r=0.4122, P=0.4167)