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Litter Production and Site Characteristics in Relation to Structure and Composition of Mangrove Forests in Ranong Province, Southern Thailand
Dissertation Abstract:
The study was conducted to determine the differences between mangroves at downstream and upstream of Klong Ngao, Ranong Province from 1 June 2001 to 31 May 2002. Two 200-m long transect lines in each site (downstream and upstream) were established from seaward margin to landward. Twenty 10 x 10 m2 plots were constructed in each transect line to study litter production stands structure, water salinity, and soil properties.
Results showed that mangroves downstream had a 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 and 597,495 stem/ha, respectively).
Average basal area and biomass downstream were 26.65 m2 /ha and 209.07 ton/ ha, respectively; whereas at upstream, 22.96 m2 /ha and 169.96 ton/ha, respectively. At downstream, average volume was 249.72 m3/ha while upstream, 207.3 m3/ha.
Water salinity of mangroves at downstream showed higher salinity than those at upstream in both wet and dry seasons. At downstream, water salinity was 22 and 33 ppt in wet and dry seasons, respectively while upstream, 18 and 30 ppt, respectively.
Mangrove soils at downstream were high in sand content while soils upstream were high 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 content at Ag, Cg1, and Cg2 horizons. However, for 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 Ag, Cg1, and Cg2 horizons between mangrove soils at downstream and upstream.
The average annual litter production at Transects 1 and 2 (downstream) were 9,552.5 and 9,399.7 kg/yr, respectively, while 8,639 and 10,781 kg/ha/yr for Transects 3 and 4 (upstream), respectively. Leaf litter fall consisted the major fractions, which ranged from 80.30 to 84.59 percent of the total litter fall. Litter fall reached 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 out 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 = 0.97876, P = 0.0007), and clay content of Ag horizon (r = 0.8313, P = 0.0403).
In the upstream, litter production had strong correlation and significantly different with soil reaction of Cg1 horizon (r = 0.8480, P = 0.0329), available phosphorus of Cg2 horizon (r = 0.8845), total nitrogen of Ag horizon (r = 0.8878, P = 0.0182), and clay content of Cg2 horizon (r = 0.9820, P = -0.0076).
Litter production and stand structure of mangroves at downstream were found to have strong correlation and were significantly different with density trees (r = 0.9981, P = 0.00202) while litter production had a weak correlation and insignificant difference with 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 was insignificantly different with density of sapling (r = 0.6025, P = 0.2056), tree diameter (r = 0.0242, P = 0.9637), tree height (r = 0.7596, P = 0.0798) and Shannon Index (r = 0.4122, P = 0.4167).