Present status of small-scale exploitation of mangroves in Rekawa Lagoon, Sri Lanka
V.T.K. Dayarathne , M.P. Kumara
Small-scale forest exploitation is reported to have significant impacts on the composition, structure, and regeneration of terrestrial forest types nevertheless, only a few studies have examined mangroves in this respect. Although information related to small-scale harvesting activities in mangroves helps management and conservation initiatives, such information is scanty for Sri Lanka. In order to address this knowledge gap, mangrove cutting/removal data were collected from Boraluwa mangrove community of Rekawa Lagoon (6°03’N 80°50’E), Sri Lanka from 4 transects (30m long, 10m wide; divided into 10 m x 10 m sub-plots) laid perpendicular to the shoreline, in July -December, 2012. The percentage cutting observed during the time ranged from 0% to 17% between the sub-plots while Aegiceras corniculatum and Lumnitzera racemosa were found to be cut at a higher intensity (10% and 21% respectively). Other mangrove species: Rhizophora mucronata, Excoecaria agallocha and Bruguiera gymnorrhiza reported only 1.0%, 1.3% and 4.2% cutting intensities respectively. Thus the highly vulnerable species for cuttings were A .corniculatum and L. Racemosa. However, Kruskal–Wallis test did not show a significant difference of cutting intensities between the sub-plots (S = 2.20, p > 0.05). The mean height of stems removed by cutting was 48.5 cm (±34.8) and 62.9 cm (±44.7) for A. corniculatum and L. Racemosa respectively while 5.7 cm (±3.35) and 5.2 cm (±2.5) were their mean diameters respectively. The mean % sprouting of the cut stumps in the transects were 42%, for A. corniculatum and it was 68% for L. racemosa. The mean number of sprouts (±SD) per stump were 5.9 (±4.5) and 4.3 (±3.2) for A. corniculatum and L. racemosa respectively. Only 8% of intact trees of both A. corniculatum and L. racemosa were with diameters larger than 8 cm indicating that larger stems of these two species have been selectively cut in the recent past. As the tree diameter is proportional to the age of the trees, even small scale cutting could affect the age composition and reproductive capacity of the mangrove forests in Rekawa lagoon.
Keywords: Mangrove cutting, Sprouting, Rekawa lagoon, Sri Lanka