Variation of Mangrove Above-ground Dry Biomasses in Relation to Anthropogenic Disturbances

Abstract

Estimations of Above-Ground Biomasses (AGB) assist determining the mangrove carbonstocks in the views of mitigating the increased atmospheric carbon. Such studies are rare inSri Lankan mangrove systems, particularly for Rekawa mangroves which is one of the primemangrove sites in the country. The current study applied a non-destructive, commonaboveground allmetric equation in to four 30m long mangrove transects (divided in to three10m × 10m blocks) of north mangrove community (06003’N 80050’E) of Rekawa Lagoon,Sri Lanka. For the equation, the diameter at the breast height of all the living mangrove treesand the diameter at the highest point of the cut stumps were recorded. Wood density valuesrequired for the equation were referred from literatures while for the mostly harvested (95%)Lumnitzer racemosa and Aegiceras corniculatum, the values (0.738±0.034 and 0.547±0.032gcm-3 respectively) were evaluated gravimetrically. The living AGB values (mean±SD) of thetransects (137.1±69.8, 201.8±102.6, 62.4±38.0 and 68.7±23.6 tha-1) were significantlydifferent between the transects (Friedman test: S = 8.20, DF = 3, p<0.05). The removed AGB(mean±SD) due to tree cuttings were 29.3±22.8, 6.4±8.7, 25.0±12.6 and 30.8±13.3 tha-1 forthe four transects and were not significantly different (Friedman test: S = 2.50, DF = 3,p>0.05). However, the % removal of biomass in the transects (19.7, 3.7, 34.3 and 31.79) weresignificantly different (Friedman test: S = 7.40, DF = 3, p<0.05) where these values were14.6, 2.9, 41.6, 0.0, 9.0, 2.3, 18.4, 16.4, 67.9, 34.2, 16.6 and 44.6 for the studied 12 plots.Thus, except in one plot, all other plots had experienced anthropogenic biomass removalwhere one plot had as high as 67.9% removal. The total Basal area (mean±SD) of the livingtrees four transects (37.0±16.1, 43.1±11.1, 22.1±13.5 and 19.4±7.4 m2 ha-1) show significantdifference (Friedman test: S = 8.20, DF = 3, P = 0.04). However, referring to, only twostudied blocks had relatively undisturbed forests with basal area >45 m2 ha−1 while degradedforest conditions were observed in another two plots having basal area <15 m2 ha−1. Thus, thecurrent study reviled notable anthropogenic AGB removal in Rekawa area where necessarymanagement actions need to be implemented to secure the mangrove carbon stocks.