Plant Diversity, Aboveground Biomass and Carbon Stock in an Isolated Tropical Sub Montane Forest in Sri Lanka

This study was conducted at Rilagala conservation forest, Nawalapitiya to assess and compare the plant diversity, above ground biomass and carbon stock in the periphery and interior of an isolated sub montane forest in Sri Lanka. All trees above 5 cm Diameter at Breast Height (DBH) in eleven randomly demarcated 25 m × 25 m plots were recorded. Distance up to 100 m from the forest boundary considered as the periphery (8 plots) and over 200 m as the core (3 plots). A total of 1,583 trees belonging to 29 species were recorded and aboveground biomass (AGB) and carbon stocks were calculated using allometric equations. The tree diversity of each plot was calculated using the Shannon diversity index (H’). Results were statistically analysed using single factor ANOVA. The species richness and H’ were the highest at the periphery (n=23, H’= 2.55) while the lowest at forest interior (n=11, H’= 1.97). The highest tree density was recorded at periphery (2,992 trees ha-1) and it decreased to 1,408 trees ha-1 towards the core. The average DBH was 8.5 ± 3.33 cm and it increased towards the forest interior (9.7 ± 4.51 cm) from the periphery (7.2 ± 3.74 cm). Estimated aboveground biomass ranged from 63.99 - 108.13 Mg ha-1 with a mean of 82.53 ± 14.39 Mg ha-1. The above ground C stock was estimated from 31.99 - 54.07 Mg ha-1 with a mean of 41.26 ± 7.2 Mg ha-1. However, there was no significant difference between forest periphery and core in variables, except species richness (p<0.05). The study revealed that the diversity and density of trees decreased towards the forest interior and vice versa was recorded for DBH, AGB and carbon stock. The study highlights the importance of conserving isolated tropical sub montane forest patches for carbon sequestration.