Aboveground Carbon Stocks of Tropical Forests and Tree Plantations along an Elevational Gradient in the Western Ghats of Peninsular India: Doplant Diversity and Species Richness Impact Forest Carbon Stocks?

Biomass carbon (C) stocks and species richness and diversity are interlinked, and they co-vary along an elevational gradient. To test these hypotheses of inter-connectiveness and covariation in the Western Ghats (peninsular India) context, we enumerated 16 moist forest plots as well as 18 rubber (Hevea brasiliensis) and coconut (Cocos nucifera) plantations each. Our main objectives were to assess the aboveground biomass C (AGB-C) stocks and the association between plant diversity and forest AGB-C stocks along an elevation gradient. Species-specific allometric equations and Ordinary Kriging interpolation were used to predict and map AGB-C and species diversity. AGB-C stocks varied significantly among forest (381.69 ± 25.87 Mg ha–1), rubber (73.92 ± 7.76 Mg ha–1), and coconut (21.19 ± 1.23 Mg ha–1) stands. Forest AGB-C stocks also decreased linearly with increasing elevation. Although rubber and coconut AGB-C declined with elevation, the differences were not significant. The richness and diversity of arboreal species were higher in mid-elevation forests compared to low/high-elevation sites (unimodal pattern). With Simpson’s diversity index ranging from 0.695 to 0.865, Shannon index of 1.445–2.231, and Equitability of 0.883–0.994, our study sites exhibited moderate to high species diversity and encompassed 26 IUCN Red-listed species. Diversity and AGB-C were significantly correlated, indicating that the results support the hypothesis on inter-connectiveness. Overall, the forests at low and mid-elevations showed greater potential for C sequestration and biodiversity conservation, implying the need for adaptive management (designing actions) of these forests to mitigate the impending global climate change and conserve biodiversity.