Carbon sink and source function of Eastern Himalayan forests: implications of change in climate and biotic variables

Forests serve as a sink and source of carbon and play a substantial role in regional and global carbon cycling. The Himalayan forests act as climate regulators of the Hindukush region, which is experiencing climate change at a high pace, and a proper understanding of these systems is necessary to mitigate this problem. We hypothesize that the variance of abiotic factors and vegetation will influence the carbon sink and source function of the different forest types of the Himalayas. Carbon sequestration was computed from the increment of carbon stocks estimated allometrically using Forest Survey of India equations, and soil CO2 flux was determined by the alkali absorption method. The carbon sequestration rate and CO2 flux by the different forests exhibited a negative relation. The carbon sequestration rate was highest with minimum emission in the temperate forest, while the tropical forest recorded the least sequestration and maximum carbon flux rate. The Pearson correlation test between carbon sequestration and tree species richness and diversity revealed a positive-significant influence but negative relation with climatic factors. An analysis of variance indicated significant seasonal differences between the rate of soil carbon emissions due to variations in the forest. A multivariate regression analysis of the monthly soil CO2 emission rate shows high variability (85%) due to fluctuations of climatic variables in the Eastern Himalayan forests. Results of the present study revealed that the carbon sink and source function of forests respond to changes in forest types, climatic variables, and edaphic factors. Tree species and soil nutrient content influenced carbon sequestration, while shifts in climatic factors influenced soil CO2 emission rate. Increased temperature and rainfall may further change the soil quality by enhancing soil CO2 emission and reducing soil organic carbon, thereby impacting this region's carbon sink and source function. Enhancing tree diversity in the forests of this region may be beneficial for retarding this impact.