Factors affecting the tree and soil carbon stock in Shorea robusta Gaertn. forests along the elevational gradient in Eastern Nepal

Shorea robusta Gaertn. forest is a tropical or sub-tropical forest that has a good potential to store carbon. However, its capacity to store carbon can vary along the elevational gradient. The present study aimed to find the relationship between carbon stock and factors (edaphic, topographic, and physical) affecting it in S. robusta forests along an elevational gradient in eastern Nepal. The study was conducted in three community forests in Sunsari and Dhankuta Districts, which were regarded as lower, middle, and upper altitude forests, respectively. Altogether, 90 circular plots (30 in each forest) were laid for trees. Physico-chemical parameters (nitrogen, potassium, phosphorus, organic matter, moisture, pH, and bulk density) were analyzed from all 90 plots. The carbon stock in trees and soil ranged from 134 t ha−1 to 372 t ha−1 and 27.69 t ha−1 to 60.03 t ha−1, respectively. The tree carbon stock was higher in lower altitude forests. However, the highest soil carbon stock was recorded in the higher altitude forest. Potassium content and pH were positively correlated with the tree carbon stocks. However, organic matter, nitrogen content, and altitude negatively influenced the tree carbon stock. Nitrogen content and altitude positively affected the soil carbon stock. However, potassium content and pH had a negative relationship with soil carbon stock. It is clear that these forests have served as carbon storage facilities, and the potential to store carbon was influenced by edaphic, physical and topographic factors. This research advances our knowledge of how community-managed Sal forests can help to mitigate the consequences of climate change along an elevational gradient.