Forest biomass is helpful to assess its productivity and carbon (C) sequestration capacity. Several disturbance activities in tropical forests have reduced the biomass and net primary production (NPP) leading to climate change. Therefore, an accurate estimation of forest biomass and C cycling in context of disturbances is required for implementing REDD (Reducing Emissions from Deforestation and Forest Degradation) policy.

Biomass and NPP of trees and shrubs were estimated by using allometric equations while herbaceous biomass was estimated by harvest method. Fine root biomass was determined from soil monolith. The C stock in vegetation was calculated by multiplying C concentration to dry weight.

Total stand biomass (Mg·ha–1) in undisturbed forest stand (US) was 960.4 while in disturbed forest stand (DS) it was 449.1. The biomass (Mg·ha–1) of trees, shrubs and herbs in US was 948.0, 4.4 and 1.4, respectively, while in DS they were 438.4, 6.1 and 1.2, respectively. Total NPP (Mg·ha–1·yr–1) was 26.58 (equivalent to 12.26 Mg C·ha–1·yr–1) in US and 14.91 (6.88 Mg C·ha–1·yr–1) in DS. Total C input into soil through litter plus root turnover was 6.78 and 3.35 Mg·ha–1·yr–1 in US and DS, respectively.

Several disturbance activities resulted in the significant loss in stand biomass (53 %), NPP (44 %), and C sequestration capacity of tropical forest in eastern Nepal. The net uptake of carbon by the vegetation is far greater than that returned to the soil by the turnover of fine root and litter. Therefore, both stands of present forest act as carbon accumulating systems. Moreover, disturbance reflects higher C emissions which can be reduced by better management.