Various environmental, management and biotic and abiotic factors determine forest types, regeneration, biomass, carbon and tree composition, structure, and diversity. Diachronic analysis of forest biomass and carbon stocks of 2014 and 2022 was carried out to assess the effect of assisted natural regeneration in the Living Mountain Lab (LML) of International Center for Integrated Mountain Development (ICIMOD), Nepal. A total of thirty permanent sample plots were laid in the natural dense and sparse forest stands following stratified random sampling. The site was enriched with 17,472±100.2 seedlings ha-1 indicating the excellent natural regeneration with the average tree density 1337±80.5 ha-1 and mean basal area 28.69±6.9 m2ha-1. The average forest biomass in 2022 was 200.73±65.2 t ha-1 and the most contribution was from trees (96 %). The mean net annual biomass increment was found to be 6.80 tha-1yr-1 and the open tree canopy with sparse strata contributed the most. The mean vegetation carbon was 98.31±10.3 t Cha-1 significantly contributed by trees. Thus, the large trees with open canopy contain significant amount of forest biomass and store more carbon as woody components and support species dynamics. Similar assessment of forest biomass and carbon has a potential to be linked with forest restoration with reference to regeneration, carbon sequestration and climate change mitigation.