Elevation, aspect, and climate shape blue pine (Pinus wallichiana) biomass and carbon dynamics in the Bhutanese Himalayas

Forests play a critical role in Bhutan's climate mitigation strategy, sequestering atmospheric carbon at a rate that enables the country to boast a net negative emissions status. Understanding how the complex topography and climate of Bhutan constrain tree growth is essential for managing this resource and predicting future responses to climate change. This study utilised dendrochronological and allometric techniques to explore how elevation (2200–3000 m) and aspect (north/south) influence the climate sensitivity of socio-economically important blue pine (Pinus wallichiana) in Western Bhutan and providing the first investigation into their influence on annual biomass accumulation. Total aboveground biomass (TAGB) and carbon accumulation rates were greater at lower elevations (2200–2400 m). Predicted peaks in TAGB and carbon accumulation occurred at 2350 m, averaging 24.5 and 11.5 kg tree⁻¹ year⁻¹, respectively. Mean TAGB accumulation rates were significantly greater on south-facing slopes (14.8 ± 6.5 kg tree⁻¹ year⁻¹) compared to the north-facing slopes (11.9 ± 5.2 kg tree⁻¹ year⁻¹). Dendroclimatic analysis and regression trees revealed April precipitation and late-season (August-September) minimum temperature to be major drivers of blue pine growth. These findings highlight topographically driven growth patterns useful for proactive management of blue pine.