Disentangling contributions of allometry, species composition and structure to high aboveground biomass density of high-elevation forests

The high elevation forests of the Central Himalayas include stands with an exceptional abundance of aboveground biomass, standing as some of the most carbon-rich forests in the entire Himalayan range and beyond. National or regional models, however, are inadequate in capturing this extreme concentration of biomass observed in select forest inventory plots. We aimed to identify factors contributing to the significant variability of biomass and thus, aboveground forest carbon in the high mountain forests of Nepal. By comparing the utilization of pantropical and Nepali allometric equations, we evaluated whether the elevational gradients in forest biomass were robust to changes in the allometric models used to predict plot biomass. Irrespective of the model employed, the highest biomass values were found in high elevation plots. The diverse distribution of forest biomass reinforces established size-density relationships, attributing observed variations to the interplay between tree size and density. Our results contribute valuable insights into these high biomass forests, affirming observed elevational gradients, quantifying the impact of tree species and structure, and elucidating factors influencing biomass sites concerning allometric models.