Abstract: Aims To develop regional allometric models for Hainan Island and assess the applicability of the widely used pantropical allometric model in estimating aboveground biomass (AGB, kg) for Hainan rainforests. Methods We used a dataset of 332 trees (117 species) from Hainan Island, with biomass data from aboveground, foliage, branch, and trunk. Standardized major axis regression was applied using diameter at breast height (D), tree height (H), and D²H as predictors to develop the regional model. We also estimated AGB using the pantropical model with wood density values matched at the species or genus level. The differences between observed and simulated AGB were compared for both the full dataset (332 trees) and a species-matched subset (92 trees), and the relationship between estimation bias and tree size was analyzed. Important findings (1) The regional models showed good fit (R² > 0.5), with better performance for AGB and trunk biomass (R² = 0.749–0.796), and weaker performance for foliage biomass (R² = 0.508–0.672). (2) No significant differences were found between observed and simulated AGB in both sample sets. However, estimation bias was negatively correlated with D, H, and D²H. In the species-matched sample set, the regression slopes were steeper, indicating that the AGB of larger trees was underestimated and that genus-level wood density substitution masked interspecific differences. (3) The regional model fitted to both observed and simulated AGB showed no significant differences in slope and intercept, the model developed based on observed AGB showed better prediction and extrapolation capabilities compared to the model developed using simulated data. The pantropical allometric model is applicable in Hainan; however, its reliability is limited by missing wood density data and the prevalence of large trees. Therefore, the regional model developed here should be the preferred approach for AGB estimation in Hainan under the current data constraints.

Key words: Allometric model, biomass estimation, pantropical allometric model, applicability assessment, Hainan Island