Advancing understanding of tropical forest carbon dynamics through improved allometric models for palms: A case study with Prestoea montana in Puerto

Abstract: Tropical forests are major components of Earth’s carbon stocks, but their diversity and structural complexity pose major challenges for making accurate estimates of their above ground biomass (AGB). Palms, in particular, are prominent and unique components of many tropical forests that have anatomical and physiological differences from dicot trees which affect their height - diameter allometry and consequently, our ability to accurately estimate their AGB. We focused on improving height estimates and AGB models for a highly abundant palm, Prestoea montana, in the Luquillo Forest Dynamics Plot, Puerto Rico. We measured stem height (Hstem), diameter at breast height (DBH) and basal diameter (DB) for 1215 individual palms. Although palms do not develop secondary xylem, we found a strong relationship both between Hstem:DBH and Hstem:DB for P. montana which indicates that its mechanical H:D scaling exhibits similar mechanical constraints of dicotyledonous trees. Additionally, we provide evidence that P. montana’s H:D allometry is mediated by several sources of environmental heterogeneity including slope, elevation, and neighborhood crowding (as a proxy for local competition). We applied our H:D allometric model to hindcast AGB dynamics in the Luquillo Forest Dynamics Plot. Finally, we demonstrated that neighborhood crowding has a negative effect on P. montana’s growth. Our study enables improved  estimates in Puerto Rico and provides novel insight to the growth dynamics of palms in tropical forests.