Adaptions of tree individual morphology and stem wood density to multiple climate and soil characteristics gradients

The tree height–diameter at breast height (H–DBH) and crown radius–DBH (CR–DBH) relationships as well as wood density are key for forest carbon/biomass estimation, parameterization in vegetation models and vegetation–atmosphere interactions. Although the H–DBH relationship has been widely investigated on site or regional scales, and a small amount of studies have involved CR–DBH relationships based on plot-level data, few studies have quantitatively verified the universality of these two relationships on a global scale. Moreover, in current Earth System Models/Dynamic Global Vegetation Models (ESMs/DGVMs), wood density is also oversimplified, being defined either as a uniform constant or as plant functional type-dependent (PFT-dependent) constants worldwide. Such oversimplifications may lead to simulation biases in morphology of woody PFTs, ecosystem transition and vegetation-atmosphere interactions. In our study, the ability of 29 functions to fit the H–DBH and CR–DBH relationships for six different plant functional types (PFTs) are evaluated on a global scale, based on a global plant trait database. Then, the relationships between H-DBH, CR-DBH, wood density and climate are investigated. This work provides a valuable foundation for parameterization improvements in vegetation models, and some clues to forest field investigations.