Does biomass partitioning differ between woody plant functional types? Analysis of a global biomass and allometry database (BAAD)
Understanding how plants are plant constructed – i.e. how key size dimensions and the amount of mass invested in different tissues varies among individuals – is essential for modeling plant growth, estimating carbon stocks, and mapping energy-fluxes in the terrestrial biosphere. Although global vegetation models (GVMs) typically assume that the major woody plant functional types (PFTs) differ in biomass partitioning between leaves, stems and roots, empirical data have been lacking. Here we present the Biomass And Allometry Database (BAAD) for woody plants. BAAD contains 258526 measurements collected in 175 different studies, from 21084 individuals across 675 species. Most of these data are associated with an existing publication, however, raw data files were rarely made public at time of publication. Thus BAAD contains individual level data from different studies, transformed into standard units and variable names. The data comprise the major woody plant functional types, across nine vegetation types and three biomes. Variables included are total leaf area, area of stem cross-section, including sapwood, heartwood, and bark; height of plant and crown base, crown area and surface area; and the dry mass of leaf, stems, roots, and other components.
Using BAAD, we show that, after accounting for size-related shifts in biomass partitioning, major woody PFTs (evergreen gymnosperms, deciduous and evergreen angiosperms) do not differ in the amount of leaf area supported, but rather the amount of leaf mass per unit above ground biomass. Moreover, we find that these differences relate to systematic shifts in leaf mass per area, a leading trait within the leaf economics spectrum. In addition, we show how a second trait, leaf area per stem basal area, explains additional variation in biomass partitioning among species; however this trait does not differ systematically among major woody PFTs. Root-shoot ratios did not vary systematically between PFTs, nor did biomass partitioning differ appreciably with climate variables or biome. Combined, these results uncover fundamental rules in how plants are constructed and allow for systematic benchmarking of biomass partitioning routines in current GVMs.