Fig. 1: Two hypotheses explaining higher forest woody productivity in warmer forest stands in relation to inter-specific productivity-biomass relationships.

a The species response hypothesis assumes that tree species possess distinct productivity-biomass power-law relationships depending on temperature such that relative aboveground woody productivity p_i of species i tends to be higher in tropical versus temperate forests at the same species’ standing aboveground biomass B_i, leaving that frequency distribution of species biomass and per-stand species richness (SR) of each stand are the same among biomes. b The community structure hypothesis assumes that species possess similar productivity-biomass relationships regardless of temperature, i.e., species relative woody productivity p_i is not different between tropical and temperate species at the same species aboveground biomass B_i, while SR is larger and mean species biomass is smaller in tropical forest stands. Based on synthetic data generated assuming a bivariate normal distribution of ln p_i and ln B_i, with a common correlation slope (or, power-law exponent) of –0.15. Other coefficient values for generating random data are in Methods. Each of 10 stands in each forest has SR shown in right-hand panels. In the left-hand panels, the 95% prediction ellipses are shown in inter-specific p_i-B_i relationships. The right-hand panels show species-aggregated, stand-level woody productivity P = Σ_i p_i B_i and stand biomass B = Σ_i B_i, with predicted means and 95% confidence intervals of the power-law model fitting. All axes are on log scale. Source data are provided as a Source Data file.