The general form of the tree size distribution has been a topic of substantial recent interest. It has been argued that metabolic theory predicts a power-law relationship with an exponent of -2. However, demographic models suggest that this is only one of many outcomes that can result from simple growth-mortality processes. Most studies examining empirical tree size distributions focus on analyzing each distribution separately, comparing the general functional form and specific parameter values to different possible models. Here we take an alternative, macroecological, approach by evaluating hundreds of tree size distributions, treating each individual size distribution as a single observation, and looking at the general behavior of these distributions across spatial and temporal gradients.
Results/Conclusions

Exponents of fitted power laws exhibit a clear central tendency with values of the exponents clustering near -2. The variability in the exponents cannot be well explained using a suite of environmental data. Analyses of local scale dynamic data and geographic correlations suggest that observed variability in the form of the size distribution is driven by the successional stage of the forest plot.