Evaluation of energetic equivalence across the Forest MacroSystems network

Abstract:

Metabolic scaling theory (MST) provides a mechanistic framework for predicting key features of plant community structure and biomass from first principles. Central to this framework is the decrease in the abundance of individuals as size increases. Specifically, MST predicts abundance will scale as the -2 power of size. MST also predicts that metabolic rates will scale with the 2 power of size. When combined, these relationships predict that total stand-level metabolic rates will scale as the 0 power of size. Thus, assuming that total community biomass production is the product of resource use and number of individuals within a size class, one important prediction of scaling theory is that biomass production does not vary with plant size – a phenomenon termed “energetic equivalence”. We tested the generality the size-frequency distributions and “energetic equivalence” predicted by allometric and metabolic scaling rules, respectively. To do this, we used a novel dataset from our Forest MacroSystems (FMS) network comprising up to 10 years of annual censuses for nine climatically and compositionally distinct forest communities. Our results highlight the universality of scaling rules, but illustrate how biotic and abiotic perturbations may cause departures from idealized theoretical scaling relationships. We discuss how these departures provide a mechanistic basis for explaining variation in forest biomass production. Ultimately, we demonstrate how simple allometric scaling rules can be applied to track global variation in forest biomass.