Intra- and interspecific tree growth rates across a broad climate gradient: Toward a general metabolic scaling model linking climate, functional traits, and individual plant growth

Background/Question/Methods

Temperature and precipitation are considered primary drivers of variation in plant growth rate.  However, recent studies suggest that much of this variation might instead reflect variation in growing season length, plant size, and/or local adaptation or acclimation of plant functional traits.  We assessed these hypotheses by: (1) extending metabolic scaling theory to include hypothesized relationships between climate variables (temperature, precipitation, and length of growing season) and key plant functional traits (net carbon assimilation rates, specific leaf area, wood density, and leaf mass allocation) to predict rates of biomass production and stem diameter growth of individual plants, and (2) assessing these relationships within and across 33 woody plant species using functional trait and allometry data compiled from the literature with climate and tree diameter growth data collected from a  network of dendrometers across a broad temperate climate gradient.

Results/Conclusions

Annual rates of diameter growth and biomass production were more variable within individuals and among sites than across species and sites. Our results show that comparing the mass-normalized annual rates of biomass production per individual reveals a remarkable overlap across sites.  Nonetheless, in contrast to expectations, mass-normalized growth rates do exhibit marginally negative correlations with temperature and precipitation, suggesting that production per unit biomass may actually be higher in colder and drier climates than in hotter, wetter climates.  These results suggest that woody plants across broad climatic gradients may converge to a similar mass-normalized growth rate and possibly exhibit counter-gradient patterns of biomass production.  Extension of metabolic scaling theory suggests that these patterns may emerge from directional shifts in specific functional traits across climate gradients.