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__John Wesley Powell Center for Analysis and Synthesis
___Characterizing a link in the terrestrial carbon cycle: a global overview of individual tree mass growth
Summary 1. Metabolic scaling theory predicts that diameter growth rates of tree species are related to tree diameter by a universal scaling law. This model has been criticised because it ignores the influence of competition for resources such as light on the scaling of demographic rates with size. 2. We here test whether scaling exponents of abundant tropical tree species comply with the prediction of metabolic scaling theory and evaluate whether the scaling of growth with size depends on light availability. Light reaching each individual tree was estimated from yearly vertical censuses of canopy density, and a hierarchical Bayesian approach allowed quantifying confidence intervals for scaling exponents and accounting...
This table provides, for each of the 403 species used in our analysis, various documentary information as well as the fitted parameters for the relationship between mass growth rate and the natural log of tree size. The independent variable ln(mass) was divided into bins and a separate line segment was fitted to mass growth rate versus ln(mass) in each bin so that the line segments met at the bin divisions. Mass and growth rate were in megagrams (Mg) and Mg yr-1 respectively. Bin divisions were not assigned a priori but were fitted by the model separately for each species. We fitted models with 1, 2, 3, and 4 bins, and selected the model receiving the most support by Akaike’s Information Criterion for each species....
Tree growth and competition play central roles in forest dynamics. Yet models of competition often neglect important variation in species-specific responses. Furthermore, functions used to model changes in growth rate with size do not always allow for potential complexity. Using a large data set from old-growth forests in California, models were parameterized relating growth rate to tree size and competition for four common species. Several functions relating growth rate to size were tested. Competition models included parameters for tree size, competitor size, and competitor distance. Competitive strength was allowed to vary by species. The best ranked models (using Akaike’s information criterion) explained between...
Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations . Our ability to understand and predict changes in the forest carbon cycle--particularly net primary productivity and carbon storage--increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree , in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation)...
