Scaling from individuals to forest communities and landscapes with models of juvenile tree growth and mortality

To understand and predict forest dynamics at community and landscape scales, I calibrated individual-based, resource-dependent, species-specific models of sapling growth and mortality for temperate and tropical forests.; At a whole-plant physiology scale, I found stored carbohydrates and low-light survivorship of saplings were positively correlated across four temperate tree species. A theoretical model provides an explanation: allocation to storage can enhance survivorship by buffering stresses (e.g. defoliation) while constraining plant size and associated respiratory and maintenance costs.; Variation in carbon balance (reflected in growth) is scaled to individual survivorship and community-level dynamics of Connecticut oak-transition northern hardwood forests. Mortality models as a function of recent growth show continuous interspecific variation; white ash exhibits two orders of magnitude higher mortality under suppressed growth than American beech. A spatially explicit forest dynamics model (SORTIE) demonstrates that interspecific differences substantially influence community dynamics and composition. Trade-offs among species in low-light survivorship versus high-light growth provides a simple generalization of community dynamics.; Landscape-level distribution of forest communities is predicted from site- and species-specific models of sapling mortality and light-dependent growth. Models were calibrated for similar species sets for a west-central Michigan and two Connecticut sites on contrasting soil types. Intraspecific variation in performance among sites directly affects site variation in canopy composition and interactions of species (e.g. competition), causing further compositional variation. Deciduous species varied among sites in mortality but not growth, and conifers in only growth. This dichotomy may simplify scaling from individuals to larger spatial scales.; To understand tropical forest dynamics and maintenance of tree species diversity, I modelled light-dependent mortality and growth for four tree species at La Selva Biological Station, Costa Rica. Significant interspecific differences in performance indicate tropical tree diversity is partly maintained by species specialization on light.; These studies demonstrate that mechanistic, individual-based models of plant performance can be scaled to make community predictions about succession, distribution of vegetation, and maintenance of diversity.