Analyses of growth response to resource availability are the basis for interpreting whether trophic trade‐offs contribute to diversity. If different species respond most to resources that are limiting at different times, then those differences may trade off with other trophic or life‐history traits that, together, help to maintain diversity. The statistical models used to infer trophic differences do not accommodate uncertainty in resources and variability in how individuals use resources. We provide hierarchical models for resource–growth responses that accommodate stochasticity in parameters and in data, despite the fact that causes are typically unknown. A complex joint posterior distribution taken over >102 parameters is readily integrated to provide a comprehensive accounting of uncertainty in the growth response, together with a small number of hyperparameters that summarize the population response. An application involving seedling growth response to light availability shows that large trophic differences among species suggested by traditional models can be an artifact of the assumption that all individuals respond identically. The hierarchical analysis indicates broad trophic overlap, with the implication that slow dynamics play a more important role in preserving diversity than is widely believed. Corresponding Editor: A. M. Ellison.
Summary• By altering foliage quality, exposure to elevated levels of atmospheric CO 2 potentially affects the amount of herbivore damage experienced by plants.• Here, we quantified foliar carbon (C) and nitrogen (N) content, C : N ratio, phenolic levels, specific leaf area (SLA) and the amount of leaf tissue damaged by chewing insects for 12 hardwood tree species grown in plots exposed to elevated CO 2 (ambient plus 200 µl l − 1 ) using free-air CO 2 enrichment (FACE) over 3 yr.• The effects of elevated CO 2 varied considerably by year and across species. Elevated CO 2 decreased herbivore damage across 12 species in 1 yr but had no detectable effect in others. Decreased damage may have been related to lower average foliar N concentration and SLA and increased C : N ratio and phenolic content for some species under elevated compared with ambient CO 2 . It remains unclear how these changes in leaf properties affect herbivory.• Damage to the leaves of hardwood trees by herbivorous insects may be reduced in the future as the concentration of CO 2 continues to increase, perhaps altering the trophic structure of forest ecosystems.
Decades of study on climatic change and its direct and indirect effects on forest ecosystems provide important insights for forest science, management, and policy. A synthesis of recent research from the northeastern United States and eastern Canada shows that the climate of the region has become warmer and wetter over the past 100 years and that there are more extreme precipitation events. Greater change is projected in the future. The amount of projected future change depends on the emissions scenarios used. Tree species composition of northeast forests has shifted slowly in response to climate for thousands of years. However, current human-accelerated climate change is much more rapid and it is unclear how forests will respond to large changes in suitable habitat. Projections indicate signifi cant declines in suitable habitat for spruce-fi r forests and expansion of suitable habitat for oak-dominated forests. Productivity gains that might result from extended growing seasons and carbon dioxide and nitrogen fertilization may be offset by productivity losses associated with the disruption of species assemblages and concurrent stresses associated with potential increases in atmospheric deposition of pollutants, forest fragmentation, and nuisance species. Investigations of links to water and nutrient cycling suggest that changes in evapotranspiration, soil respiration, and mineralization rates could result in signifi cant alterations of key ecosystem processes. Climate change affects the distribution and abundance of many wildlife species in the region through changes in habitat, food availability, thermal tolerances, species interactions such as competition, and susceptibility to parasites and disease. Birds are the most studied northeastern taxa. Twenty-seven of the 38 bird species for which we have adequate long-term records have expanded their ranges predominantly in a northward direction. There is some evidence to suggest that novel species, including pests and pathogens, may be more adept at adjusting to changing climatic conditions, enhancing their competitive ability relative to native species. With the accumulating evidence of climate change and its potential effects, forest stewardship efforts would benefi t from integrating climate mitigation and adaptation options in conservation and management plans.
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