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Modeling adaptive growth in forest trees: Integrating individual variation to understand climate responses in widely-distributed species
Article coécrit par Mélanie Saulnier
Individual trees show variable growth responses to climate, highlighting the importance of integrating individual-level variability to better predict forest resilience under climate change.
Abstract
An improved understanding of how forest trees may respond individually and differentially to climate across broad environmental gradients, due to adaptation or physiological acclimation, may facilitate more robust forecasts of forest resilience under climate change.
We present a framework for modeling stem diameter growth in adult canopy trees that accounts for responses to climate that may be unique for individuals in different ecological settings. We used data from > 10,000 tree cores from 888 forest inventory plots distributed across wide climatic gradients in two mountain ranges in Europe.
We formulated a suite of nonlinear models for each of the four species to understand factors regulating annual radial growth. The models accounted for the effects of tree ontogeny, competition, nitrogen deposition (Nd), temperature, and precipitation.
We compared two approaches to evaluate evidence for adaptation or acclimation in the growth–climate relations of trees. One method tested whether growth responses diverged for individual trees associated with distinct climate regimes. An alternate method fitted climate response functions with the deviation of climate in a given year from the prevailing average conditions at a tree location.
We also tested whether the peak height of this function, representing the maximum growth capacity of a tree, depended on local average climate. For all taxa, models that incorporated within-species variation received stronger support relative to simpler models that assumed a consistent species-average growth response to climate.
Growth in all but one species was best predicted by models fitted with climate deviations. Trees differed markedly in terms of their peak growth potential and climate optima, and in some cases, occupied suboptimal environments. Growth responses to nitrogen inputs were also modulated by climate.
Our framework offers a flexible approach for integrating individual-level climate sensitivity into tree demography models, which may allow for more rigorous investigations of forest dynamics, the outcomes of which may inform adaptive management strategies for mitigating climate change impacts.
