Abstract
Climate change is testing the resilience of forests worldwide pushing physiological tolerance to climatic extremes. Plant functional traits have been shown to be adapted to climate and have evolved patterns of trait correlations (similar patterns of distribution) and coordinations (mechanistic trade‐off). We predicted that traits would differentiate between populations associated with climatic gradients, suggestive of adaptive variation, and correlated traits would adapt to future climate scenarios in similar ways.We measured genetically determined trait variation and described patterns of correlation for seven traits: photochemical reflectance index (PRI), normalized difference vegetation index (NDVI), leaf size (LS), specific leaf area (SLA), δ13C (integrated water‐use efficiency, WUE), nitrogen concentration (NCONC), and wood density (WD). All measures were conducted in an experimental plantation on 960 trees sourced from 12 populations of a key forest canopy species in southwestern Australia.Significant differences were found between populations for all traits. Narrow‐sense heritability was significant for five traits (0.15–0.21), indicating that natural selection can drive differentiation; however, SLA (0.08) and PRI (0.11) were not significantly heritable. Generalized additive models predicted trait values across the landscape for current and future climatic conditions (>90% variance). The percent change differed markedly among traits between current and future predictions (differing as little as 1.5% (δ13C) or as much as 30% (PRI)). Some trait correlations were predicted to break down in the future (SLA:NCONC, δ13C:PRI, and NCONC:WD).Synthesis: Our results suggest that traits have contrasting genotypic patterns and will be subjected to different climate selection pressures, which may lower the working optimum for functional traits. Further, traits are independently associated with different climate factors, indicating that some trait correlations may be disrupted in the future. Genetic constraints and trait correlations may limit the ability for functional traits to adapt to climate change.
Highlights
Forests are under pressure from climate change (Bonan, 2008; Canadell & Raupach, 2008; Chazdon, 2008; Riitters et al, 2002), and impacts are expected to reduce long-term resilience and function (Chazdon, 2008)
Traits are independently associated with different climate factors, indicating that some trait correlations may be
Understanding mechanistic patterns of plant traits that undergo processes of natural selection can broadly enhance our understanding of species distributional predictions to inform maintenance of forest ecosystem function under future climate scenarios
Summary
Forests are under pressure from climate change (Bonan, 2008; Canadell & Raupach, 2008; Chazdon, 2008; Riitters et al, 2002), and impacts are expected to reduce long-term resilience and function (Chazdon, 2008). Functional traits of tree species are indicative of patterns of adaptation to their environment (Reich, 2014), and the relationship between climate and some traits is well established (Wright et al, 2005). Functional traits, by definition, are indicative of their relationship to the environment (Shipley et al, 2016), and population differentiation along climate gradients can be used to quantify the relative contribution of climate variables to patterns of trait differentiation (Madani et al, 2018) These outputs would be unable to estimate the relative trait responsiveness to selection pressures. Measuring variation in functional traits, estimating their heritability, and identifying possible agents of selection in a foundation tree can provide critical information in how a species might continue to persist in a changing climate. We discuss the implications for the capacity to adapt to climate change and the ability to predict the coevolutionary trajectories of functional traits
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