Management implications
When local adaptation and phenotypic differentiation in forest trees are
closely tied to variation in climate, populations may become
increasingly maladapted as climate change continues (Shaw & Etterson
2012; Franks et al. 2014; Aitken & Bemmels 2015). However, the
magnitude of climate change combined with the degree of genetic
variability, heritability, and phenotypic plasticity of traits will all
interact to determine the extent of adaptation or maladaptation.
Maladaptation due to climate change is expected to be greatest in
populations from the warmest extent of their range, while populations at
the cold edge may benefit from slightly warmer temperatures (Aitken &
Bemmels 2015). This expectation corresponds with the maladaptive
phenological plasticity we have observed in southern populations vs.
adaptive phenological plasticity in northern populations (Cooperet al. 2019). However, nuanced changes in temperature and
precipitation patterns will produce novel genotype-climate associations,
creating more complex climate responses compared to the poleward range
shifts and vulnerable trailing edges traditionally associated with
warming (Gougherty et al. 2021). Although our study does not
encompass the full genetic and geographic range of Fremont cottonwood,
our results of declining performance as climate transfer distance
increases suggests that this species will likely experience
maladaptation as local conditions become more arid, especially for
southern populations that are close to their thermal tolerance (Aultet al. 2014; see Fig. 1). Because these trees are important
foundation species of riparian systems, selecting genotypes with
sufficient performance under warming conditions is essential for the
persistence of associated communities and ecosystems.