Conclusions
By combining QST-FST analyses and
climate-trait regressions, we show that both quantitative traits and
associated plasticity are targets of climate-driven selection, where
population may exhibit significant differentiation in both, one, or
neither type of analysis (Table 4). This spectrum can help determine
which traits are likely under the strongest climate-drive selection.
Specifically, phenology as well as bud flush plasticity and height
plasticity show the strongest responses to selection (Table 4). These
traits and plasticities could be most impacted by further climate
change, as they show strong signals of climate-driven selection in the
past. However, both the detection of past selection and the
differentiation in current performance differed strongly across our
experimental common gardens. Strategies for management of widespread
species like Fremont cottonwood would benefit from considering the
climatic selection pressures of source locations to anticipate their
future performance, as well as the population-specific potential for
adaptive trait plasticity under changing environmental conditions.