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.