Rising temperatures have begun to shift flowering time, but it is unclear whether phenotypic plasticity canaccommodate projected temperature change for this century. Evaluating clines in phenological traits and the extentand variation in plasticity can provide key information on assessing risk of maladaptation and developing strategiesto mitigate climate change. In this study, flower phenology was examined in 52 populations of big sagebrush (Artemi-sia tridentata) growing in three common gardens. Flowering date (anthesis) varied 91 days from late July to lateNovember among gardens. Mixed-effects modeling explained 79% of variation in flowering date, of which 46% couldbe assigned to plasticity and genetic variation in plasticity and 33% to genetics (conditional R2= 0.79, marginalR2= 0.33). Two environmental variables that explained the genetic variation were photoperiod and the onset ofspring, the Julian date of accumulating degree-days >5 °C reaching 100. The genetic variation was mapped for con-temporary and future climates (decades 2060 and 2090), showing flower date change varies considerably across thelandscape. Plasticity was estimated to accommodate, on average, a 13-day change in flowering date. However, theexamination of genetic variation in plasticity suggests that the magnitude of plasticity could be affected by variationin the sensitivity to photoperiod and temperature. In a warmer common garden, lower-latitude populations havegreater plasticity (+ 16 days) compared to higher-latitude populations (+10 days). Mapped climatypes of floweringdate for contemporary and future climates illustrate the wide breadth of plasticity and large geographic overlap. Ourresearch highlights the importance of integrating information on genetic variation, phenotypic plasticity and climaticniche modeling to evaluate plant responses and elucidate vulnerabilities to climate change.
