Predicting flowering phenology in a subarctic plant community

Phenological studies are rarely reported from arctic and subarctic regions, but are essential to evaluate species' response to climate change in these rapidly warming ecosystems. Here, we present a phylogenetic analysis of flowering phenology across an elevational gradient in the Canadian subarctic. We found that the timing of first flower was best explained by a combination of snowmelt, elevation, and growing degree-days. We also show that early flowering species have demonstrated lower intraspecific variability in their response to climate cues in comparison with late flowering species, such that individual flowering times of early species are more closely tied to environmental predictors. Previous work has suggested that early flowering species are more variable in their phenology. However, these studies have mostly examined variation in phenology over time, whereas we examined variation in phenology over space. We suggest that both patterns can be explained by the tighter coupling between phenology and climate cues for early flowering species. Thus, early flowering species have low intraspecific variance in flowering times within a single growing season as individuals respond more uniformly to a common set of cues in comparison with late flowering species. However, these same species may show large variance between years reflecting interannual variation in climate.