Flowering phenology in the subarctic shows earlier flowering species are less variable

Abstract:

Phenological studies are rarely reported from arctic and subarctic regions, but projections suggest that these ecosystems might be subject to rapid warming. Here, we present a phylogenetic analysis of flowering phenology across an elevational gradient in the Canadian subarctic. We show that the timing of first flower is best explained by a combination of snowmelt, elevation and growing degree days. However, we also show that early flowering species have lower intraspecific variability in their response to climate cues in comparison with late flowering species. Previous work has suggested that early flowering species are more variable in their phenology, but 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 variability in first flower between seasons over several years demonstrates an opposite trend to variability in first flower over a single growing season, but the underlying mechanisms are the same. 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 to late flowering species. These same species may show large variance between years reflecting interannual variation in climate.