Regional variation in green-up timing along a caribou migratory corridor: Spatial associations with snowmelt and temperature

Spring green-up in arctic and alpine systems is predominantly controlled by temperature and snowmelt timing preceding and during the growing season. Variation in the timing of green-up across space is an important aspect of resource variability with which mobile herbivores must contend. Here, we measure the explanatory power of abiotic drivers of green-up in a Low Arctic region of west Greenland, host to a migratory caribou population. We identify inconsistent relationships between green-up and abiotic drivers across space. Whereas green-up timing is most closely related to snowmelt in some areas, in others it is most closely related to spring temperature. The negative correlation between the explanatory power of snowmelt and temperature suggests that at broad scales, where green-up is more constrained by snow cover, such as moist, mountainous coastal areas, it is less constrained by temperature. Where snow is less persistent through winter, such as cold, dry inland areas, temperature becomes the predominant factor driving green-up. If the principal driver of spring plant growth is inconsistent across a region, long-term trends in resource phenology could vary spatially. For seasonal migrants like caribou, synchronizing migration timing with resource phenology may be complicated by discordant interannual change across drivers of green-up timing.