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.

北极与高山生态系统的春季植被返青（spring green-up）主要受生长季前期及同期的气温与融雪时间调控。空间尺度上植被返青时间的差异，是移动植食动物需应对的资源可变性的重要维度。本研究针对栖息着迁徙驯鹿种群的格陵兰西部低北极（Low Arctic）区域，量化了植被返青的非生物驱动因子（abiotic drivers）的解释力。研究发现，不同区域内植被返青与非生物驱动因子间的关联并不一致：部分区域的植被返青时间与融雪关联性最强，而另一些区域则与春季气温关联最为紧密。融雪与气温的解释力呈负相关，这表明在植被返青更多受积雪制约的大尺度区域（如湿润多山的沿海区域），气温对返青的制约作用相对较弱；而在冬季积雪留存时间较短的区域（如寒冷干旱的内陆区域），气温则成为驱动植被返青的主导因子。若某一区域内春季植物生长的主导驱动因子存在空间异质性，那么该区域的资源物候（resource phenology）长期趋势也可能呈现空间差异。对于驯鹿这类季节性迁徙动物而言，若植被返青时间的各驱动因子的年际变化并不一致，那么其将迁徙时间与资源物候同步的行为可能会变得更为复杂。