Changing phenology and productivity in Arctic ecosystems has been widely observed over the last several decades and has profound implications for future ecosystem processes, carbon exchange, and quantity and quality of forage for migratory herbivores. However, despite their importance, the drivers of these changes are still not entirely understood, particularly the role of winter and early spring conditions in growing season vegetation dynamics. In this study we investigated the relationships between winter conditions and vegetation phenology and productivity across 6 tundra vegetation communities on Alaska’s North Slope from 2001 to 2017. We estimated annual timing of start, peak, and end of growing season and the total seasonal NDVI (time-integrated NDVI; TINDVI) from daily, 500-m resolution NDVI measurements. Date of snow-free ground, accumulated spring temperature and microbial ‘Active Days’ (the number of days with snow-soil interface temperature > -6°C) were estimated by SnowModel at the same spatial and temporal resolution. The relationship between vegetation phenology/productivity and winter/spring conditions was evaluated at 100 points within each vegetation community type, in regions of relatively homogeneous landscape cover within each pixel footprint.
Results/Conclusions
Our results highlight winter and spring conditions as important drivers of growing season vegetation dynamics in Arctic tundra, and demonstrate that some vegetation communities were more responsive to winter and spring conditions than others. Winter and spring conditions explain a larger amount of variation in the timing of start (40.6 - 78.6%) and peak of season (42.1 - 83.2%) than end of season (27.2 - 67.2%), with variation among vegetation communities. We found phenology was driven primarily by spring temperature in all vegetation types. In contrast, while 30.5 - 70.1% of the variation in productivity was explained by winter and spring conditions, productivity was driven by spring temperature in sedge-dominated communities, and Active Days in shrub-dominated communities. This study is one of few to evaluate the relative importance of different winter and spring drivers on growing season vegetation dynamics, or to investigate community-specific drivers of summer vegetation phenology and productivity. The results of this analysis suggest the relationship between winter and spring conditions and vegetation dynamics are community dependent, and that magnitude and pace of vegetation change in the Arctic in response to future climate may differ among vegetation types.