High‐arctic plants like it hot: a long‐term investigation of between‐year variability in plant biomass

Abstract

The Arctic is viewed as most sensitive to climate warming and subject to a general greening. Yet, summer weather conditions, which differ greatly among years, are believed to have little direct effect on arctic plant productivity. The dominant view is that between‐year variation in aboveground plant biomass is small and poorly related to weather conditions in the same year in the Arctic. Here, we test this view based on a 12‐year investigation of peak plant biomass among habitats, plant functional types, and species in high‐arctic Svalbard.Our study revealed twofold variation (range 23–46 g/m2) in plant biomass between years, this being strongly related to summer temperature (r = 0.92). Importantly, we found strong plant biomass–summer temperature relationships across habitats, plant functional types, and species, and little evidence for a lagged effect of previous year's biomass. Responses were of similar orders of magnitude, indicating that summer weather conditions were the key driver of plant productivity at all three levels of investigation.We propose three key factors behind such tight relationships between summer temperature and plant biomass in the same year. First, our methodological approach, a combination of nondestructive shoot density estimates in small, permanent plots and destructive shoot mass estimates outside these plots, allowed us to overcome the otherwise overwhelming small‐scale spatial heterogeneity in aboveground plant biomass typical for high‐arctic tundra vegetation. Second, the high‐latitude location (78° N) makes the vegetation most susceptible to temperature differences due to their influence on process rates. Third, Svalbard's oceanic nature dictates prevalent cloud cover, making summer temperature a good proxy for light availability and thus an index of photosynthetic activity required for plants to produce biomass.The present study challenges the prevailing notion that relationships between summer weather and vascular plant performance in the Arctic are weak and highly variable among plant species. This has important implications for our understanding of how and at which temporal scales future climate change will shape arctic plant productivity and, in turn, the dynamics of other ecosystem components in the low‐productivity, bottom‐up regulated ecosystems of the High Arctic.