Abstract
The Arctic-alpine biome is warming rapidly, resulting in a gradual replacement of low statured species by taller woody species in many tundra ecosystems. In northwest North America, the remotely sensed normalized difference vegetation index (NDVI), suggests an increase in productivity of the Arctic and alpine tundra and a decrease in productivity of boreal forests. However, the responses of contrasting shrub species growing at the same sites to climate drivers remain largely unexplored.Here, we test growth, climate, and NDVI relationships of two contrasting species: the expanding tall deciduous shrub Salix pulchra and the circumarctic evergreen dwarf shrub Cassiope tetragona from an alpine tundra site in the Pika valley in the Kluane Region, southwest Yukon Territories, Canada.We found that annual growth variability of both species at this site is strongly driven by early summer temperatures, despite their contrasting traits and habitats. Shrub growth chronologies for both species were correlated with the regional climate signal and showed spatial correspondence with interannual variation in NDVI in surrounding alpine and Arctic regions. Our results suggest that early summer warming represents a common driver of vegetation change for contrasting shrub species growing in different habitats in the same alpine environments.
Highlights
Arctic-alpine ecosystems are sensitive to climate change (Settele et al 2014) and the rate of warming increases with latitude and elevation (Pepin et al 2015)
Our results suggest that early summer warming represents a common driver of vegetation change for contrasting shrub species growing in different habitats in the same alpine environments
Summer temperatures, which coincide with the time of year with maximum insolation, are warming across northwest North America and shrub growth chronologies for both species were correlated with the regional climate and showed spatial correspondence with interannual variation in Normalized Difference Vegetation Index (NDVI) in surrounding alpine and Arctic regions
Summary
Arctic-alpine ecosystems are sensitive to climate change (Settele et al 2014) and the rate of warming increases with latitude and elevation (Pepin et al 2015). Evidence from experimental warming (Walker et al 2006, Elmendorf et al 2012a), repeated vegetation surveys (Elmendorf et al 2012b), repeated photography (Sturm et al2001, Tape et al 2006), and dendrochronology (Myers-Smith et al 2011, 2015a), suggests that shrub growth is sensitive to summer warming and that shrub cover has increased in response to climate warming throughout the tundra biome. Pollen records indicate greater shrub dominance in tundra during past warm episodes in Late Quaternary North America (Hu et al 2002, Higuera et al 2008) and Russia (Velichko et al 1997). A growing number of studies indicate shrubline ecotone advance up- and north-ward into tall-shrub free tundra (Myers-Smith and Hik 2017). We do not yet know whether all shrub functional groups are responding to the rapidly warming tundra climate
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