Contrasting shrub species respond to early summer temperatures leading to correspondence of shrub growth patterns

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.

Retrospective growth analysis of the dwarf shrub Cassiope tetragona allows local estimation of vascular plant productivity in high arctic Svalbard

“…A similar conclusion was reached by Weijers et al. () for two contrasting shrubs, Cassiope and Salix pulchra , in an alpine tundra site in northwest Canada. In both cases, Cassiope and other plant species from a range of habitats showed a positive growth response to summer temperature (Van der Wal & Stien, ; Weijers et al., ).…”

“…() for two contrasting shrubs, Cassiope and Salix pulchra , in an alpine tundra site in northwest Canada. In both cases, Cassiope and other plant species from a range of habitats showed a positive growth response to summer temperature (Van der Wal & Stien, ; Weijers et al., ). This temperature response of Cassiope has been widely reported from both the Norwegian and Canadian high Arctic (Rayback & Henry, ; Weijers et al., and references therein).…”

A warmer and greener cold world: summer warming increases shrub growth in the alpine and high Arctic tundra

“…Yet, at both alpine sites, we found a stronger relationship between summer climate and growth for the evergreen shrub species studied. In addition, annual growth of C. tetragona has been shown to correspond to greening over a larger region of Yukon-Alaskan alpine tundra, as observed by remotely sensed normalized difference vegetation index (NDVI), than S. pulchra (WeijerS et al 2018). The weaker response to summer climate of B. nana at Vole, Norway, may be explained by higher grazing pressure, as expansion of B. nana, and not E. hermaphroditum has been shown to be inhibited by herbivory in an exclosure experiment in the Scandinavian mountains (VoWleS et al 2017).…”

“…Only C. tetragona from Pika may not fit this pattern, given its high ∆AIC-value as this site. However, at Pika, C. tetragona grows pre-dominantly at locations with long lasting snow cover, and hence early growing season temperatures may be crucial there in determining growing season length (WeijerS et al 2018).…”

“…Here, the deciduous tall shrub Salix pulchra was sampled late August 2007 (see MyerS-SMitH and HiK 2018 for more details), and the evergreen dwarf shrub Cassiope tetragona at the end of the growing season of 2010 (see WeijerS et al 2018 for more details). Cassiope tetragona (L.) D. Don.…”