Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities

TLDR

Recent studies using repeat photography, long‑term monitoring, and dendrochronology have documented shrub expansion across arctic, high‑latitude, and alpine tundra, which is expected to alter ecosystem structure, energy fluxes, and biogeochemical exchanges. The study synthesizes existing evidence, develops a conceptual framework for shrub expansion, and outlines future research priorities to project rates and understand ecosystem feedbacks. The authors construct a conceptual framework linking warming, altered snow cover, permafrost thaw, fire, anthropogenic activity, and herbivory changes as mechanisms driving shrub abundance. Satellite data show that increased Arctic greenness coincides with rising temperatures and is partly driven by shrub expansion.

Abstract

Abstract Recent research using repeat photography, long-term ecological monitoring and dendrochronology has documented shrub expansion in arctic, high-latitude and alpine tundra ecosystems. Here, we (1) synthesize these findings, (2) present a conceptual framework that identifies mechanisms and constraints on shrub increase, (3) explore causes, feedbacks and implications of the increased shrub cover in tundra ecosystems, and (4) address potential lines of investigation for future research. Satellite observations from around the circumpolar Arctic, showing increased productivity, measured as changes in ‘greenness’, have coincided with a general rise in high-latitude air temperatures and have been partly attributed to increases in shrub cover. Studies indicate that warming temperatures, changes in snow cover, altered disturbance regimes as a result of permafrost thaw, tundra fires, and anthropogenic activities or changes in herbivory intensity are all contributing to observed changes in shrub abundance. A large-scale increase in shrub cover will change the structure of tundra ecosystems and alter energy fluxes, regional climate, soil–atmosphere exchange of water, carbon and nutrients, and ecological interactions between species. In order to project future rates of shrub expansion and understand the feedbacks to ecosystem and climate processes, future research should investigate the species or trait-specific responses of shrubs to climate change including: (1) the temperature sensitivity of shrub growth, (2) factors controlling the recruitment of new individuals, and (3) the relative influence of the positive and negative feedbacks involved in shrub expansion.