Arctic tundra shrubification: a review of mechanisms and impacts on ecosystem carbon balance

Zelalem A Mekonnen, William J Riley, Logan T Berner, Nicholas J Bouskill, Margaret S Torn, Go Iwahana, Amy L Breen, Isla H Myers-smith, Mariana García Criado, Yanlan Liu, Eugénie S Euskirchen, Scott J Goetz, Michelle C Mack, Robert F Grant

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Vegetation composition shifts, and in particular, shrub expansion across the Arctic tundra are
some of the most important and widely observed responses of high-latitude ecosystems to rapid
climate warming. These changes in vegetation potentially alter ecosystem carbon balances by
affecting a complex set of soil–plant–atmosphere interactions. In this review, we synthesize the
literature on (a) observed shrub expansion, (b) key climatic and environmental controls and
mechanisms that affect shrub expansion, (c) impacts of shrub expansion on ecosystem carbon
balance, and (d) research gaps and future directions to improve process representations in land
models. A broad range of evidence, including in-situ observations, warming experiments, and
remotely sensed vegetation indices have shown increases in growth and abundance of woody
plants, particularly tall deciduous shrubs, and advancing shrublines across the circumpolar Arctic.
This recent shrub expansion is affected by several interacting factors including climate warming,
accelerated nutrient cycling, changing disturbance regimes, and local variation in topography and
hydrology. Under warmer conditions, tall deciduous shrubs can be more competitive than other
plant functional types in tundra ecosystems because of their taller maximum canopy heights and
often dense canopy structure. Competitive abilities of tall deciduous shrubs vs herbaceous plants
are also controlled by variation in traits that affect carbon and nutrient investments and retention
strategies in leaves, stems, and roots. Overall, shrub expansion may affect tundra carbon balances
by enhancing ecosystem carbon uptake and altering ecosystem respiration, and through complex
feedback mechanisms that affect snowpack dynamics, permafrost degradation, surface energy
balance, and litter inputs. Observed and projected tall deciduous shrub expansion and the
subsequent effects on surface energy and carbon balances may alter feedbacks to the climate
system. Land models, including those integrated in Earth System Models, need to account for
differences in plant traits that control competitive interactions to accurately predict decadal- to
centennial-scale tundra vegetation and carbon dynamics.
Original languageEnglish
Article number053001
JournalEnvironmental Research Letters
Issue number5
Publication statusPublished - 23 Apr 2021


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