Rapid climate warming in the tundra biome has been linked to increasing shrub dominance1,2,3,4. Shrub expansion can modify climate by altering surface albedo, energy and water balance, and permafrost2,5,6,7,8, yet the drivers of shrub growth remain poorly understood. Dendroecological data consisting of multi-decadal time series of annual shrub growth provide an underused resource to explore climate–growth relationships. Here, we analyse circumpolar data from 37 Arctic and alpine sites in 9 countries, including 25 species, and ∼42,000 annual growth records from 1,821 individuals. Our analyses demonstrate that the sensitivity of shrub growth to climate was: (1) heterogeneous, with European sites showing greater summer temperature sensitivity than North American sites, and (2) higher at sites with greater soil moisture and for taller shrubs (for example, alders and willows) growing at their northern or upper elevational range edges. Across latitude, climate sensitivity of growth was greatest at the boundary between the Low and High Arctic, where permafrost is thawing4 and most of the global permafrost soil carbon pool is stored9. The observed variation in climate–shrub growth relationships should be incorporated into Earth system models to improve future projections of climate change impacts across the tundra biome.
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We thank the many field and laboratory assistants for help with data collection, and the governments, parks, field stations and local and indigenous people for the opportunity to conduct research on their land. Financial support was provided by the International Arctic Science Committee (All), German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig (sTUNDRA working group), the EnviroNorth CREATE grant (I.H.M.-S.), International Polar Year Programs of the Government of Canada, Natural Sciences and Engineering Research Council of Canada and Northern Scientific Training Program (I.H.M.-S., D.S.H., M.V., S.A.R., N.B.-L., E.L., A.J.T., L.H., L.S.C., T.C.L.), INTERACT (262693), 7th Framework Programme, Virtual Institute ICLEA of the Helmholtz Foundation (M.W. and A.Buras), Wageningen University and Research Center, Darwin Center for Biogeosciences, Danish National Research Foundation (CENPERM DNRF100) (D.B.), Swedish Polar Secretariat (S.A.R.), Academy of Finland, Nordic Centre of Excellence TUNDRA, NASA Land Cover/Land-Use Change Program (B.C.F. and M.M.-F.), Natural Environment Research Council Independent Research Fellowship (NE/L011859/1) (M.M.-F.), Research Council of Norway (Project 212897) (J.D.M.S.), Fonds de recherche du Québec: Nature et technologies (N.B.-L., E.L., M.V.) and Centre d’études Nordiques, ArcticNet—a network of centres of excellence (S.A.R., N.B.-L., E.L., A.J.T., L.H., L.S.C.), Polar Continental Shelf Program (S.A.R., N.B.-L., E.L.), Canada Foundation for Innovation (T.C.L.), WSL Institute for Snow and Avalanche Research SLF (to C.R., M.A.D., J.A.W., S.Wipf), Knud Højgaard Charity Foundation (N.M.S.), The Northern Worlds initiative of the National Museum of Denmark (C.B.), IPY-NWO (project 851.40.051) (S.Weijers), Polish National Science Centre (project N306 009139) (A.Buchwal), Virtual Institute ICLEA of the Helmholtz Foundation (A.Buras), National Science Foundation (ARC-0806506) (A.T.N.), University of Zurich Research Priority Program ‘Global Change and Biodiversity’ (G.S.-S.), Woods Hole Research Center (K.C.G.), The Research Council of Norway (V.R.), EU ATANS Grant FP6506004 and the scholarship programme of the German Federal Environment Foundation (no. 20008/983) (M.H.).