Rapid climate warming in the tundra biome has been linked
to increasing shrub dominance1–4. Shrub expansion can modify
climate by altering surface albedo, energy and water balance,
and permafrost2,5–8, 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.