The Siberian tundra is one of the key permafrost regions in the Arctic because of its large spatial extent and carbon-rich yedoma soils. Changes in permafrost thaw and concomitant carbon losses to the atmosphere can have large impacts on the global climate. Permafrost thaw is believed to strongly increase this century as a result of predicted increasing air temperature. At the same time Arctic vegetation growth and composition is predicted to respond to future climate change, which can have large implications for the stability of permafrost and can feedback to further vegetation changes. Deciduous shrubs are expected to benefit most from climate warming by increasing growth and expanding their range to higher latitudes, which may protect permafrost from thawing through shading of the soil surface. However, observational evidence for recent increases in deciduous shrub cover in the Arctic region is limited thus far to areas in Alaska. We examined if deciduous shrubs at our research site in the Indigirka lowlands, Northeastern Siberia, show a growth response to the main climate variables, temperature and precipitation. We constructed tree-ring width chronologies for two key Arctic deciduous shrub species, Betula nana and Salix pulchra, dating back roughly 60 years. The ring widths records are compared to summer-warmth index and summer-precipitation data from the closest climate station in order to detect the climate factor that mainly determines shrub growth. Remote sensing data are used to assess changes in Arctic vegetation productivity on a larger scale and to determine the relation between vegetation productivity and the main climate variables. Using a combined approach of dendrochronology and remote sensing data techniques provides the opportunity to study integrate the vegetation response at different spatial scales.

Results/Conclusions Our results indicate that growth of Salix pulchra shrubs corresponds positively to summer warmth and summer precipitation. Arctic vegetation productivity data from the last 25 years shows a clear positive trend in vegetation productivity, especially in shrub tundra areas. Arctic vegetation productivity trends show a good relationship with the individual shrub response to climate change. Together, these results indicate that Arctic greening is likely to continue under the current climate scenarios and that shrubs may be responsible for a large part of this Arctic greening.