Deciduous shrubs are expected to rapidly expand in the Arctic during the coming decades due to climate warming.
A transition towards more shrub-dominated tundra may have large implications for the regional surface energy balance,
permafrost stability and carbon storage capacity, with
consequences for the global climate system. However, little
information is available on the natural long-term shrub
growth response to climatic variability. Our aim was to determine the climate factor and time period that are most important to annual shrub growth in our research site in NE-Siberia. Therefore, we determined annual radial growth
rates in Salix pulchra and Betula nana shrubs by measuring
ring widths. We constructed shrub ring width chronologies
and compared growth rates to regional climate and remotely
sensed greenness data. Early summer temperature was the most important factor influencing ring width of S. pulchra (Pearson's r=0.73, p<0.001) and B. nana (Pearson's r=0.46, p<0.001). No effect of winter precipitation on shrub growth was observed. In contrast, summer precipitation of the previous year correlated positively with B. nana ring width (Pearson's r=0.42, p<0.01), suggesting that wet summers facilitate shrub growth in the following growing season. S. pulchra ring width correlated positively with peak summer NDVI, despite the small coverage of S. pulchra shrubs (<5% surface cover) in our research area. We provide the first climate-growth study on shrubs for Northeast Siberia, the largest tundra region in the world. We show that two deciduous shrub species with markedly different growth
forms have a similar growth response to changes in climate.
The obtained shrub growth response to climate variability in
the past increases our understanding of the mechanisms underlying current shrub expansion, which is required to predict future climate-driven tundra vegetation shifts.