Abstract
Abstract. 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.
Highlights
Climate change scenarios predict increasing air temperatures for the decades, with most warming occurring at high latitudes (IPCC, 2007)
Residual (RES) chronologies were established for the two shrub species, with the S. pulchra chronology showing higher inter-series correlation than the B. nana series (Table 1)
The large variability in ring width between B. nana individuals resulted in relatively low expressed population signal (EPS) values (0.58–0.83), especially in the early part of the B. nana residuals chronologies (RES) chronology (1948–1970)
Summary
Climate change scenarios predict increasing air temperatures for the decades, with most warming occurring at high latitudes (IPCC, 2007). Northern ecosystems will be greatly impacted by climate changes through alterations of the surface energy balance, permafrost thaw and changes in vegetation (ACIA, 2004). Vegetation changes have multiple feedbacks to the regional climate system through changes in the surface albedo, soil moisture exchange and the soil carbon balance (McGuire et al, 2006; Wookey et al, 2009). Of all plant functional types, deciduous shrubs are among the most responsive to changes in temperature by increasing their growth, as shown by many experimental warming studies across the Arctic (Chapin et al, 1995; Hobbie and Chapin, 1998; Walker et al, 2006). Circumpolar greening (Normalized Difference Vegetation Index, NDVI) trends suggest that shrub expansion is a widespread phenomenon across the Published by Copernicus Publications on behalf of the European Geosciences Union
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