BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-8-1169-2011 What are the main climate drivers for shrub growth in Northeastern Siberian tundra? Blok D. 4 1 Sass-Klaassen U. 2 Schaepman-Strub G. 3 Heijmans M. M. P. D. 1 Sauren P. 2 1 Berendse F. 1 Nature Conservation and Plant Ecology Group, Wageningen University, P. O. Box 47, 6700 AA, Wageningen, The Netherlands Forest Ecology and Forest Management, Wageningen University, P. O. Box 47, 6700 AA, Wageningen, The Netherlands Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland <i>Invited contribution by D. Blok, recipient of the EGU Young Scientists Poster Paper Award 2010.</i> 17 05 2011 8 5 1169 1179 Copyright: © 2011 D. Blok et al. 2011 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/8/1169/2011/bg-8-1169-2011.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/8/1169/2011/bg-8-1169-2011.pdf

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 <i>Salix pulchra</i> and <i>Betula nana</i> 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 <i>S. pulchra</i> (Pearson's <i>r</i> = 0.73, <i>p</i> < 0.001) and <i>B. nana</i> (Pearson's <i>r</i> = 0.46, <i>p </i>< 0.001). No effect of winter precipitation on shrub growth was observed. In contrast, summer precipitation of the previous year correlated positively with <i>B. nana</i> ring width (Pearson's <i>r</i> = 0.42, <i>p</i> < 0.01), suggesting that wet summers facilitate shrub growth in the following growing season. <i>S. pulchra</i> ring width correlated positively with peak summer NDVI, despite the small coverage of <i>S. pulchra</i> 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.

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