Recent Growth and Expansion of Birch Shrubs Across a Low Arctic Landscape in Continental Canada: Are These Responses Mor
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Recent Growth and Expansion of Birch Shrubs Across a Low Arctic Landscape in Continental Canada: Are These Responses More a Consequence of the Severely Declining Caribou Herd than of Climate Warming? Rhett Andruko,1 Ryan Danby,2
and Paul Grogan1*
1
Department of Biology, Queen’s University, Kingston, Ontario K7L 3N6, Canada; 2School of Environmental Studies, Queen’s University, Kingston, Ontario K7L 3N6, Canada
ABSTRACT The recent widespread expansion of deciduous shrubs across much of the Arctic has been largely attributed to climate warming. This study investigated decadal growth rates of dwarf birch (Betula glandulosa) across a low Arctic landscape in the continental interior of Canada. Detailed birch cover (100 m2 replicate plots) and individual shrub stature measurement datasets for five representative habitat-types were compared between 2006 and 2016, and evaluated in relation to environmental
Received 2 August 2019; accepted 8 December 2019 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-019-00474-7) contains supplementary material, which is available to authorized users. All data in this study are accessible via the Polar Data Catalogue metadata website (https://www.polardata.ca). Authors Contributions PG conceived and designed the study. RA collected and analyzed the data. PG, RA, and RD wrote the manuscript. *Corresponding author; e-mail: [email protected]
characteristics. Furthermore, dendrochronologically-based annual growth rates were assessed in relation to the 20-year climate record. Birch height, lateral dimensions, and patch groundcover all increased 20–25% relative to 2006 values, but these increases were similar among the habitat-types. Together, the limited evidence of recent warming at this site, the absence of significant habitat-type growth rate differences, and the lack of correlation between annual climate and stem secondary growth strongly suggest that climate change was not the principal cause. Instead, we propose that release from caribou impacts following the recent severe herd decline may explain the net shrub growth. Individual shrub growth rates were correlated with soil nutrient availability, but the latter was highly variable, suggesting that growth rates are primarily determined by fine-scale rather than habitat-scale spatial heterogeneity in nutrient supply. Together, our results demonstrate that birch growth has been enhanced across a variety of habitat-types in the Daring Lake landscape over the decade since 2006, and suggest that the recent severe caribou herd declines may be at least as
R. Andruko and others significant as climate warming in driving birch shrub expansion in the Canadian central low Arctic.
Key words: birch; deciduous shrub; Arctic tundra; climate change; caribou; herbivory; trampling; groundcover; soil nutrients; soil moisture.
HIGHLIGHTS
often the physically dominant vegetation over much of the low Arctic, their increased growth could result in a number of important feedbacks, both within the e
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