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Permanent link (DOI): https://doi.org/10.7939/R33K79

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Shrub encroachment in arctic and alpine tundra: Patterns of expansion and ecosystem impacts. Open Access

Descriptions

Other title
Subject/Keyword
ecosystem function
Arctic
climate change
shrubs
willows (Salix spp.)
tundra
Yukon Territory
alpine
canopy
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Myers-Smith, Isla H.
Supervisor and department
Hik, David S (Biological Sciences)
Examining committee member and department
Cahill, J. C. (Biological Sciences)
Kershaw, G. Peter (Earth & Atmospheric Sciences)
Cook, Janice E. K. (Biological Sciences)
Department
Department of Biological Sciences
Specialization

Date accepted
2011-10-03T22:08:59Z
Graduation date
2011-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
With a warming climate, northern ecosystems will face significant ecological changes such as permafrost thaw, increased frequency of forest fires, and shifting ecosystem boundaries including the spread of canopy-forming shrubs into tundra communities. A growing number of observations show increases in canopy-forming shrubs at sites around the circumpolar Arctic, which could cause major modifications to the diversity and functioning of tundra ecosystems. In this study of changes in willow (Salix spp.) cover and abundance in tundra ecosystems of the Yukon Territory, I found evidence that canopy-forming willow patches have expanded and canopy heights have increased on Herschel Island and that willows have advanced upslope to extend their altitudinal ranges in the Kluane Region. The growth of these willows is temperature sensitive, with early growing season temperatures explaining approximately half of the variation in annual growth rings. I conducted an experimental manipulation of shrub canopy cover that demonstrated that canopies significantly influenced soil temperatures. Snow trapping by shrub canopies insulated soils in winter, and shading by canopies in summer kept soils cool under shrub cover. The experimental manipulations of artificial canopies and canopy removals functioned similarly to the unmanipulated treatments, indicating that the shrub canopy is the dominant control of soil temperatures in this system. I did not, however, observe many significant differences in the nutrient cycling parameters that I measured, and this indicates that the direct effects of shrub canopies on soil temperatures are weak controls over the carbon and nitrogen fluxes at this study site. Understanding both the rate of change in canopy forming woody shrubs and the impacts of this change on ecosystem function will improve projections of future carbon storage, permafrost integrity and wildlife habitat in tundra ecosystems.
Language
English
DOI
doi:10.7939/R33K79
Rights
License granted by Isla Myers-Smith (myerssmi@ualberta.ca) on 2011-10-03T02:35:49Z (GMT): Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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