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

• Author / Creator

  Myers-Smith, Isla H.

• 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.

• Subjects / Keywords

  • Yukon Territory
  • Alpine
  • Climate change
  • Willows (Salix spp.)
  • Canopy
  • Arctic
  • Shrubs
  • Tundra
  • Ecosystem function

• Graduation date

  Fall 2011

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R33K79

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.