University of SaskatchewanHARVEST
  • Login
  • Submit Your Work
  • About
    • About HARVEST
    • Guidelines
    • Browse
      • All of HARVEST
      • Communities & Collections
      • By Issue Date
      • Authors
      • Titles
      • Subjects
      • This Collection
      • By Issue Date
      • Authors
      • Titles
      • Subjects
    • My Account
      • Login
      JavaScript is disabled for your browser. Some features of this site may not work without it.
      View Item 
      • HARVEST
      • Electronic Theses and Dissertations
      • Graduate Theses and Dissertations
      • View Item
      • HARVEST
      • Electronic Theses and Dissertations
      • Graduate Theses and Dissertations
      • View Item

      Tree Ring Responses to Climate: Drought Stress Signals Decreased Resilience of Northern Boreal Forests

      Thumbnail
      View/Open
      WALKER-DISSERTATION.pdf (2.377Mb)
      Date
      2015-07-23
      Author
      Walker, Xanthe
      Type
      Thesis
      Degree Level
      Doctoral
      Metadata
      Show full item record
      Abstract
      Unprecedented rates of climate change have increased forest stress and mortality worldwide. Previous research in the boreal forest has largely documented negative growth responses to climate in forest species and habitats characteristic of drier conditions, emphasizing the sensitivity of drier or warmer landscape positions to climate warming. Tree growth responses to recent climate warming may signal changes in the susceptibility of forest communities to compositional change and consequently impact a wide range of ecosystem processes and services. In this study, I explored relationships between climate and radial growth of black spruce, a dominant tree species typical of cool and moist habitats in the boreal forests of North America. I assessed how growth-climate responses varied with stand characteristics and landscape position across four different regions in Alaska and Yukon Territory and found widespread negative correlations between growth and temperature. Decreased tree growth in association with increasing temperatures is generally accepted as a signal of temperature induced drought stress. However, variations in tree growth alone do not reveal the physiological mechanisms behind recent changes in tree growth. Thus, I used stable carbon isotopes to test if the changes in growth were due to physiological drought stress. My results highlight the prominence of drought stress in the boreal forest, even for trees located in cool and moist landscape positions. As mature trees might be able to survive in stressful environmental conditions that do not permit successful post-fire recruitment and survival of seedling, drought stress could affect the resilience of the boreal forest ecosystem to disturbance from fire. I assessed drought stress in pre-fire trees and used post-fire forest compositional changes as a proxy for ecosystem resilience. My results suggest that forest stands with the lowest resilience to disturbance are those that experienced the compounding effects of climate induced drought stress and high fire severity. These sites were generally located at warmer and drier landscape positions, suggesting they are less resilient to disturbance than sites in cool and moist locations. I conclude that as temperatures continue to warm, the loss of boreal forest resilience to disturbance from fire will vary in association with environmental heterogeneity across the landscape.
      Degree
      Doctor of Philosophy (Ph.D.)
      Department
      Biology
      Program
      Biology
      Supervisor
      Johnstone, Jill F.
      Committee
      Todd, Christopher; Lamb, Eric; Mack, Michelle
      Copyright Date
      May 2015
      URI
      http://hdl.handle.net/10388/ETD-2015-05-2058
      Subject
      boreal forest
      resilience
      fire
      tree-rings
      climate-growth responses
      drought stress
      black spruce
      carbon isotopes
      Collections
      • Graduate Theses and Dissertations
      University of Saskatchewan

      University Library

      The University of Saskatchewan's main campus is situated on Treaty 6 Territory and the Homeland of the Métis.

      © University of Saskatchewan
      Contact Us | Disclaimer | Privacy