Edge influence from linear disturbances and recovery of understory communities in boreal forests

  • Author / Creator
    Echiverri, Laureen F. I.
  • Forest fragmentation is one of the leading causes of global biodiversity loss and is only expected to increase with the continued rise of anthropogenic disturbances. An important environmental consequence of fragmentation is edge influence—the set of ecological changes which occur at the interface of a forest and the adjacent non-forested patch. In the boreal forests of western Canada, seismic lines are one of the primary drivers of forest fragmentation. Seismic lines are narrow, linear disturbances used to locate fossil fuel reserves. Seismic lines are slow to recover and tend to persist in the landscape, contributing to their long-term widespread presence. To facilitate seismic line recovery, mounding is currently being applied to create micro-sites for tree establishment. In this thesis, I examine the edge influence of seismic lines on understory communities and assess the impacts of restoration efforts. Specifically, my objectives are to: 1) assess how edge influence from multiple seismic lines interacts and affects the understory communities of treed fens, 2) explore the mechanisms driving edge influence on the understory vegetation by examining the population- and individual-level performance of an herbaceous annual, Melampyrum lineare, in xeric, pine-dominated stands, and 3) assess the impact of mounding on understory community recovery in treed fens. To address these objectives, I sampled seismic lines and the adjacent forest in treed fens and pine-dominated stands in northeastern Alberta.
    Despite their narrow nature, I found that seismic lines had a significant edge influence on the understory vegetation in treed peatlands. In addition, I found evidence of edge interaction when multiple seismic lines were in proximity. For example, in poor fens, multiple seismic lines had a strengthening edge interaction: single seismic lines did not have an edge influence on vegetation, while multiple seismic lines led to higher tree density in the adjacent fen. In xeric, pine-dominated stands, I found a sealing effect at the edges of wider and older seismic lines, with woody vegetation increasing in abundance at the edge. In addition, I found that the population-level performance of Melampyrum lineare was shaped by the presence of seismic lines—with higher population density and seed production on the seismic lines. In contrast, at the individual-level, performance was primarily shaped by the vegetation surrounding each individual. Finally, while seismic lines left to recover naturally showed promising results, with the re-establishment of a peat-accumulating understory community, I found that attempts to re-create micro-sites for tree establishment on seismic lines only set back the recovery of understory communities in treed peatlands. Overall, these results show the complex impacts of fragmentation and the importance of evaluating the effects of restoration techniques, prior to their widespread use. Considering these results, I recommend 1) utilizing recent technology to prevent or minimize any additional creation of conventional and/or low impact seismic lines and 2) minimizing or preventing any additional disturbance on existing seismic lines.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.