Community-level Patterns in Boreal Riparian and Wetland Bird Assemblages

  • Author / Creator
    Morissette, Julienne
  • Canada’s boreal forest is the breeding ground for some 288 species of resident and migratory birds. Approximately 65% of the species that are currently of highest conservation priority in the boreal region are associated with wetlands and riparian areas. Although estimates vary with scale and specific geographic boundaries, wetlands (open water, marshes, fens, bogs and swamps) and other aquatic areas occupy between 20-60% of the boreal landscape. These ecosystems are interspersed with uplands resulting in a heterogeneous landscape hosting a wide variety of transitions, or ecotones, including riparian areas among and within aquatic, wetland and terrestrial systems. Like most ecosystems worldwide, riparian areas within Canada's boreal forests face increasing environmental pressure from the cumulative effects of climate change and unprecedented rates of anthropogenic landscape modification. My objectives were to advance understanding of boreal riparian and wetland-associated bird communities and to evaluate emerging community-level metrics for comparing different habitats and measuring effects of human disturbance. First, I characterized species composition and ecological characteristics of boreal riparian areas associated with open water wetlands which represent a broad spectrum of riparian habitats available to boreal birds. This work demonstrated that riparian zones associated with boreal plain wetlands (shallow lakes and ponds) act as a source of unique bird species and that community dynamics of these ecotones were different from that of upland bird communities. More specifically, I found that bird species composition was more variable in riparian areas than upland sites. I also found that riparian areas supported bird communities that were less specialized in their habitat preferences than those in upland areas. To explore these findings further, I examined whether applying an accepted wetland classification scheme would refine current understanding of habitat associations for birds. My analysis showed that despite some overlap in community composition among wetlands of roughly similar habitat structure (i.e., shrubby wetlands), boreal riparian bird communities were structured differently among a broad suite of wetland classes. This work also showed that wetland communities were distinct from upland communities of similar structure created by forest harvesting. Using indices of ecological function and resilience based on ecological traits of the bird community to compare riparian and upland bird communities, I found riparian bird assemblages possess a different suite of functional traits, higher functional diversity, and greater resilience than the other areas of the landscape I examined. Finally I used, Threshold Indicator Taxa Analysis (TITAN), a technique developed specifically for identifying community-level thresholds (Baker), to explore species-level changes at wetlands along a gradient of agricultural conversion. I compared two spatial scales (local and landscape level) and two geographic regions one in Northeastern Alberta with extensive relatively intact boreal forest immediately to the north and another forested landscape in South western Manitoba embedded in a matrix of agricultural conversion. Community-level changes appeared more abrupt at the landscape than wetland scales but tended to occur over a wide portion of the disturbance gradient, providing only equivocal evidence for community-level thresholds. Species responding positively to agricultural conversion were more typical of open country regions. Species that responded negatively were generally those for which loss of forest cover represented direct loss of habitat. For species common to both regions, specific change points differed but direction of response (+ or -) was consistent. Taken together evidence presented here supports other boreal studies that have shown that for bird communities riparian areas are ecologically unique. They support species rich and subsequently, functionally rich bird communities structured to be more resilient than upland communities. However, even when forest is retained around the periphery of boreal wetlands, conversion to agriculture in the surrounding landscape resulted in species assemblages more typical of open prairie landscapes. Thus my work clearly describes patterns community composition and points to future research necessary to ensure conservation of boreal wetlands and associated bird communities. Greater consideration of ecological traits and community level approaches will compliment species-level work and assist in developing effective conservation and sustainable land use strategies. Data from long term studies of boreal forest bird communities that strategically consider both species- and ecosystem-level changes in boreal bird assemblages in response to environmental gradients over time and including human disturbances will be critical to this effort.

  • Subjects / Keywords
  • Graduation date
    Fall 2014
  • 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.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
  • Specialization
    • Ecology
  • Supervisor / co-supervisor and their department(s)
  • Examining committee members and their departments
    • Dr. Cynthia A Paszkowski (Department of Biological Sciences)
    • Dr. Andre Desrochers (External, Universite Laval)
    • Dr. Keith A. Hobson (Environment Canada)
    • Dr. Lee Foote (Department of Renewable Resources)