Projecting boreal bird responses to climate change considering uncertainty, refugia, vegetation lags, and post-glaciation history

  • Author / Creator
    Stralberg, Diana
  • Often referred to as North America’s bird nursery, the boreal forest biome provides a productive environment for breeding birds, supporting high species diversity and bird numbers. These birds are likely to shift their distributions northward in response to rapid climate change over the next century, resulting in population- and community-level changes. To anticipate the pattern and extent of such changes, and to inform climate-change adaptation and conservation planning, species distribution models (SDMs) are often used to describe and map species’ climatic niches through time. SDMs provide invaluable insights into climatic suitability patterns and potential distributional responses, but they are most useful when assumptions are acknowledged and the resulting limitations are addressed. Each chapter of my thesis focuses on understanding and addressing one of four major limitations of SDMs: (1) model uncertainty in current and future projections, (2) time lags in ecosystem responses to climate change, (3) the static nature of correlative models, and (4) the influence of historical biogeography in determining current distributions. In my first chapter, using a continental-scale avian dataset compiled by the Boreal Avian Modelling project, I developed models to project climate-induced changes in the distribution and relative abundance of 80 boreal-breeding passerine species. For such projections to be useful, however, the magnitude of change must be understood relative to the magnitude of uncertainty in model predictions. I found that the mean signal-to-noise ratio across species increased over time to 2.87 by the end of the 21st century, with the signal greater than the noise for 88% of species. I also found that, among sources of uncertainty evaluated, the choice of climate model was most important for 66% of species, sampling error for 29% of species, and variable selection for 5% of species. The range of uncertainty exhibited across species and geographic regions suggests a basis for differential quantitative weightings in assessments of species vulnerability and spatial conservation priorities under climate change. Many species and ecosystems will likely be unable to keep pace with rapid climate change projected for the 21st century, however. In my second chapter, I evaluated an underexplored dimension of the mismatch between climate and biota: limitations to forest growth and succession affecting habitat suitability. I found dramatic reductions in suitable habitat for many species over the next century when vegetation lags were considered. I used these results to identify conservative and efficient boreal conservation priorities anchored around climatic macrorefugia that are robust to century-long climate change and complement the current protected areas network. Vegetation change may also be delayed in the absence of disturbance catalysts. In the western boreal region, a combined increase in wildfires and human activities may aid these transitions, also resulting in a younger forest. In my third chapter, I developed a hybrid modelling approach based on topo-edaphically constrained projections of climate-driven vegetation change potential, coupled with weather- and fuel-based simulations of future wildfires, and projections of large-scale industrial development activities, to better understand factors influencing decadal-scale upland vegetation change. I simulated scenarios of change in forest composition and structure over the next century, conservatively concluding that at least one-third of Alberta’s upland mixedwood and conifer forest is likely to be replaced by deciduous woodland and grassland by 2090. During this timeframe, the rate of increase in fire probability diminished, suggesting a negative feedback process by which a warmer climate and more extensive near-term fires leads to an increase in deciduous forest that in turn, due to its relatively low flammability, leads to a long-term reduction in area burned. Finally, boreal species’ projected range shifts could be impeded by the northwestern cordillera, which spans from boreal Alaska to the rest of the North American boreal region, and may have inhibited the expansion of many species into climatically suitable habitat after the last glacial maximum (LGM). Using paleoclimate simulations for the past 20,000 years, I analyzed the relative importance of migratory and life-history characteristics vs. current and historical climatic suitability on the distributions of North American boreal-breeding species. The high relative importance of climatic suitability within the northwestern cordilleran region suggests a capacity for several species to disperse into Alaska once climatic connectivity is achieved in the future, which is supported by recently recorded signs of breeding activity.

  • Subjects / Keywords
  • Graduation date
    Spring 2016
  • 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.