Are landbirds in the Athabasca Oil Sands Area affected by the cumulative effect of multiple stressors? Can we simply add together the effect of stressors or is the effect even greater when stressors are multiplied?
A project initiated by Dr. C. Lisa Mahon, Canadian Wildlife Service, Environment and Climate Change Canada, and Dr. Gillian Holloway, ecological consultant, set out to answer these questions. Working in collaboration with Dr. Erin Bayne, University of Alberta, and Dr. Judith Toms, Canadian Wildlife Service, this study was funded by the Oil Sands Monitoring (OSM) Program. Published recently in the journal Ecological Applications, the resulting research article is titled: “Additive and interactive cumulative effects on boreal landbirds: winners and losers in a multi-stressor landscape.”
Major stressors to landbirds in the Athabasca Oil Sands Area result from resource development activities including energy exploration (seismic lines, exploration wells) and extraction (pipelines, production wells and industrial facilities), forest harvesting (harvest units and roads), and infrastructure construction (roads, railways and power lines). Typically, researchers assume that the cumulative effect of multiple stressors can be simply added together (additive effect). Work in marine systems suggests that the cumulative effect of multiple stressors can be multiplied together (interactive effect). This results in complex effects that could be larger than additive effects. It makes understanding and managing the impact of stressors more difficult.
The study focused on examining the effects of linear stressors (seismic lines, pipelines, power lines and roads), energy stressors (wells), and forestry stressors (harvest units) on 27 species of boreal landbirds.
What did the researchers find?
ECCC scientists and staff surveyed boreal landbirds at more than 2700 sample sites across the 9.3 million hectare Athabasca Oil Sands Area in Alberta to examine the effects of linear stressors, energy stressors, and forestry stressors. The authors found that resource development stressors affected abundance for 20 of the 27 landbird species considered (74%) and that complex interactive effects among stressors affected abundance for 11 of the 27 landbird species. In areas with many stressors, researchers found fewer conifer-associated species (e.g. Bay-breasted Warbler, Boreal Chickadee, Canada Jay, and Red-breasted Nuthatch) and more deciduous-associated species like Black-capped Chickadee, Red-eyed Vireo, and Rose-breasted Grosbeak. This is most likely due to the deciduous vegetation that moves in after a disturbance (e.g. sun-loving shrubs and alder, willow, and poplar tree species).
The authors also found evidence for a 15% change in the landbird community between the current study area where disturbance is 8.4% and the same study area with no disturbance. Many conifer bird species are specialists within the western boreal landbird community meaning that they use only a narrow range of resources or habitat conditions. Broader monitoring programs indicate that several conifer specialists are declining across the boreal forest. Current resource development in western boreal forests will continue to replace older mixedwood and conifer forests with young deciduous forests. This is expected to decrease the abundance of conifer-associated bird species (losers) and increase deciduous-associated bird species (winners).
Mahon states “our results indicate that cumulative effects of resource development are causing a replacement of specialist species by generalist species and the magnitude of these effects are greater than the simple sum of the areas affected by individual stressors. How these complex small-scale stressor effects will be affected by large-scale disturbance effects like climate change is unknown.”
What’s Next?
The authors note that based on the results, they would like to see regional land use plans and environmental assessments (EA) include interactions among small and large-scale stressors. The goal is to be able to better predict the cumulative effects of multiple resource industries.
The paper emphasizes that the study’s results are preliminary and that work on this area will continue. The researchers note it is premature to provide prescriptive advice to policymakers at this stage.
“Further studies will be needed before we can fully account for this complexity in land use planning and environmental assessments” the study states.
This research was funded by the Oil Sands Monitoring (OSM) Program.