Responses in butterflies to loss and fragmentation of boreal forests from in situ oil sands

Federico Riva
2019
Anthropogenic loss and fragmentation of habitat are a threat to biodiversity, while increasing demands for energy have made the provision of fossil fuels an important source of disturbance to habitats around the globe. In Alberta, Canada, the extraction of a 142,000 km 2 oil sands reserve is causing one of the largest examples of habitat fragmentation worldwide. Approximately 97% of Alberta's reserves are located underground, and thus are accessible only using subsurface wells, a practice
more » ... s, a practice defined as "in situ" extraction. In situ extraction of oil sands results in little overall loss of boreal forest habitat, usually limited to less than 20% of forest cover, but it causes high levels of forest fragmentation, with up to 50 km of linear features per km 2 of forest. Although in situ oil sands affect vast areas of the boreal biome, and despite many important services provided by insects in boreal ecosystems, virtually no information is available on responses in insect taxa. In this thesis, I assessed how butterflies responded to the disturbance footprint associated with in situ oil sands in the boreal forests of northeastern Alberta, Canada, with a specific focus on the effects of seismic lines. First, I assessed changes in butterfly assemblages as a function of different disturbance types and measures of landscape fragmentation. I found consistent, positive effects of in situ disturbances on butterfly diversity and abundance, and small effects of landscape in moderating the local composition of butterfly assemblages. Notably, while even "conventional" seismic lines substantially increased butterfly diversity and abundance, "lowimpact" seismic lines were successful in mitigating this response. Second, I used experimental releases of arctic fritillaries (Boloria chariclea) to assess if corridors affect the movement of a habitat generalist butterfly. Both low-impact and conventional lines equally conditioned the movement of arctic fritillaries, directing butterflies toward the line direction. Effects were iii independent from forest and corridor characteristics, as well as the sex of the butterflies. Third, I studied how cranberry blue butterflies (Agriades optilete) responded to in situ oil sands disturbances and wildfires. As with most other butterfly species, I observed more cranberry blues in seismic lines. Yet, cranberry blues avoided well pads and were rare in burned forests, suggesting sensitivity to forest disturbance of this species. Last, I examined how the presence of seismic lines in burned forests conditioned plant and butterfly populations one year after the Fort McMurray Horse River wildfire (2016). By reducing wildfire severity, seismic lines retained the initially more diverse plant and butterfly assemblages, even in severely burned forests, suggesting that these anthropogenic linear features can act as "refugia" for species negatively affected by wildfire. Overall, this work demonstrated strong responses in butterflies to forest disturbances associated with in situ oil sands, suggesting that substantial effects could occur for numerous invertebrate taxa that inhabit these forests. While most boreal butterflies depend on early seral stages of the forest succession, and thus benefit from the patches of early seral forest associated with in situ disturbances, organisms that depend on mature forest stages may suffer from negative effects due to loss and fragmentation of mature forest habitat. Mitigating the effects of the widespread disturbance footprint associated with in situ oil sands remains a priority, and reducing line width to less than 5 m confirmed an effective mitigation practice not only for vertebrates, but also for butterflies. iv
doi:10.7939/r3-6078-p790 fatcat:k4sk3kr6v5ecpi6eml5wvm5yxu