Habitat fragmentation is considered to be a major conservation issue around the world, especially in the context of sensitive forest ecosystems. A growing body of research on ecological corridors has shown they can increase connectivity in fragmented forests, but not all corridors are beneficial. Some types of corridors increase habitat fragmentation and introduce new disturbances with unique effects.
In the boreal forests of western Canada, seismic lines are one of the most prevalent sources of forest fragmentation. Created by the energy industry for oil and gas exploration, seismic lines are both a type of corridor and a type of anthropogenic disturbance, with woody vegetation (i.e. trees) removed to create linear forest openings. They are pervasive throughout the region, especially within Alberta, where densities can reach up to 40 kilometers of seismic lines per square kilometer of forest. With 97% of the oil sands of Alberta too deep to mine conventionally with surface mines, oil extraction instead relies on a network of sub-surface wells, with seismic lines used to estimate the depth of oil deposits for these wells.
Seismic lines vary in size, with two forms being common. “Conventional” lines are 5-10 meters wide and widely spaced in a grid (often 200-500 meters apart). Narrower “low impact” lines are only 1.5-3 meters wide but generally dense, with grid spacing sometimes as close as 50 meters. Conventional seismic lines are now largely historic, with low impact lines being the norm. Both seismic line types can extend for many kilometers, creating large amounts of forest edge despite relatively little (15-20%) overall habitat loss.
The effects of seismic lines were largely unknown for many years and initially not considered a major concern, given that most original habitat remains and they were assumed to recover naturally. However, several research groups have recently begun to uncover the complex responses to seismic line disturbance, including the Applied Conservation Ecology Lab at the University of Alberta, led by Dr. Scott Nielsen.
Seismic lines are associated with many unique ecological responses, among them changes in light and wind patterns. Average light intensity and wind speeds tend to be higher on seismic lines as compared to typical forest interior. These abiotic changes can potentially change the composition of local plant communities, as wind-dispersed seeds tend to travel much farther along seismic lines.
Seismic lines also affect the health and reproduction of important understory shrubs. For example, the velvet leaf blueberry (Vaccinium myrtilloides) tends to grow taller and have a higher reproductive success on seismic lines, a potential positive response to disturbance given the cultural and ecological importance of this shrub.
Seismic lines have been shown to affect the movement, abundance, and diversity of local invertebrates, including butterflies. Evidence shows that narrow, low impact lines support similar butterfly abundance and diversity as control forests, suggesting that recent shifts to narrower lines are beneficial to maintaining forest conditions.
In addition, recent projects have shown that fire has the potential to be an effective restoration tool for forests fragmented by seismic lines. Fire removes biomass and exposes mineral soils, which allows shade-intolerant species to flourish and recover natural forest characteristics.
Overall, seismic lines are a unique type of anthropogenic corridor that fragment forest landscapes in a way that is underappreciated. More research is needed to inform the management and restoration of these disturbances to minimize their long-term effects on the boreal forest. Current efforts attempt to better understand how seismic lines interact with other important forest processes, such as pollination, invasion, and recovery strategies. Recent advances in technology also provide potential solutions for minimizing forest fragmentation, by allowing for seismic assessments that do not disturb vegetation and thus do not require open corridors.
Dawe CA, Filicetti AT and Nielsen SE. 2017. Effects of linear disturbances and fire severity on velvet leaf blueberry abundance, vigor, and berry production in recently burned jack pine forests. Forests 8(10): 398.
Filicetti AT and Nielsen SE. 2018. Fire and forest recovery on seismic lines in sandy upland jack pine (Pinus banksiana) forests. Forest Ecology and Management 421: 32-9.
Riva F, Acorn JH and Nielsen SE. 2018. Narrow anthropogenic corridors direct the movement of a generalist boreal butterfly. Biology Letters 14: 20170770.
Riva F, Acorn JH and Nielsen SE. 2018. Localized disturbances from oil sands developments increase butterfly diversity and abundance in Alberta’s boreal forests. Biological Conservation 217: 173-80.
Roberts D, Ciuti S, Barber QE, Willier C and Nielsen SE. 2018. Accelerated seed dispersal along linear disturbances in the Canadian oil sands region. Scientific Reports 8: 4828.
Stern ER, Riva F and Nielsen, S.E. 2018. Effects of narrow linear disturbances on light and wind patterns in fragmented boreal forests in northeastern Alberta. Forests 9(8): 486.