Seismic line width and wildfire promote ring growth in regenerating black spruce

Across western Canada, networks of narrow forest clearings used to delineate underground oil and gas deposits lead to the dissection and fragmentation of forested boreal peatlands. These ‘seismic lines’ compress peatland surfaces, delaying tree regeneration. Wildfire is a dominant driver of succession and subsequently interacts with seismic lines. In forested boreal peatlands, wildfire can promote regeneration, but it can also compound the effects if on seismic lines. While responses in tree density and height on seismic lines have been well studied, radial growth has not. To address this gap, we examined 139 cross-sections of regenerating black spruce and tamarack on seismic lines in forested peatlands to summarize radial growth with and without recent wildfire in the last 25 years. We then elucidate which site and disturbance characteristics most influenced the radial growth of black spruce. Specifically, we compared 18 a priori candidate models of different disturbance and site characteristics, both additive and interactive, hypothesized to influence black spruce growth. The most supported model included the additive effects of wildfire and width of seismic line. Mean annual ring width from 2013 to 2017 in black spruce increased by 12 % (95 % CI 0, 24; p = 0.043) for every 1 m increase in seismic line width and increased by 42 % (95 % CI 3, 96; p = 0.031) if lines had recently burned. Our results demonstrate that radial growth of black spruce increases on recently burned, wider seismic lines in forested peatlands. Restoration of seismic lines will require consideration of multiple growth responses to disturbances especially wildfires which are burning more frequently in western Canada. • Additive effects of wildfire and seismic line width promote radial growth in forested peatlands. • Mean annual ring width in black spruce increased 12 % for every meter increase in seismic line width. • Mean annual ring width in black spruce increased 42 % after a recent wildfire. • Seismic line restoration planning should consider the effects of wildfires on hastening recovery.