Composite Effects of Cutlines and Wildfire Result in Fire Refuges for Plants and Butterflies in Boreal Treed Peatlands

Abstract

The challenge of understanding how composite disturbances affect ecosystems is a central theme of modern ecology. For instance, anthropogenic footprints and wildfire are increasing globally, but how they combine remains poorly understood. Here, we assessed how a disturbance legacy of about 10-m-wide cutlines, cleared for seismic assessments of fossil fuels, affects wildfire dynamics and species assemblages in boreal peatland forests. One year after the Fort McMurray Horse River wildfire of 2016 (Alberta, Canada), we assessed differences in plant and butterfly assemblages across forests and cutlines, from unburned and severely burned peatlands. We hypothesized that, by reducing fire severity, cutlines could support plants and butterflies in the presence of a severe wildfire (the “refuge hypothesis”). Proportion of burned duff was five times higher in burned forests compared to burned cutlines (53% vs. 11%). We found 107 plant and 46 butterfly taxa, with species richness being, respectively, about 1.4 and 1.7 times higher in lines than in forests, independently from wildfire. Models for single species demonstrated different responses to disturbance, including no responses (25% of species), dominant effects of fire or lines (50%), additive effects (10%), and interactive effects (15%). Cutline refuges occurred for 20% of plant and 70% of butterfly species. Multiple lines of evidence suggest that anthropogenic refuges from fire occur in these peatland forests, yet different patterns of responses confirm the complex effects occurring with composite disturbances. Given that cutlines dissect thousands of square kilometers of boreal forests in North America, further studies should investigate their implications on recovery trajectories of these forests’ succession after wildfire.