Composite Effects of Cutlines and Wildfire Result in Fire Refuges for Plants and Butterflies in Boreal Treed Peatlands
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.
Keywordsboreal forest disturbance in situ oil sands habitat fragmentation seismic lines dispersal linked and compound effects interactive effects synergy
We thank COSIA (CRDPJ 498955), Alberta Innovates—Energy and Environmental Solutions (ABIEES 2070), Alberta Agriculture and Forestry (15GRFFM12), NSERC-CRD, LRIGS via the NSERC-CREATE program (CRD 498955-16, CREATE 397892), Alberta Conservation Association via the ACA Grants in Biodiversity (RES0034641), and Xerces Society via the Joan Mosenthal DeWind Award (RES0036460) for supporting this research. We also thank Fionnuala Carrol and Marcel Schneider for participating in the project as summer undergraduate assistants, Angelo Filicetti, Francis K. C. Hui, Nick M. Haddad, Felix A. H. Sperling, and Hans Van Dyck for insightful comments on the manuscript, and Dr. Turner, Dr. Seidl and two anonymous reviewers for insightful comments on the manuscript
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