Managing Fire Mosaics for Biodiversity

The Canadian boreal forest is the largest and most intact forest remaining on the planet. Since the last glacial period, it has been shaped by recurrent and extensive stand-replacing wildfires that have given rise to a mosaic of habitat patches varying in age, extent, and wildfire history. Recent human activities (e.g., fire suppression, climate warming) that influence important top-down (weather) and bottom-up (availability and distribution of fuel) controls over wildfire activity have resulted in recurrent record-breaking wildfire seasons in Canada. Nationally, these changes are characterized by longer fire seasons, more days suitable for fire spread, and increases in both the annual area burned and the number of large wildfires (>200 ha). These landscape-level changes combined with anticipated increases in future wildfire activity have the potential to reduce biodiversity by reducing stand-age heterogeneity of the boreal patch mosaic. This thesis explores the link between spatiotemporal elements of wildfire and biodiversity in the Canadian boreal forest and the suitability of different theoretical frameworks for guiding conservation planning in the face of global change. It also explores the ecology of fire-dependent insects, highlighting important components of boreal biodiversity and instances of co-evolution with wildfire.\nUsing a collection of 42 lake islands spanning gradients in island area (1-350.4 ha), isolation (0.1-7.9 km from mainland), and fire history (1-231+ years since fire), I show that wildfire-mediated habitat heterogeneity (i.e., pyrodiversity) better explains species richness and beta diversity of beetles, plants, and birds than island area, isolation, and habitat amount. My findings support the pyrodiversity-biodiversity hypothesis and the idea that boreal biodiversity is fundamentally linked to the spatiotemporal components of the patch mosaic. I conclude that maintaining even small, isolated patches of old growth forest on the mainland would conserve important components of temporal pyrodiversity and that the natural fire refugia effects of large lakes in the region could be utilized for this purpose. \nThe recently burnt islands in my study also supported unique fire-adapted insect species not detected on any of the other islands (5 to 231 years since fire). These insects are part of a larger community of pyrophilic insects (50+ species), mainly beetles and flies, that are adapted for exploiting reproductive advantages in the post-burn environment. Through rearing studies of Sericoda spp. (Coleoptera: Carabidae), I demonstrate that background rates of egg predation in forest soils are high and that these costs may be reduced by ovipositing in soils sterilized by the extreme heat of wildfires. Finally, I document pyrophilic dispersal behaviour during an extreme weather event that ignited 17 wildfires in my study region and show that the pyrophilic ground beetle, Sericoda obsoleta, is capable of dispersing 50+ km under favourable wind conditions. I conclude that successive generations of pyrophilic insects are likely capable of dispersing between wildfires and hypothesize that convective updrafts during storms and wildfires may transport these insects very far from their birthing grounds.

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