Green islands in a sea of fire: the role of fire refugia in the forests of Alberta

Abstract

Alberta wildfires vary greatly in severity, resulting in a mosaic of burnt, partially burnt, and unburnt forest. These unburnt patches (refugia) within the fire perimeter are critical for the survival of organisms during the fire and the regeneration process. We examined the literature to identify how the fire regimes and landscape features found in Alberta affect the creation and persistence of refugia, the role of refugia for the flora and fauna of Alberta, how climate change is likely to affect refugia, how humans may alter the creation and effectiveness of refugia, and management implications moving forward. Refugia can vary in scale from small areas of unburnt soil or boulders (centimetres to a few metres), to large stands of unburnt trees (many hectares) with different taxa using these refugia across all the spatial scales. Species reliant on habitat connectivity or old growth forest also benefit from refugia as they can use them as stepping-stones between intact habitats or as a lifeboat to recolonize from. The factors influencing what areas remain unburnt are complex and poorly understood but are likely tied to topography, aspect, proximity to waterbodies, weather changes (precipitation and wind direction), time of day during burning, and vegetation type. Areas with the right combination of topography, aspect, and proximity to water have cooler microclimates and higher moisture than the surrounding areas and may remain unburnt throughout multiple fire events, making them persistent refugia. Other areas may remain unburnt by a chance result of weather changes or having the fire pass through at night, making them random refugia. Many of the features that make persistent refugia unlikely to burn (cooler microclimate and higher moisture) will also buffer the effects of climate change. As a result, it is essential we manage the landscape in such a way as to protect areas that act as persistent refugia from industrial activities. In addition, we must restore fire in the landscape to maintain the mosaic of forest caused by mixed-severity fire, especially in the face of climate change, which is projected to increase the severity and frequency of wildfires in Alberta.