Ecological - First Order
Fire Intensity / Burn Severity
With longer and more severe fire seasons predicted, the incidence and extent of fires are expected to increase in western North America. As more area is burned, past wildfires may influence the spread and burn severity of subsequent fires, with implications for ecosystem resilience and fire management. We examined how previous burn severity, topography, vegetation, and weather influenced burn severity on four wildfires, two in Idaho, one in Washington, and one in British Columbia. These were large fire events, together burning 330,000 ha and cost $165 million USD in fire suppression expenditures. Collectively, these four study fires reburned over 50,000 ha previously burned between 1984 and 2006. We used sequential autoregression to analyze how past fires, topography, vegetation, and weather influenced burn severity. We found that areas burned in the last three decades, at any severity, had significantly lower severity in the subsequent fire. Final models included maximum temperature, vegetation cover type, slope, and elevation as common predictors. Across all study fires and burning conditions within them, burn severity was reduced in previously burned areas, suggesting that burned landscapes mitigate subsequent fire effects even with the extreme fire weather under which these fires burned.