Wildfire is a wicked problem. Although wildfire is a vital natural disturbance in forests worldwide, recent large and costly fires have raised urgent questions about fire regime drivers and the differences between historical and contemporary regimes. Dendroecological reconstructions of historical fire frequency, severity, spatial variability, and extent, corroborated by other lines of evidence, are essential in addressing these questions. Existing methods can infer the frequency and severity of individual fires and stand-level fire regimes. Novel research designs combining evidence of stand-level fire severity with fire extent are used to reconstruct spatial variability in historical fire regimes and to quantify the relative abundance of fire severity classes across landscapes. Here we show how new approaches build on traditional analyses of fire scars and forest age structures provide a deeper understanding of the role of wildfire in montane forests of British Columbia and the Canadian Rocky Mountain National Parks.
Results/Conclusions
Our fire history reconstructions show that historical fire regimes in montane forests included a mix of frequent lower-severity surface fires and periodic higher-severity crown fires. In many montane forests, lower-severity fires historically burned and scarred trees every 10 to 60 years for several centuries up to the 1900s. Despite the historical frequency of fires and recent periods of suitable climate, these forests last burned causing fire scars 40 to 160 years ago – providing strong evidence of the effects of altered fire regimes during the 20th century. The lack of recent fires is reflected in forest composition and tree density. In absence of surface fires, dense understories of fire-intolerant trees persist, altering forest composition, structure and fuels. We conclude the cumulative effects of land-use change, early 19th century logging, even-aged silviculture, and fire suppression during the 20th century have altered the fire regimes and reduced the resilience of Canada’s montane forests. Our findings illustrate the importance of ecosystem-specific research to guide management aiming to safeguard human, cultural and biological values in fire-prone forests and enhance forest resilience to the cumulative effects of global environmental change. Dendroecological reconstructions, combined with corroborating evidence, are key for resolving the wicked problem of wildfire.