Disrupted Fire Regimes of the Canadian Montane Cordillera

Keywords: dendrochronology, fire regimes, forest dynamics, human impacts, climate change
Session Type: Virtual Paper
Day: Wednesday
Session Start / End Time: 4/7/2021 01:30 PM (Pacific Time (US & Canada)) - 4/7/2021 02:45 PM (Pacific Time (US & Canada))
Room: Virtual 9

Abstract

Dendroecological reconstructions of historical fire frequency, severity, spatial variability, and extent, corroborated by other lines of evidence, are essential for understanding fire regime drivers and the differences between historical and contemporary regimes. 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. 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 40 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 changes in tree composition and tree density. In absence of surface fires, dense understories of fire-intolerant trees persist, altering forest composition, structure and fuels. We conclude that the exclusion of indigenous cultural burning, followed by 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.