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Historical fire regime of the Darkwoods : quantifying the past to plan for the future Greene, Gregory Allen


This study quantifies the fire history of the Darkwoods; a 55,000 ha property in the South Selkirk Natural Area of southeastern British Columbia, owned and managed by the Nature Conservancy of Canada. Fire scar and tree cohort chronologies from 45 plots, extending from the years 1406 – 2010, were used to determine the temporal and spatial variability of historic fires in ~4,000 ha of the southeastern-most watershed of the property, and to assess the accuracy of provincial Natural Disturbance Type (NDT) classes for the study area. In light of a mixed-severity fire regime, new and novel methods of historic fire mapping using Inverse Distance Weighting methods in a GIS were also analyzed. Using logistic regression, the spatial variation of fires at the tree- and plot-levels differed greatest by elevation, but fires at the tree-level also varied by slope steepness and slope aspect. Anthropogenic influences on the occurrence of fire over time were also evident, but only after 1945, when the occurrence of fire dropped significantly likely due to the introduction of modern methods of fire suppression in the 1940s. Results indicate a mixed-severity fire regime for the study area, and the presence of numerous fire scars in mid- and high- elevation plots, in conjunction with mean fire return intervals less than 100 years, provide evidence that conflicts with provincial NDT designations. Including high-elevation stand ages, determined from increment cores, provided evidence of the absence of fire and helped refine estimates of fire boundaries, particularly in and around areas experiencing mixed- and high-severity fires. Spatial Mean Fire Intervals were longer than those calculated at the tree-, plot- and watershed-levels, reflecting the degree to which a mix of high-severity, stand-replacing fires, with low- and moderate-severity, stand-maintaining fires, can lengthen mean return intervals across a mixed-fire landscape.

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