Jennifer L. Beverly

Modelling the probability of sustained flaming: predictive value of fire weather index components compared with observations of site weather and fuel moisture conditions

We investigated the likelihood that short-duration sustained flaming would develop in forest ground fuels that had direct contact with a small and short-lived flame source. Data from 1027 small-scale experimental test fires conducted in field trials at six sites in British Columbia and the North-West Territories between 1958 and 1961 were used to develop logistic regression models for ten fuel categories that represent unique combinations of forest cover, ground fuel type, and in some cases, season. Separate models were developed using two subsets of independent variables: (1) weather variables and fuel moisture measurements taken at the site of the test fire; and (2) Canadian Fire Weather Index (FWI) system components calculated from weather observations recorded at a nearby station. Results indicated that models developed with FWI system components were as effective as models developed with site variables at predicting the probability of short-duration sustained flaming in most fuel categories. FWI system components were not useful for predicting sustained flaming in spring grass fuels and had limited usefulness for modelling the probability of sustained flaming in aspen leaf ground fuels during summer conditions. For all other fuel categories, FWI system components were highly effective substitutes for site variables for modelling the probability of sustained flaming.

Stand-specific litter moisture content calibrations for the Canadian fine fuel moisture code

A large dataset of litter moisture measurements collected at several sites across Canada by the Canadian Forest Service over the period from 1939 to 1961 is analysed. The stands in which sampling was carried out were described by three main variables: forest type (pine, spruce, Douglas fir, mixedwood and deciduous), season (spring, summer and fall), and stand density (light, moderate and dense). All three variables were found to have a significant influence on the relationship between the Canadian Forest Fire Weather Index System’s Fine Fuel Moisture Code (FFMC) and surface litter moisture. Moisture in the upper duff layer was also found to have a significant influence on the relationship between FFMC and litter moisture content, with a wetter duff layer leading to moister surface conditions than would be indicated by the FFMC value. A model for litter moisture is developed, which provides a method of adjusting the standard FFMC value for the influences of forest type, stand density, season and duff moisture content.

Assessing the exposure of the built environment to potential ignition sources generated from vegetative fuel

We assessed the exposure of the built environment to potential ignition sources generated from vegetative fuel for four communities in the province of Alberta, Canada. Ignition processes generated by burning vegetation that were included in the analysis were radiant heat, short-range spotting, and longer-range spotting. Results were used to map the boundaries of the wildland–urban interface and to delineate zones within each community that identify the degree to which these areas represent potential wildfire entry-points into the wildland–urban interface. The assessment method can be used to set priorities for mitigation activities; compare conditions within and between communities and over time; and identify priority areas for time- and resource-intensive site assessments that are often completed for individual structures located in the wildland–urban interface. We compared results among the four case-study communities and demonstrated an application of the approach for evaluating community fuel treatment plans. Factors that influenced the exposure of the built environment to potential ignition sources differed among the communities, which suggested the need for community-specific mitigation strategies. Spatial patterns of areas with elevated ignition exposure reflected not only the amount of ignition-producing vegetation around the built environment, but also the size and arrangement of fuel patches in relation to the unique morphology of the community and the occurrence of occluded interface zones.

Time since prior wildfire affects subsequent fire containment in black spruce

In black spruce forests characterised by high-intensity crown fires, early detection and containment of fires while they are small is crucial for averting progression to fire intensities that exceed suppression capabilities. Fire behaviour conditions encountered during initial attack operations are a key determinant of containment success. Conditions will be controlled in part by stand structural characteristics that can be expected to vary as a fire-origin black spruce (Picea mariana (Mill.) B.S.P.) stand ages with increasing time-since-fire. In this study, the influence of time-since-fire on containment outcomes is assessed to explore whether or not prior wildfire exerts a negative feedback on subsequent fires in these ecosystems. Logistic regression analysis using point and polygon fire data for the province of Alberta, Canada, indicated the probability of a containment failure in black spruce increases with time-elapsed since the last fire. Other positive explanatory variables included the size of the fire at the initiation of firefighting and a relative rating of the expected rate of fire spread, the Initial Spread Index (ISI) of the Canadian Forest Fire Weather Index System. Legacy wildfires had a protective effect. When firefighting is initiated at fire sizes ≤1ha, the probability of a containment failure is low during the initial 20–45 years of post-fire stand development, except under the most extreme fire weather conditions.

Characterizing Historical Variability in Boreal Forest Fire Frequency: Implications for Fire and Forest Management

Fire management policies emerged as a means of controlling widespread social, economic and ecological impacts of fire. However, it is now recognized that complete fire exclusion is ecologically and economically undesirable, and an operational impossibility. Alternative fire management strategies have been most progressive in wilderness parks, with management plans aimed at perpetuating historical variability associated with natural fire processes. This paper briefly reviews historical variability concepts and the fire history model as a basis for natural fire management in protected areas. Time-since-fire forest age distribution data for Wabakimi Provincial Park, Ontario, Canada, is used to characterize historical variability in boreal forest fire frequency. The implications of this historical variability for future forest and fire management are discussed.