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Technical Thematic Report No. 6. - Trends in large fires in Canada, 1959 to 2007

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Trends in large fires in Canada, 1959-2007

Cover page of the publication: Trends in large fires in Canada, 1959­2007

C.C. Krezek-Hanes,Footnote[1] F. Ahern,Footnote[2] A. CantinFootnote[1] and M.D. FlanniganFootnote[1]

Canadian Biodiversity: Ecosystem Status and Trends 2010
Technical Thematic Report No. 6
Published by the Canadian Councils of Resource Ministers

Library and Archives Canada Cataloguing in Publication

Trends in large fires in Canada, 1959-2007.

Issued also in French under title:
Tendances des grands incendies de forêts au Canada, de 1959 à 2007.
Electronic monograph in PDF format.
ISBN 978-1-100-18917-8
Cat. no.: En14-43/6-2011E-PDF

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This report should be cited as:
Krezek-Hanes, C.C., Ahern, F., Cantin, A. and Flannigan, M.D. 2011. Trends in large fires in Canada, 1959-2007. Canadian Biodiversity: Ecosystem Status and Trends 2010, Technical Thematic Report No. 6. Canadian Councils of Resource Ministers. Ottawa, ON. v + 48 p.

© Her Majesty the Queen in Right of Canada, 2011
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Footnote 1

Canadian Forest Service, Natural Resources Canada

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Footnote 2

TerreVista Earth Imaging, Cormac, Ontario

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The Canadian Councils of Resource Ministers developed a Biodiversity Outcomes FrameworkFootnote1 in 2006 to focus conservation and restoration actions under the Canadian Biodiversity Strategy.Footnote2 Canadian Biodiversity: Ecosystem Status and Trends 2010Footnote3 was a first report under this framework. It assesses progress towards the framework’s goal of “Healthy and Diverse Ecosystems” and the two desired conservation outcomes: i) productive, resilient, diverse ecosystems with the capacity to recover and adapt; and ii) damaged ecosystems restored.

The 22 recurring key findings that are presented in Canadian Biodiversity: Ecosystem Status and Trends 2010 emerged from synthesis and analysis of technical reports prepared as part of this project. Over 500 experts participated in the writing and review of these foundation documents. This report, Trends in large fires in Canada, 1959-2007, is one of several reports prepared on the status and trends of national cross-cutting themes. It has been prepared and reviewed by experts in the field of study and reflects the views of its authors. Since the analysis for this report was completed in 2009, trends for total area burned in Canada by decade were calculated including data up to 2010. Results can be found on page 96 of Canadian Biodiversity: Ecosystem Status and Trends 2010 (Federal, Provincial and Territorial Governments of Canada, 2010).

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We thank the reviewers of this report.

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Ecological Classification System – Ecozones+

A slightly modified version of the Terrestrial Ecozones of Canada, described in the National Ecological Framework for CanadaFootnote4, provided the ecosystem-based units for all reports related to this project. Modifications from the original framework include: adjustments to terrestrial boundaries to reflect improvements from ground-truthing exercises; the combination of three Arctic ecozones into one; the use of two ecoprovinces – Western Interior Basin and Newfoundland Boreal; the addition of nine marine ecosystem-based units; and, the addition of the Great Lakes as a unit. This modified classification system is referred to as “ecozones+ throughout these reports to avoid confusion with the more familiar “ecozones” of the original frameworkFootnote5.

Ecological classification framework for the Ecosystem Status and Trends Report for Canada.

Long Description for Ecosystem Status and Trends Report for Canada

This map of Canada shows the ecological classification framework for the Ecosystem Status and Trends Report, named "ecozones+". This map shows the distribution of 15 terrestrial ecozones+, two large lake ecozones+, and nine marine ecozones+.

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Fire is an important disturbance in the forest ecosystems of Canada. On average, 18,471 km² of forest burn annually, 92% of which burns within the boreal forest. Due to the long history of fire in the boreal forest, many boreal tree species have evolved to rely on fire to perform important ecological functions including: nutrient cycling, influencing species composition and age structure, maintaining productivity and diversity of habitats, and regulating insects and disease (Weber and Flannigan, 1997; McCullough et al., 1998; Volney and Hirsch, 2005; Parker et al., 2006; Soja et al., 2007). The boreal forests of Canada are primarily contained within the Taiga Plains, Taiga Shield, Taiga Cordillera, Boreal Plains, Boreal Shield, Newfoundland Boreal, Boreal Cordillera, and Hudson Plains ecozones+. From an ecological standpoint fires can be an essential driver of ecosystem processes in these and other ecozones+.

Characteristics of the fire regime (fire frequency, size, intensity, type, seasonality, and severity) have been shown to influence forest ecology and species composition (Vaillancourt et al., 2009). Areas that experience frequent fires select for species that take advantage of shorter life cycles, for example trembling aspen (Populus tremuloides Michx) (de Groot et al., 2003), compared to species like balsam fir (Abies balsamea (L.) Mill.), which are found in areas with less frequent fire occurrence, such as the Atlantic Maritime (Weber and Flannigan, 1997).

Fire size affects landscape patchiness by influencing regeneration distances. Areas where larger fires typically occur, such as the Boreal Shield, typically contain species that can spread their seeds over large distances, for example birch (Betula papyrifera Marsh) (de Groot et al., 2003) or that have an aerial seedbank, such as Pinus banksiana or Picea mariana (Chabot et al., 2009).

Fire intensity is a measure of the energy released during a fire. Intensity depends on fuel loads, topography, and weather, and can also be affected by previous disturbances. Some tree species are strongly affected by fire intensity, for example red pine (Pinus resinosa Aiton) (Flannigan and Bergeron, 1998). Although red pines are dependent on fire to promote regeneration by opening the canopy and reducing competition; they are limited by intense crown fires that cause mortality. Mature pines can survive moderately intense surface fires allowing them to persist after fire and act as a seed source for the next generation (Flannigan and Bergeron, 1998). Another example of the ecological effects of intensity is from species such as Jack pine (Pinus banksiana Lamb) and lodgepole pine (Pinus contorta Dougl.), which store seeds in their canopy requiring moderately intense crown fires to occur at an intermediate cycle (reproductive age is 20 to 25 years) (Amiro et al., 2004; Burton et al., 2008) to disperse seeds (Weber and Flannigan, 1997; Flannigan et al., 2000; Gauthier et al., 2009). The seeds of these species are stored in serotinous cones that require high temperatures to open and release the seeds for dispersal (Beaufait, 1960; Gauthier et al., 1996).

Fire intensity can also be related to fire type. There are three types of forest fires: ground, surface, and crown (Brown and Davis, 1973). Ground fires are fires that burn in the organic material below the litter layer, mostly by smouldering combustion. Surface fires burn in the litter, in other live and dead debris on the forest floor, and/or in small vegetation at or near the surface of the ground. Surface fires burn by flaming combustion. Crown fires also burn by flaming combustion but are located in the canopy of the trees. Crown fires remain connected to the surface fire from which they began or, rarely, they can become independent of the surface fire running ahead of it through the tree crowns. Crown fires are more intense than ground or surface fires. Most large fires that occur in the boreal forests of Canada are a mix of active crown fires, intermittent crown fires, and surface fires that create a mosaic of degrees of burning throughout the forest. The season during which fires occur also has ecological significance. Seasonality of fires determines succession trajectories post fire, and can affect regeneration capacity and fire intensity. For example, low intensity spring fires prior to leaf out can cause tree mortality in trembling aspen and birch (de Groot et al., 2003). If fires occur at this time they have been shown to girdle stems and prevent resprouting, but fires occurring after leaf flush can scorch leaves and promote aspen root suckering (Weber, 1990).

Lastly, the severity of fires, which relates to fuel consumption and is measured by depth of burn, influences post fire ecosystem structure and function. Fire severity impacts roots, underground reproductive tissues, and seed banks (McLean, 1969; Greene et al., 2007). For example, depth of burn of surface organic layers in black spruce (Picea Mariana (Mill.)) affects tree recruitment and vegetation recovery post fire (Landhaeusser and Wein, 1993; Gauthier et al., 1996). Greene et al. (2007) found that greater fire severity, due to prolonged smouldering around tree boles, resulted in thinner organic layers post burn. This was conducive to greater plant recruitment of small-seeded tree species (such as aspen) around the boles post-burn.

Due to the ecological influences of fire, patterns in the natural fire regime of the last few hundred years have shaped the forests we know today in Canada (Weber and Flannigan, 1997; Lertzman et al., 2002; Girardin et al., 2006a; Girardin et al., 2006b). Fire records prior to the past 40 to 50 years have been derived using proxy data from analysis of charcoal sediments, tree rings, and post-fire stand age distribution maps. These data can be used to put the current fire regime into a longer term context. Girardin et al. (2006a) showed that for Ontario (primarily the Boreal Shield Ecozone+), the fire regime in the 1940s to 1970s was the lowest fire activity in the past 200 years. They also showed that increases in the 1980s were still below levels recorded in the 1920s, around the time of increased human settlement, and much lower than levels recorded in the 1850s, the end of the Little Ice Age. These results concur with other findings for boreal Canada (Girardin et al., 2006b) and the eastern Canadian boreal (Bergeron et al., 2004; Bergeron et al., 2006; Gauthier et al., 2009). The frequency of large areas burned, especially in eastern Canada has declined since the 1850s. For areas outside the boreal forest, Lertzman et al. (2002) showed that very few fires have occurred in the temperate rainforest of British Columbia (Pacific Maritime Ecozone+) over the last 6,000 years, resulting in very large old-growth tree species like Sitka spruce (Picea sitchensis Bong. Carr.) and western hemlock (Tsuga heterophylla (Raf.) Sarg.).

More recently, humans have become an important factor in the fire regime, primarily over the last century. In the beginning of the 20th century, large fires, primarily caused by human activities, destroyed communities and caused significant loss of human life (Podur et al., 2002; Flannigan et al., 2009). These events led to fire management programs that were designed to detect and protect against unwanted fires. Fire suppression, especially since the 1970s with the advent of water bombers (Bergeron et al., 2001) and the use of helicopters for primary attack, has been very successful in some areas at reducing area burned by fires. Fire suppression techniques, particularly those directed at the initial stages of the fire, have been shown in Alberta and Ontario to reduce the proportion of large fires that occur, therefore reducing area burned in these boreal forest regions (Cumming, 2005; Martell and Sun, 2008). On the other hand, it has also been shown that when weather conditions are extreme suppression is less effective (Gauthier et al., 2005) and large fires occur regardless of suppression efforts. Nevertheless, as mentioned above, fire is a necessary disturbance in some of Canada’s forests. In order to balance the positive ecological benefits with the negative social and economic impacts, fire suppression has become a balancing act between maintenance of the ecological functions of fire and protecting human life and property (Flannigan et al., 2009).

The occurrence of fire from one year to the next is influenced by a complex set of factors which can be simplified into four categories: weather/climate, fuels, topography, and human influence (Flannigan and Wotton, 2001; Flannigan et al., 2005; Parisien et al., 2006). Weather influences fuel moisture and the occurrence of lightning ignitions. Severe fire weather, weather conditions that are most conducive to fire spread, is characterized by infrequent precipitation, warm temperatures, and high winds. Weather is a short term process having influence at the scale of the fire season or shorter, compared to climate which influences the atmosphere over longer periods (years to decades) (Flannigan and Wotton, 2001). Fuel structure, amount, moisture, and type all influence the propensity of the forest to burn. Topography influences the continuity of fuels, patterns of fuel moisture, and rate of spread. Humans act as both a source of ignition and of fire management through fire prevention education, suppression policies, and actions.

Regional variations in the factors that influence fire occurrence, as well as changes to the drivers themselves (such as climate change), have resulted in changes to the long-term fire regime across the country. This report provides a national synopsis highlighting changes and trends in the national fire regime and establishing patterns in the fire regime between different ecozones+ areas. More detailed information, including more information on long-term trends, is then provided for each ecozone+.

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Footnote 1

Environment Canada. 2006. Biodiversity outcomes framework for Canada. Canadian Councils of Resource Ministers. Ottawa, ON. 8 p.

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Footnote 2

Federal-Provincial-Territorial Biodiversity Working Group. 1995. Canadian Biodiversity Strategy: Canada's response to the Convention on Biological Diversity. Environment Canada, Biodiversity Convention Office. Ottawa, ON. 86 p.

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Footnote 3

Federal, Provincial and Territorial Governments of Canada. 2010. Canadian Biodiversity: Ecosystem Status and Trends 2010. Canadian Councils of Resource Ministers. Ottawa, ON. vi + 142 p.

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Footnote 4

Ecological Stratification Working Group. 1995. A national ecological framework for Canada. Agriculture and Agri-Food Canada, Research Branch, Centre for Land and Biological Resources Research and Environment Canada, State of the Environment Directorate, Ecozone Analysis Branch. Ottawa/Hull, ON. 125 p. Report and national map at 1:7 500 000 scale.

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Footnote 5

Rankin, R., Austin, M. and Rice, J. 2011. Ecological classification system for the ecosystem status and trends report. Canadian Biodiversity: Ecosystem Status and Trends 2010, Technical Thematic Report No. 1. Canadian Councils of Resource Ministers. Ottawa, ON.

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