Canadian Forest Service Publications

Wildland fire deficit and surplus in the western United States, 1984-2012. 2015. Parks, S.A.; Miller, C.; Parisien, M.-A.; Holsinger, L.M.; Dobrowski, S.Z.; Abatzoglou, J. Ecosphere 6(12):Article 275.

Year: 2015

Available from: Northern Forestry Centre

Catalog ID: 36487

Language: English

CFS Availability: PDF (download)

Available from the Journal's Web site.
DOI: 10.1890/ES15-00294.1

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Abstract

Wildland fire is an important disturbance agent in the western US and globally. However, the natural role of fire has been disrupted in many regions due to the influence of human activities, which have the potential to either exclude or promote fire, resulting in a “fire deficit” or “fire surplus”, respectively. In this study, we developed a model of expected area burned for the western US as a function of climate from 1984 to 2012. We then quantified departures from expected area burned to identify geographic regions with fire deficit or surplus. We developed our model of area burned as a function of several climatic variables from reference areas with low human influence; the relationship between climate and fire is strong in these areas. We then quantified the degree of fire deficit or surplus for all areas of the western US as the difference between expected (as predicted with the model) and observed area burned from 1984 to 2012. Results indicate that many forested areas in the western US experienced a fire deficit from 1984 to 2012, likely due to fire exclusion by human activities. We also found that large expanses of non-forested regions experienced a fire surplus, presumably due to introduced annual grasses and the prevalence of anthropogenic ignitions. The heterogeneity in patterns of fire deficit and surplus among ecoregions emphasizes fundamentally different ecosystem sensitivities to human influences and suggests that large-scale adaptation and mitigation strategies will be necessary in order to restore and maintain resilient, healthy, and naturally functioning ecosystems.

Plain Language Summary

Wildfires have a natural ecological role. However, human activities exclude fire from some ecosystems and promote fire in others, and many areas are experiencing either a fire deficit or a fire surplus. We measured departures from the natural levels of fire activity (i.e., fire deficits and surpluses) from 1984 to 2012 in the western United States. We developed a model of fire activity as a function of climate from areas with low human influence (e.g., national parks); the relationship between climate and fire is strong in these areas. We then measured the degree of fire deficit or surplus for all areas of the western US as the difference between expected (as predicted with the model) and observed fire activity from 1984 to 2012. Most forested areas experienced a fire deficit during this period, probably because of fire exclusion by human activities. We also found that large expanses of non-forested regions experienced a fire surplus, presumably due to introduced annual grasses. Our results demonstrated that different ecosystems (e.g., forests versus grasslands and shrublands) have fundamentally different sensitivities to human influences. A variety of large-scale adaptation and mitigation strategies will be necessary to restore ecosystems to a resilient, healthy, and naturally functioning state.

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