Canadian Forest Service Publications
The spatially varying influence of humans on fire probability in North America. 2016. Parisien. M.-A.; Miller, C.; Parks, S.A.; DeLancey, E.R.; Robinne, F.-N.; Flannigan, M.D. Environmental Research Letters 11(7):075005.
Issued by: Northern Forestry Centre
Catalog ID: 37073
Availability: PDF (download)
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Humans affect fire regimes by providing ignition sources in some cases, suppressing wildfires in others, and altering natural vegetation in ways that may either promote or limit fire. In North America, several studies have evaluated the effects of society on fire activity; however, most studies have been regional or subcontinental in scope and used different data and methods, thereby making continent-wide comparisons difficult. We circumvent these challenges by investigating the broad-scale impact of humans on fire activity using parallel statistical models of fire probability from 1984 to 2014 as a function of climate, enduring features (topography and percent nonfuel), lightning, and three indices of human activity (population density, an integrated metric of human activity [Human Footprint Index], and a measure of remoteness [roadless volume]) across equally spaced regions of the United States and Canada.Through a statistical control approach,whereby we account for the effect of other explanatory variables, we found evidence of non-negligible human–wildfire association across the entire continent, even in the most sparsely populated areas. A surprisingly coherent negative relationship between fire activity and humans was observed across the United States and Canada: fire probability generally diminishes with increasing human influence. Intriguing exceptions to this relationship are the continent’s least disturbed areas, where fewer humans equate to less fire.These remote areas, however, also often have lower lightning densities, leading us to believe that they may be ignition limited at the spatiotemporal scale of the study.Our results suggest that there are few purely natural fire regimes in North America today.Consequently, projections of future fire activity should consider human impacts on fire regimes to ensure sound adaptation and mitigation measures in fire-prone areas.
Plain Language Summary
In projecting future wildfires and in adapting to climate change and mitigating its effects in areas prone to fires, it is important to understand the effect of humans on fire activity. This study looked at the relationship between wildfires and humans for all of Canada and the United States from 1984 to 2014. It created statistical models taking into account effects of climate, the type of terrain and amount of fuel, lightning as well as various ways of measuring human influence, such as population density and average distance to roads. The analysis showed that the importance of factors varied from one part of the continent to another, but climate and human influence were the most important factors in all areas. Almost everywhere, human activity lowered fire activity. An exception was some very remote areas with little human influence, where fire activity was also low. The effect of people is mixed: on one hand, people inadvertently start forest fires, but on the other hand, they also fight wildfires and cut down trees, preventing fire. The study found that there are few truly natural fire regimes in Canada and the United States today. This study is only one building block in understanding human impacts on wildfire, which must be taken into account in predicting fire risk.