Changing Boreal Wildfire and Bark Beetle Outbreak: Implications for Ecosystems and People

 Mar 19, 2013    by Winslow Hansen

The following is a report of my Master’s research. To view a recording of my full defense click here.

Across the North American boreal forest, warming temperature trends have led to increases in the frequency and severity of wildfire and spruce bark beetle outbreak. For example, studies suggest that, by the end of the 21st century, annual area burned in the North American boreal forest is likely to expand by 74 to 118 percent. On the Kenai Peninsula in south-central Alaska, a series of warmer than average summers led to an epidemic spruce bark beetle outbreak that extended over 1.2 million hectares, between 1990 and 2000, and killed an estimated 30 million trees per year.Increases in large-scale disturbance are likely to have very important impacts on northern ecosystems and society, including changes to the nature of post-disturbance forest regeneration, thawing permafrost, and damage to peoples’ homes.

Increases in large-scale disturbance are likely to have very important impacts on northern ecosystems and society, including changes to the nature of post-disturbance forest regeneration, thawing permafrost, and damage to peoples’ homes.

While changing warming is an important and relatively well studied driver of the changes that are occurring in boreal wildfire and spruce bark beetle outbreak, characteristics and processes of the system in which these disturbances act also have an important influence on their behavior. For example, studies conducted in the Rocky Mountains suggest that the occurrence of one type of disturbance can change the characteristics of other types. To develop a more comprehensive understanding of changing boreal disturbance regimes and their social and ecological implications I asked two questions.

  1. To what extent did the spruce bark beetle outbreak on the Kenai Peninsula, AK affect the probability of subsequent wildfire?
  2. How did the spruce bark beetle outbreak and wildfire affect human wellbeing in exurban areas of the Kenai Peninsula, as measured by their effects on property values?

Using geo-spatial data I developed regression models to address both these questions. I found some pretty interesting things. First, the ecological impacts of the spruce bark beetle outbreak didincrease the probability of subsequent large wildfire (>500 ha), but not small wildfires. These were predominately controlled by human activity, instead of the beetle outbreak. I hypothesize two factors contribute to the increase in large wildfire probability. First, following the bark beetle outbreak there has been a significant increase in surface fuel loads on the Kenai Peninsula. Surface fuels are an important contributor to wildfire probability. Secondly, it has been shown in British Columbia, Canada that forest surface temperatures are higher in bark beetle-affected stands as compared to non-affected stands. On the Kenai Peninsula, the bark beetle outbreak may have further amplified the effects of a warming climate on boreal wildfire. However, the most important take-away message from these results is that understanding how warming temperature trends will influence boreal wildfire and bark beetle outbreak will require accounting for confounding system-specific factors, such as the occurrence of other disturbances and the influence of human behavior.

Because the action of people played such an important role in mediating interactions between bark beetle outbreak and wildfire, I also evaluated how both disturbances affected people, as measured by the disturbances’ effects on property values. It is likely that how people perceive these disturbances, affects their behavior as it relates to the potential for future disturbance probability. I found that, most often, the occurrence of spruce bark beetle outbreak and wildfire increased the property values of homes located nearby. At first, this is counter-intuitive. However, when one considers the context of the Kenai Peninsula, it begins to make sense. Before the occurrence of a disturbance, people’s views from their homes were obscured by dense forest. After the disturbance, views of Cooke Inlet and the mountains beyond emerge. It appears the benefits of an aesthetically-pleasing view outweigh the costs of fire and bark beetle outbreak.

While this finding is specific to the Kenai Peninsula, as views of Cooke Inlet are not found everywhere, the results of this study do raise some important points. For example, people do not necessarily perceive the consequences of wildfires and bark beetle outbreak negatively. Instead, they seem to form their viewpoints based on weighing the tradeoffs between costs associated with disturbances and their benefits. Understanding how people come to perceive wildfire and bark beetle outbreak could yield really valuable management insight. Understanding peoples’ perceptions, and shaping management strategies accordingly, could help us bolster public support for implementing new tools that effectively balance the integral ecological role disturbance often plays with public safety. 

Photos courtesy of Ann Olsson, Winslow Hansen, and Climate.org

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Boreal wildfire

Boreal wildfire