Large outbreaks of native bark beetles (Dendroctonus spp.) are occurring throughout coniferous forests of western North America, from western Alaska to the U.S. Southwest and are believed to be related to climatic warming. In Colorado more than 270,000 ha of lodgepole pine forests have recently been infested by mountain pine beetle (MPB) (D. ponderosae), which has led to widespread public concern about increased fire hazard following beetle kill.
This research addresses four key questions about interactions of wildfire, outbreaks and climate and their potential cross-scale feedbacks in subalpine forests in northern Colorado. 1) How does climatic variation at seasonal, annual, and multi-decadal time scales affect the initiation and spread of MPB outbreaks across complex landscapes? 2) How does the landscape heterogeneity created by prior disturbance by fire affect the risk and/or spread of subsequent disturbance by MPB outbreak across complex landscapes? 3) How does the landscape heterogeneity created by prior disturbance by MPB affect the fuel hazard and risk of wildfire across complex landscapes? 4) How do context-specific contingencies between climate and the landscape affect the initiation and spread of wildfire and MPB outbreaks?
This project will examine possible feedbacks between wildfires and bark beetle outbreaks across different spatial scales and under varying climatic conditions. The research and associated outreach will improve understanding of the influence of beetle kill on future fire risk, which is of broad current interest to resource managers, the fire mitigation community and the public living in the bark-beetle affected areas.
This project has examined feedbacks between wildfire and bark beetle outbreak across different spatial scales and under varying climatic conditions in Colorado. Work on such feedbacks is a high priority in improving the predictive capacity of ecology, especially in relation to large-scale disturbances that potentially can affect vast areas of forest and that can threaten homes, communities, and other developments. This research has led to a number of important insights into how forest disturbances operate, with implications for both science and policy. One key finding is that past severe wildfires have historically reduced forest susceptibility to subsequent outbreaks of mountain pine beetle. But interestingly, this relationship does not hold true for the ongoing outbreak, possibly because the intensity of the ongoing outbreak is greater than that of previous outbreaks. Another major finding of this research was that over the past century wildfires in lodgepole pine forests have occurred during periods of drought. In contrast, bark beetle outbreaks did not increase the likelihood of wildfires. Thus, dry climatic conditions, rather than bark beetle outbreaks, determine fire risk in these forests. Although bark beetles do not increase fire risk, there is a real and present risk of wildfires due to recent drought across the western US. In this context, our research found that it would be possible to most effectively protect homes and communities from wildfire by removing flammable materials from the immediate vicinity of structures while incurring a fraction of the ecological and economic cost that would be incurred by cutting trees in forests that have been affected by bark beetles. As climate change is increasing the frequency, extent, and intensity of wildfires, insect outbreaks, and other forest disturbances, it is becoming more common for forests to be affected by more than one type of disturbance in a short time period. The effect of such multiple or compounded disturbances can be fundamentally different than the effect of single disturbances. In this context our research found that compounded disturbances can reduce the total amount of forest regeneration and may also lead to a transition of coniferous forests to aspen-dominated forests, which would have cascading effects on the ecology of those forests, including the possibility that forests may become less susceptible to wildfires and insect outbreaks. This project has improved understanding of various aspects related to the interactions among wildfires, bark beetle outbreaks and climate – including the influence of beetle kill on subsequent fire risk under varying climatic conditions, which is of broad current interest to resource managers, the fire mitigation community and the public living in the bark-beetle affected areas. Major national initiatives of fire risk mitigation and suppression, with annual expenditures on the order of $1 billion are currently being implemented in the western U.S. Specific management goals and expenditures have been driven by untested assumptions that beetle kill dramatically increases fire risk. This project examined such assumptions and analyzed the role of factors in addition to beetle kill that affect fire risk. In addition to publishing numerous scientific papers, the researchers involved in this work have testified before the United States Congress and have been interviewed by numerous newspapers and other news outlets in order to improve public understanding of these issues and to improve the degree to which policies are consistent with the best available science.
