Does Wildfire Likelihood Increase Following Insect Outbreaks in Conifer Forests? 1,3, 1 1 1 GARRETT W
Does wildfire likelihood increase following insect outbreaks in conifer forests? 1,3, 1 1 1 GARRETT W. MEIGS, JOHN L. CAMPBELL, HAROLD S. J. ZALD, JOHN D. BAILEY, 1 1,2 DAVID C. SHAW, AND ROBERT E. KENNEDY 1College of Forestry, Oregon State University, Corvallis, Oregon 97331 USA 2College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331 USA Citation: Meigs, G. W., J. L. Campbell, H. S. J. Zald, J. D. Bailey, D. C. Shaw, and R. E. Kennedy. 2015. Does wildfire likelihood increase following insect outbreaks in conifer forests? Ecosphere 6(7):118. http://dx.doi.org/10.1890/ ES15-00037.1 Abstract. Although there is acute concern that insect-caused tree mortality increases the likelihood or severity of subsequent wildfire, previous studies have been mixed, with findings typically based on stand- scale simulations or individual events. This study investigates landscape- and regional-scale wildfire likelihood following outbreaks of the two most prevalent native insect pests in the US Pacific Northwest (PNW): mountain pine beetle (MPB; Dendroctonus ponderosae) and western spruce budworm (WSB; Choristoneura freemani). We leverage seamless census data across numerous insect and fire events to (1) summarize the interannual dynamics of insects (1970–2012) and wildfires (1984–2012) across forested ecoregions of the PNW; (2) identify potential linked disturbance interactions with an empirical wildfire likelihood index; (3) quantify this insect-fire likelihood across different insect agents, time lags, ecoregions, and fire sizes. All three disturbance agents have occurred primarily in the drier, interior conifer forests east of the Cascade Range. In general, WSB extent exceeds MPB extent, which in turn exceeds wildfire extent, and each disturbance typically affects less than 2% annually of a given ecoregion.
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