title: Area burned in the western United States is unaffected by recent mountain pine beetle outbreaks.
abstract: In the western United States, mountain pine beetles (MPBs) have killed pine trees across 71,000 km(2) of forest since the mid-1990s, leading to widespread concern that abundant dead fuels may increase area burned and exacerbate fire behavior. Although stand-level fire behavior models suggest that bark beetle-induced tree mortality increases flammability of stands by changing canopy and forest floor fuels, the actual effect of an MPB outbreak on subsequent wildfire activity remains widely debated. To address this knowledge gap, we superimposed areas burned on areas infested by MPBs for the three peak years of wildfire activity since 2002 across the western United States. Here, we show that the observed effect of MPB infestation on the area burned in years of extreme fire appears negligible at broad spatial extents. Contrary to the expectation of increased wildfire activity in recently infested red-stage stands, we found no difference between observed area and expected area burned in red-stage or subsequent gray-stage stands during three peak years of wildfire activity, which account for 46% of area burned during the 2002-2013 period. Although MPB infestation and fire activity both independently increased in conjunction with recent warming, our results demonstrate that the annual area burned in the western United States has not increased in direct response to bark beetle activity. Therefore, policy discussions should focus on societal adaptation to the effects of recent increases in wildfire activity related to increased drought severity.
authors.affiliation: Department of Geography, University of Colorado, Boulder, CO 80302; and sarah.hart@colorado.edu.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Hart
authors.affiliation: Department of Geography, University of Colorado, Boulder, CO 80302; and Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80303.
authors.forename: Tania
authors.initials: T
authors.lastname: Schoennagel
authors.affiliation: Department of Geography, University of Colorado, Boulder, CO 80302; and.
authors.forename: Thomas T
authors.initials: TT
authors.lastname: Veblen
authors.affiliation: Department of Geography, University of Colorado, Boulder, CO 80302; and.
authors.forename: Teresa B
authors.initials: TB
authors.lastname: Chapman
mesh_terms: D000818:Animals; D001517:Coleoptera / Q000502:physiology*; D004196:Disease Outbreaks; D055864:Droughts; D005390:Fires; D065928:Forests; D005843:Geography; D028223:Pinus; D013696:Temperature; D014197:Trees; D014481:United States
keywords: Dendrocotnus ponderosae; bark beetle; disturbance interactions; lodgepole pine; wildfire
references.citation: PLoS One. 2012;7(1):e30002
references.pmid: 22272268
references.citation: Ecology. 2010 Oct;91(10):2833-49
references.pmid: 21058545
references.citation: Nature. 2008 Apr 24;452(7190):987-90
references.pmid: 18432244
references.citation: Ecology. 2012 Oct;93(10):2175-85
references.pmid: 23185879
references.citation: Ecol Appl. 2012 Oct;22(7):1876-91
references.pmid: 23210306
references.citation: Proc Natl Acad Sci U S A. 2014 Oct 21;111(42):15120-5
references.pmid: 25267633
references.citation: Ecology. 2007 Nov;88(11):2891-902
references.pmid: 18051658
references.citation: Ecology. 2012 Nov;93(11):2421-34
references.pmid: 23236913
references.citation: Ecol Appl. ;24(7):1608-25
references.pmid: 29210226