Removing dead trees will not save us from fast-moving wildfires by Dominick DellaSala, et al., PNAS, 2025
“One well-studied example of the dead tree-fire assumption is the impact of bark beetle (Scolytinae) outbreaks across western North America. It shows that groups of lodgepole pine trees (Pinus contorta) killed by the beetles only pose a fire risk for one to three years while their needles remain attached. Once the needles drop, there’s no canopy fuel to drive fire through the crowns. And removing dead trees before needles drop would instead place fine fuels (logging slash) on the ground all at once.
“Thus, studies report no detectable changes in the likelihood of fire or area burned in beetle-affected snag forests . In general, research suggests that large patches of beetle killed trees are generally less flammable at broad scales, not more so.”
When Active Management of high conservation value forests may erode biodiversity and damage ecosystems by David Lindenmayer, et al., Biological Conservation, 2025
“[T]hinning kills far more trees than it prevents from being killed by drought and native bark beetles.”
Mountain Pine Beetle in Colorado: A Story of Changing Forests by Jose F. Negron et al., Journal of Forestry, 2018
“Another important question is whether beetle-caused tree mortality can increase the likelihood of fire occurrence. Limited work in lodgepole pine in Colorado suggests that this may not be the case. West (2010) sampled 57 burns in the Arapaho-Roosevelt and the White River National Forests, searching for locations where MPB-caused tree mortality had occurred in the 1980s. Evidence of MPB was found in only two burns.
“A spatial analysis of 466 fires (all but one less than an acre) from 1980 to 2005 did not find a relationship between MPB-caused mortality and subsequent fires. Kulakowski and Jarvis (2011) examined burned and unburned lodgepole pine stands and indicated that beetle-caused mortality did not increase fire probability. Observed fires were driven by climatic factors that foster dry conditions, which is consistent with previous studies.”
“Do insect outbreaks reduce the severity of subsequent forest fires?” by Garrett W Meigs, Harold S J Zald, John L Campbell, William S Keeton, Robert E Kennedy, Environmental Research Letters, 2016
“In contrast to common assumptions of positive feedbacks, we find that insects generally reduce the severity of subsequent wildfires. Specific effects vary with insect type and timing, but both insects decrease the abundance of live vegetation susceptible to wildfire at multiple time lags. By dampening subsequent burn severity, native insects could buffer rather than exacerbate fire regime changes expected due to land use and climate change.”
“Fire Severity Unaffected by Spruce by Spruce Beetle Outbreak in Spruce-Fir Forests in Southwestern Colorado” by Robert A. Andrus, Thomas T. Veblen, Brian J. Harvey, Sarah J. Hart, Ecological Society of America, 2015
“Contrary to the expectation that bark beetle infestation alters subsequent fire severity, correlation and multivariate generalized linear regression analysis revealed no influence of pre-fire spruce beetle severity on nearly all field or remotely sensed measurements of fire severity.”
“[B]eetle infestation did not alter fire severity.”
“Does Wildfire Likelihood Increase Following Insect Outbreaks in Conifer Forests?” by Garrett W. Meigs, John L. Campbell, Harold S. J. Zald, John D. Bailey, David C. Shaw, Robert E. Kennedy, Ecosphere, 2015
“In recent decades across the PNW, wildfire likelihood does not consistently increase or decrease following insect outbreaks.”
“Area Burned in the Western United States is Unaffected by Recent Mountain Pine Beetle Outbreaks” by Sarah J. Hart, Tania Schoennagel, Thomas T. Veblen, Teresa B. Chapman, Proceedings of the National Academy of Sciences (PNAS), 2015
“Contrary to the expectation that an MPB outbreak increases fire risk, spatial overlay analysis shows no effect of outbreaks on subsequent area burned during years of extreme burning across the West. These results refute the assumption that increased bark beetle activity has increased area burned.”
“Recent Mountain Pine Beetle Outbreaks, Wildfire Severity, and Postfire Tree Regeneration in the U.S. Northern Rockies” by Brian J. Harvey, Daniel C. Donato, Monica G. Turner, Proceedings of the National Academy of Sciences (PNAS), 2014
“We found that recent (2001–2010) beetle outbreak severity was unrelated to most field measures of subsequent fire severity, which was instead driven primarily by extreme burning conditions (weather) and topography.”
“Management for mountain pine beetle outbreak suppression: Does relevant science support current policy?” by Diana L. Six, Eric Biber, Elisabeth Long, Forests, 2014
“A study may report that 75% of trees in controls are killed by the beetle, whereas only 10% are killed in thinned stands. At first glance, this appears to be a resounding success in saving trees. However, if we approach this situation from a pretreatment perspective, our interpretation of success may change. In this example, 400 mature trees existed in each plot prior to treatment. After treatment, 100 mature trees remain in the thinned plots (300 trees have been removed by thinning). Doing the math, we find that once the beetles have run their course, more residual living trees (100) actually remain in the control plot than in the thinned plot (90) and, in fact, humans have contributed more to tree mortality than have the beetles.”
“[P]ost-infestation, untreated stands had more live spruce trees and greater basal areas. When comparing only residual large spruce, final densities in both stand types were similar. Six found higher numbers of mature living trees remained in control stands of ponderosa pine than in thinned stands post-mountain pine beetle outbreak.”
Bark Beetles Increase Biodiversity While Maintaining Drinking Water Quality, by Reed Noss, et al., Conservation Letters, 2014
“Our study provides strong support for a policy to allow natural disturbance-recovery processes to operate unimpeded in conifer-dominated mountain forests, especially within protected areas.”
Fire severity and tree regeneration following bark beetle outbreaks: the role of outbreak stage and burning conditions by Brian J. Harvey et al., Ecological Society of America, 2014
“In the green-attack/red stage, several canopy fire-severity measures increased with prefire outbreak severity under moderate burning conditions. Under extreme conditions, few fire-severity measures were related to prefire outbreak severity, and effect sizes were of marginal biological significance…
“In the gray stage, by contrast, most fire-severity measures declined with increasing outbreak severity under moderate conditions, and fire severity was unrelated to outbreak severity under extreme burning conditions.”
Do Bark Beetle Outbreaks Increase Wildfire Risks in the Central U.S. Rocky Mountains? Implications from Recent Research by Scott H. Black, Barry Noon, et al., Bio One, 2013
“While research is ongoing and important questions remain unresolved, to date most available evidence indicates that bark beetle outbreaks do not substantially increase the risk of active crown fire in lodgepole pine (Pinus contorta) and spruce (Picea engelmannii)-fir (Abies spp.) forests under most conditions. Instead, active crown fires in these forest types are primarily contingent on dry conditions rather than variations in stand structure, such as those brought about by outbreaks.
“Preemptive thinning may reduce susceptibility to small outbreaks but is unlikely to reduce susceptibility to large, landscape-scale epidemics. Once beetle populations reach widespread epidemic levels, silvicultural strategies aimed at stopping them are not likely to reduce forest susceptibility to outbreaks. Furthermore, such silvicultural treatments could have substantial, unintended short— and long-term ecological costs associated with road access and an overall degradation of natural areas.”
“Under some circumstances, thinning may alleviate tree stress at the stand level but is unlikely to be effective at mitigating susceptibility against extensive or severe outbreaks. Preisler and Mitchell found that thinned plots of lodgepole pine in Oregon were initially unattractive to mountain pine beetles; but when large numbers of attacks occurred, colonization rates were similar to those in unthinned plots. Similarly, Amman et al. studied the effects of spacing and diameter of trees and concluded that tree mortality was reduced as basal area was lowered. However, if the stand was in the path of an ongoing mountain pine beetle epidemic, spacing and density of trees had little effect.
“Post-disturbance harvest is common practice on forest lands and is designed to remove trees or other biomass in order to produce timber or other resources. This type of resource extraction has the potential to inadvertently lead to heightened insect activity. In particular, snags and fallen logs contribute to the protection of soils and water quality and provide habitat for numerous cavity and snag-dependent species, many of which prey on bark beetles and other economically destructive insects. Therefore, outbreaks could be prolonged because of a reduction in the beetle’s natural enemies, including both insects and bird species that feed on mountain pine beetles. Furthermore, post-disturbance harvest can damage soil and roots by compacting them leading to greater water stress in trees, which may reduce conifer regeneration by increasing sapling mortality and, in general, may cause more damage to forests than that caused by natural disturbance events.”
Effects of Mountain Pine Beetle on Fuels and Expected Fire Behavior in Lodgepole Pine Forests, Colorado, USA by Tania Schoennagel et al., PLOS One, 2012
[O]bserved fire behavior may not be qualitatively different among MPB [mountain pine beetle] stages under extreme burning conditions. Overall, the risk (probability) of active crown fire appears elevated in MPB-affected stands, but the predominant fire hazard (crown fire) is similar across MPB stages and is characteristic of lodgepole pine forests where extremely dry, gusty weather conditions are key factors in determining fire behavior.”
Do mountain pine beetle outbreaks change the probability of active crown fire in lodgepole pine forests? by Martin Simard et al., Ecological Society of America, 2011
“Our results suggest that mountain pine beetle outbreaks in Greater Yellowstone may reduce the probability of active crown fire in the short term by thinning lodgepole pine canopies.”
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