Pine beetles don’t support forest fires

One of the greatest challenges for contemporary ecology is to predict the consequences of climate change on ecosystems. This post discusses the connection between pine beetles outbreaks and forest fires in the western United States. Read more what scientists from University of Colorado have recently found.

Mountain pine beetles and forest fires

Abundant susceptible pine hosts and a suitable climate during the early 21st century have promoted widespread mountain pine beetle outbreaks. Everybody can agree, that climate is changing, whether induced by humans or sun:

Global warming is due to sun’s radiation – NOT carbon emissions!

Nevertheless, climate is a vital factor on disturbances, including fire and insects outbreaks. Mountain pine beetle is classified as one of the most destructive forest insects in North America, and during outbreaks, high levels of tree mortality occur across large landscapes. Many scientists and forest professionals hypothesized that mountain pine beetle outbreaks are leading to concern that dead fuels may increase wildfire risk. This is due to beliefs that mountain pine beetle-induced tree mortality may be a significant factor, which affects fire behavior by altering the flammability, continuity, and structure of fuels.

Western United States

In consequence, mountain pine beetles have killed pine trees across 71 000 kmof forests in the western United States since the mid-1990s (map below).

mountain pine beetles outbreaks and fires
Major wildland fires in 2006, 2007, and 2012 that intersect mountain pine beetles hosts and cumulative mountain pine beetles infestation in 200-2012 across the western US

Scientists from University of Colorado decided to check the hypothesis if area burned in the western United States has been affected by recent mountain pine beetles outbreaks. In order to determine if mountain pine beetles infestation affects are burned at a broad spatial scale, scientists analyzed spatial data of mountain pine beetle infestation and area burned across the western United States (exclusive of Alaska).


Contrary to the expectation that a mountain pine beetle outbreak increases fire risk, spatial analysis showed no effect of outbreaks on area burned during years of extreme burning across the West. Scientists concluded:

“These results refute the assumption that increased bark beetle activity has increased area burned; therefore, policy discussions should focus on societal adaptation to the effects of the underlying drivers: warmer temperatures and increased drought”

In addition to these results, scientists under the leadership of Garrett Meigs from College of Forestry at Oregon State University went one step forward. They found this year that insects generally reduce the severity of subsequent wildfires. They supported their result with finding that insects decrease the abundance of live vegetation susceptible to wildfire at multiple time lags. In such situation, native insects buffer rather than exacerbate fire regime changes expected due to land use and climate change. At the end of their study they gave a following recommendation :

” […] we recommend precautionary approach when designing and implementing forest management policies intended to reduce wildfire hazard and increase resilience to global change”

Photo credit: Rafal Chudy


Hart S.J., T. Schoennagel, T.T. Veblen, T.B. Chapman. 2015. Area burned in the western United States is unaffected by recent mountain pine beetle outbreaks. PNAS, vol.112, no.14, 4375-4380. 

Meigs G.W., H.S.J. Zald, J.L. Campbell, W.S. Keeton, R.E. Kennedy. 2016. Do insect outbreaks reduce the severity of subsequent forest fires? Environ. Res. Lett. 11 (2016) 045008 

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