Climate Change Fuelling Spruce and Mountain Pine Beetle Outbreaks

By: Katelyn Brown

Climate warming projections are anticipated to be between 1.8-4.0° Celsius by 2100 (IPCC, 2007), with much of this warming temperature due to rising carbon concentrations in the atmosphere due to anthropogenic activities. Beetle life cycles are extremely temperature dependent, and small changes in temperature and precipitation have profound effects on their development, reproduction, and success within an environment. Current Spruce and Mountain Pine Beetle outbreaks in the Western United States and Canada are being exacerbated by the already warming climate, and causing millions of hectares of mature pine forests to be destroyed, researchers say.

Researchers analyzed past temperature, precipitation and topography patterns and also created a cold tolerance model and weather projection model to predict future shift in temperature, precipitation, and ecosystem responses. This information was then compared to current and past beetle outbreaks in order to determine the correlations between a changing climate and the success of both the Spruce and Mountain Pine Beetle.

They found a direct positive relationship between rising temperatures and more frequent precipitation with the increase in number and severity of bark beetle outbreaks. It was also shown that as temperatures rose, the location of beetle outbreaks not only expanded in size but shifted northward as well, into areas not before suitable for the beetles or their host trees. Because of this shift northward, a dramatic change in ecosystem composition has been observed and is expected to continue.

Researchers also noted that a warming climate will have many direct effects on the life cycle and survival of both beetles. Rising temperatures will reduce cold mortality, and also allow beetles to change the timing of their life cycles (reproduction and development) in a way that will allow them to further reduce mortality. Researchers suggest that if the beetles are able to adapt to a changing climate in this way, it will allow for exponential population growth, which would allow the Spruce and Mountain Pine Beetle to continue to destroy hectares of forest.

Indirect effects of a warming climate on these beetles are also of great concern, researchers say. With rising temperatures, an increase in drought and forest fires are likely to occur. If they do, these events will lower the defences of host trees which will make it easier for the beetles to coordinate outbreaks. Furthermore, because the beetles and host trees are expected to move their range northward, changes in ecosystem composition will also lead to a shift in competition and predation. This could further allow the Spruce and Mountain Pine Beetle populations to flourish, allowing for more frequent and severe outbreaks.

Finally, as millions of hectares of mature pine forests are being destroyed, carbon storage is decreasing immensely. This is causing a carbon feedback system, where increased carbon is already present in the atmosphere due to anthropogenic activity and causing rising temperatures, because carbon storage is decreasing, carbon concentrations in the atmosphere are increasing at an even faster rate. If this cycle is to continue it could contribute to temperatures rising even higher and more steadily, which may further allow both the Spruce and Mountain Pine Beetle to continue to shift their range northward and coordinate mass outbreaks, allowing for continued destruction of mature pine forests.

Based on what researchers found, it is likely that as the climate continues to warm, negative impacts on the environment caused by bark beetle populations will also continue. Direct and indirect effects will cause not only the adaptation of the beetles themselves and their lifecycles but also cause changes in forest composition and the elevation of atmospheric carbon levels. Further monitoring of bark beetle outbreaks and changes in climate are needed to assess the situation more fully, and control methods need to be implemented to try and reduce the impact these beetle outbreaks are having on millions of hectares of forest, both in the United States and Canada.

References:

Bentz, B.J., Regniere, J., Fettig, C.J., Hansen, M.H., Hayes, J.L., Hicke, J.A., Kelsey, R.G., Negron, J.F., and Seybold, S. 2010. Climate change and bark beetles of the western united states and Canada: Direct and indirect effects. Bioscience. 60 (8): 602-613.

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