Oregon State University

College of Earth, Ocean, and Atmospheric Sciences

Tracking Insect Outbreaks

Pine beetle impacted forest

View from Tam McArthur Rim of lodgepole pine and whitebark pine killed by mountain pine beetle within the prior 10 years, Deschutes County, OR in the Deschutes National Forest, September 2011. (Photo: Garrett Meigs, Oregon State University)

Satellite mapping techniques have given scientists a bird's-eye view of landscape changes over time. Assistant Professor Robert Kennedy and his former graduate student Garrett Meigs (now with the University of Vermont) have taken advantage of this technology to assess insect outbreaks and their effect on western U.S. forests over the last few decades.

Two of the offending culprits — the mountain pine beetle and western spruce budworm — are native species whose population numbers depend on a number of factors, including host tree health and climatic variability.

Under the right conditions, the insects can cause pervasive tree mortality and ensuing changes in forest structure and composition. Until recently, studies had not been able to assess the cumulative impacts of these outbreaks on regional forests.

The researchers used new computational techniques to link satellite imagery from NASA and the US Geological Survey with older data from airplane and ground surveys. Where old methods created the appearance of widespread, homogeneous insect activity, the new maps provide the fine spatial resolution necessary to better understand regional outbreaks since the 1980s.

Their analysis revealed that the budworm has affected a greater area and caused more total tree mortality than the mountain pine beetle, despite the beetle receiving more forest management attention. Beetle outbreaks also occurred in two phases — first during the 1970s and 80s in eastern and central Oregon and then later during the 2000s. Budworm outbreaks concentrated in northern Washington early on and spread from the eastern to central PNW during the 1980s, returning to northern Washington during the 1990s and 2000s.

This new mapping framework is important, researchers say, because it will help scientists and land managers learn how insects shape forests, and in turn how forests recover from outbreaks.

"Forests and insects dance to rhythms that are tricky to understand without good maps. We're excited to show how technology can blend with on-the-ground know-how to make those maps and lead to better management," Kennedy said.

In addition, the new mapping technique could be applied to the Pacific Northwest and other regions to assess when and where insect outbreaks result in substantial tree mortality. Kennedy said it makes way for additional research on the complex interactions between fire, insect outbreaks and climate change. For example, the team found recently that wildfire likelihood does not generally increase following mountain pine beetle outbreaks, despite popular sentiment to the contrary. In fact, wildfire likelihood appears to be lower following western spruce budworm outbreaks.

"Managing any natural resources under climate change requires knowledge of cause and effect. Maps like these provide us the tools to link the 'When?' and the 'Where?', and that's the first step toward understanding the 'Why?'"

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