Bark Beetles: Not All Bad? - Rocky Mountain Research Station - RMRS

The bark beetle is always cast as the villain in the story of the tree die-offs in western forests. But despite the harm to the scenic view and the impact on recreation and management for forest products, bark beetles play important roles in the forest ecosystem health.

Native bark beetles help regulate the structure of forest stands and forest productivity. They also play an important role in species diversity and in biogeochemical cycling—the movement of elements through the ecosystem. Researchers are working through a long list of questions about how bark beetles affect ecosystems—aside from changing the scenery.

Bark beetle infestations create patches of forest that have trees of various ages, densities, species, and successional stages. This variation helps keep the forests healthy. Researchers are looking at ways to connect bark beetle activity with landscape patterns so they can better measure—and better understand—the beetle’s ecological role.

Researchers are also trying to determine whether practices such as forest thinning can help mitigate extensive tree mortality caused by bark beetles. Most studies addressing thinning have been conducted on small plots and areas with even-aged stands and few forest types. Forest managers and researchers plan to apply these findings to large landscapes to determine how forest thinning affects the beetle outbreaks.

Another research priority is sorting out the complicated interactions between bark beetles and forest fires. Interactions between bark beetles and fire take two forms. First, fire can injure trees and change the volatile emissions of conifers, a process that often increases the trees’ susceptibility to some bark beetles. Second, bark beetles can change the forest environment by influencing forest structure and transforming fuels. Overall, wildfire risk following beetle outbreaks, although not well understood, might depend on interactions with several factors. Some of these include tree cover types, site characteristics, changes in forest structure, and time since mortality—among others.

Scientists also are looking at the effects of climate change on beetle biology and outbreaks, which recently have coincided with increased winter temperatures and changing precipitation patterns. Climate change affects bark beetles by altering their development, temperature-induced mortality, and the way they select their hosts. Climate change will also affect trees’ defense mechanisms against bark beetle attacks.

Although researchers are considering the potentially good effects of outbreaks, they continue to look for ways to mitigate tree mortality. One area that shows promise is the potential use of semiochemical substances rather than insecticides. Semiochemicals are substances produced by organisms that regulate behavior, particularly the way beetles attack their host trees. For example, researchers are looking at the use of substances that might signal to beetles that a tree is outside their host range.

Bark beetles are causing a significant change to western forest scenic landscapes. Scientists are pursuing several lines of research that address the negative effects of beetles and help us understand the beetle’s positive influences.