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Bark Beetles

Mountain Pine Beetle
Mountain Pine Beetle

Along the West Coast through the Rocky Mountains, bark beetles have affected tens of millions of acres of forest. While bark beetles are native to U.S. forests and play important ecological roles, they can cause extensive tree mortality and negative economic and social impacts. Climate change has led to an increase in these damaging effects, and the Forest Service is working to better understand bark beetle ecology and to improve forest management.

Bark beetles are tiny insects with hard, cylindrical bodies that reproduce under the bark of trees. There are 600 different species of bark beetles in the United States. Several species, such as the mountain pine beetle (Dendroctonus ponderosae), attack and kill live trees. Most species of bark beetles live in dead, weakened, or dying hosts.

Bark beetles are important disturbance agents in western coniferous forests. Population levels of a number of species oscillate periodically, often reaching high densities and causing extensive tree mortality when favorable forest and climatic conditions coincide. These events are part of the ecology of western forests and positively influence many ecological processes, but their adverse economic and social implications can also be significant.

During the past decade in the west, tree mortality caused by bark beetles has increased in spruce, lodgepole, pinyon-juniper, and ponderosa forests. This increase is correlated with shifts in temperature and increased water stress, which create conditions within trees that are favorable to beetle survival and growth. A synthesis of climate change effects on native bark beetles, important mortality agents of conifers in western North America, is available at Climate Change and Bark Beetles of the Western United States and Canada.

Over the past century, USDA Forest Service research scientists have studied the biology, ecology and management of tree killing bark beetles. This knowledge serves as a foundation to respond to current issues. Historically, research reflected an emphasis on protecting timber resources. Today, changes in societal values, climate, global trading practices, and an increased awareness of the importance of disturbances in the functioning of forest ecosystems present previously unexplored questions.

Because of the significant impacts of bark beetles, the three western Forest Service research stations Pacific Northwest Research Station, Pacific Southwest Research Station and Rocky Mountain Research Station formed the Western Bark Beetle Research Group (WBBRG) to enhance responsiveness, delivery, and impact of bark beetle research by strengthening cooperative working relationships among researchers and partners. The WBBRG assembled a synthesis of current mountain pine beetle knowledge, published in 2014 in Forest Science. The synthesis covers a wide array of topics, including chemical ecology, vegetation management to reduce susceptibility, landscape dynamics, associated organisms, new findings on insect development, and the consequences of treatment decisions.

To respond to unprecedented bark beetle mortality (41.7 million acres across multiple ownerships) in 2011, the WBBRG outlined a strategy to avoid hazards from falling trees, fires, utilize biomass and manage forests for resiliency.

Find research publications about bark beetles on Treesearch.