How tiny insects are transforming western forests (and what we can do about it)

Bark beetles (Coleoptera: Curculionidae) are a crucial component of forest ecosystems with only roughly 20 of the 550 species native to North America causing significant economic damage. However, several of those 20 species can have an outsized influence in forest health and under the right conditions, can cause landscape-level tree mortality. Since 2000, bark beetles have impacted billions of trees across millions of hectares across western North America. These numbers were largely driven by a historic mountain pine beetle, Dendroctonus ponderosae Hopkins, outbreaks across the west, a major western pine beetle, D. brevicomis LeConte, outbreak in California, and ongoing spruce beetle, D. rufipennis (Kirby), outbreaks in Alaska and the Rocky Mountains. A century of fire suppression has resulted in overly dense, unhealthy, often even-aged forest stands. This combined with the effects of a warming climate and intensified, more frequent droughts have created the conditions for these mega-disturbance events. Bark beetle management broadly falls into two categories: Population suppression and prevention. Tools and strategies for population suppression include insecticides, semiochemical interruption, and sanitation. Prevention is primarily focused on active forest management to promote individual tree and stand level health. Techniques include mechanical thinning, prescribed fire, and restoration. The pros and cons for these strategies are discussed with a focus on integrated approaches to mitigate bark beetle disturbance events in an era of increasing weather and climate stressors.