Ecology and Management of Bark Beetles

Abstract

Bark beetles (Coleoptera: Curculionidae: Scolytinae) have been considered a primary threat to forests throughout the northern hemisphere. Although tree mortality to bark beetles often detracts from forest management goals, the natural role of bark beetles is canopy opening, thinning, and diversification of stand structure and composition, effects that contribute to some ecosystem services in forests managed for multiple uses. Strategies to prevent bark beetle outbreaks exploit their sensitivity to host tree condition and spacing and their reliance on pheromones to attract sufficient numbers to overwhelm tree defenses. Tree species selection at planting or through selective thinning can favor tree species that are more tolerant of site conditions and resistant to bark beetles. Pre-commercial or commercial thinning improves tree condition and creates barriers to beetle population growth and spread. Remedial options include salvage harvest, pheromones for trap-out or disruption of host location, and white paint to disrupt the dark silhouette of the tree bole. Given the labor costs and trade-offs among tactics and the marginal profitability of fiber and timber production, harvest in advance of, or salvage harvest after, bark beetle attack often is the favored management strategy. However, this strategy is not as appropriate in public forests managed for values provided by older, more vulnerable trees. High-value sites for cultural values or endangered species protection may require use of more expensive management options.