The Once and Future Forest: Consequences of Mountain Pine Beetle Treatment Decisions

Entomologists and silviculturists have long recommended management of stand basal area and/or mean tree diameter to mitigate the risk of mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins) outbreaks while simultaneously reducing wildfire risk. In recent decades, however, wildfire suppression and reduced harvests in western North America have created a forest landscape that is densely stocked and increasingly susceptible to bark beetle infestations, especially as the climate becomes warmer and drier. We examine the various MPB treatment options available to land managers, including insecticides, semiochemicals, sanitation, and silvicultural treatments, and describe their long-term consequences in terms of risk of future bark beetle outbreaks, wildfire, invasion by exotic weeds, loss of hydrologic values, and carbon sequestration. Paradoxically, the treatments that are most enduring and best preserve the ecosystem services of North American forests are ones that result in some thinning of these stands. We, therefore, propose a renewed focus on silvicultural treatments over large spatial scales, particularly in lodgepole pine (Pinus contorta Douglas ex Loudon), and recommend semiochemical treatments, which may not protect all trees, for the protection of high-value trees, especially for high-elevation pines that grow in smaller stands. Prophylactic insecticide applications should be reserved for situations where any tree mortality at all is unacceptable.