Prescribed Fire Does Not Promote Outbreaks of a Primary Bark Beetle at Low-density Populations

The causes of bark beetle outbreaks – particularly the role of disturbances – are poorly understood. Stand‐scale disturbances, like fires, can suddenly improve local host susceptibility and may attract beetles; however, whether such increases can lead to outbreaks in post‐disturbance stands is unclear. Using low‐density Dendroctonus ponderosae mountain pine beetle populations in Pinus contorta lodgepole pine forests in western Canada, we investigated whether prescribed fires promote outbreaks or provide only short‐term resources. Proportionally more burned than non‐burned trees were attacked. At one site, beetle attacks increased in response to a resource pulse, but the proportions of attacked trees and numbers of attacks per tree declined over four years after fire. Elsewhere, beetle attacks remained very low. As the resource (phloem) quality of burned trees remained high three years after fire, we propose that post‐fire mortality, resulting in fewer available host trees, can at least partially explain why D. ponderosae did not build up populations in burned stands. Synthesis and applications. Our study emphasizes the importance of examining long‐term trends in fire–bark beetle interactions, and of understanding low‐density beetle populations. Because fire does not seem to promote mountain pine beetle outbreaks, we recommend the continued use of prescribed fire for the general management of P. contorta forests with low‐density beetle populations