Prescribed fire does not promote outbreaks of a primary bark beetle at low‐density populations

Abstract

Summary 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.

Assessing spatiotemporal relationships between wildfire and mountain pine beetle disturbances across multiple time lags

“…, Fettig and McKelvey , Tabacaru et al. ). As with our observations of wildfire following MPB infestation, the increases were highly influenced by a few extreme observations in specific fire years (especially fire year 2006; Figs.…”

“…Although fires may not always facilitate subsequent MPB epidemics, especially when MPB populations are in the low‐density endemic phase, they may contribute to MPB population increases when they coincide with other drivers that favor successful colonization of host trees (Tabacaru et al. ).…”

Mountain Pine Beetle Dynamics and Reproductive Success in Post-Fire Lodgepole and Ponderosa Pine Forests in Northeastern Utah

“…These barriers include interspecific competition, host resistance, substrate quality, availability of susceptible hosts, and additional region-wide favorable conditions arising from weather, forest structure or both [9]. This study and others suggest that mountain pine beetle be considered in post-fire management, but that wildfire is not likely to cause transitions into new outbreaks [8, 9, 21, 52], due to the ‘pulsed resource’ [8] nature of fire-injured trees. Additional research should focus on mountain pine beetle response post-fire, in particular on mechanisms of attraction to and physiology of fire-injured trees, the role of beetle immigration, and potential for landscape-level spread beyond fire boundaries when other drivers such as drought and high temperature are present.…”

Fifty years of wildland fire science in Canada

“…The Fairholme was a success despite extreme summer drought conditions in a season when many challenging fires burned in Canada's national parks and the western provinces. Lessons learned in 2003 led to many changes in prescribed fire planning, smoke management, mountain pine beetle management (Trzcinski and Reid 2008;Tabacaru et al 2016), and resource allocation within Parks Canada. Similarly, a dozen national parks across Canada were now using fire to maintain ecological integrity.…”