Kick ‘em while they’re down: Do secondary bark beetles kill residual pines left by epidemic mountain pine beetle Dendroctonus ponderosae (Hopkins) in interior British Columbia?

Dendroctonus ponderosae (Hopkins), or mountain pine beetle (MPB), is a natural disturbance agent found throughout pine forests of British Columbia, Canada. All pines are suitable hosts for D. ponderosae, but in British Columbia, the primary host is lodgepole pine (Pinus contorta var. latifolia Engelmann). D. ponderosae has killed mature pines over a cumulative area of 15 million hectares in British Columbia and Alberta, or a total of 630 million cubic meters of timber in British Columbia, since the outbreak began around 1997. D. ponderosae typically acts as a biotic disturbance that maintains forest hygiene by removing weakened and decadent trees at endemic populations, but in outbreak situations, that same agent can exert a landscape-level mortality. As D. ponderosae depletes the larger trees in outbreak situations, there is a correlation of more suitable materials for secondary bark beetles with D. ponderosae associated species, such as Ips pini (Say) and Pseudips mexicanus (Hopkins). These secondary bark beetles may sustain the outbreak, since at high-density population levels, secondary bark beetles may kill healthy, smaller-diameter, residual-trees within the stands, in which D. ponderosae do not compete or reproduce very well. This study examines the stand-level interactions between the bark beetle species and their association with residual trees at the post-outbreak stage of D. ponderosae in the north central region of British Columbia. This has management implications for planning the future timber harvest and for future preventive measures as the surviving trees are evaluated – examining their species, vigour, and the rate of tree mortality.