Open Collections

Mitchell, Katherine Anne

University of British Columbia

Bark beetles (Coleoptera: Curculionidae: Scolytinae) and woodborers (Coleoptera: Buprestidae, Cerambycidae, Hymenoptera: Siricidae) are among the most important agents of tree mortality and decay in the phloem and sapwood of conifer tree species. Bark beetles and woodborers have been assumed to act independently, occupying distinct temporal niches throughout the death and decay processes of a conifer. However, interspecific interactions between bark beetles and woodborers may be more common than previously thought, with recent studies postulating that competition or predation from woodborers in the subcortical environment may be a notable, top-down constraint on bark beetle outbreaks. I evaluated the hypothesis that interspecific interaction between woodborers and bark beetles is a key driver of bark beetle irruptive dynamics, especially for pulse-driven irruptive species in the aftermath of broadscale forest disturbances. To address this, I studied Douglas-fir beetle (Dendroctonus pseudotsugae, hereafter DFB), a primary mortality agent of Douglas-fir, and the extent to which it interacts with woodborers following wildfires. Investigating the patterns of woodborer infestation post-fire, I found woodborers were frequent in stands with moderate fire-injury containing a living tree component, rather than stands following high-severity fire with near total mortality. Additionally, I found infestation was more likely in larger trees, suggesting woodborers selectively attack and kill mature conifers, which may otherwise survive their fire injuries. Investigating the extent of interspecific competition and/or predation by woodborers on bark beetles, I found DFB and woodborers were likely to attack trees with the same fire injury and stand characteristics. When co-infestation was high, woodborers successfully outcompeted DFB, indicating for the first time the result of interspecific interaction between these species following disturbance. Additionally, I found an apparent decoupling of pulse-driven DFB irruptions and fire that was associated with increasing disturbance rates across the Douglas-fir biome—an outcome consistent with widespread increases in woodborer populations over the same time period. My research has highlighted the need to quantify the role of top-down, interspecific pressures on the ability for bark beetles to outbreak, and how climate change may lead to the alteration of expected insect behaviour, particularly after widespread forest disturbances like wildfires.

Text

2025-03-27

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90545

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/