Fig 2. A Mountain pine beetle burrowing into a pitch tube.
Background Mountain pine beetle (Dendroctonus ponderosae; MPB) is a forest insect native to western North American pine forests. It has historically been limited to small and scattered outbreaks in western North America [1, 2]. MPB is currently considered the most aggressive, persistent, and damaging pest to mature lodgepole pine forests in western North America; it is expanding in an unprecedented wave into novel areas at higher elevations, further north, and further east into west-central Alberta, where pine forests differ from historical MPB habitat [1, 3].
MPB has historically been a part of British Columbia’s natural disturbance regime, unlike Alberta where lodgepole pine (Pinus contorta Douglas) is adapted to stand-initiating wildfire [3, 4]. Much of the research done in Canada on MPB was conducted in British Columbia [3, 4], with only short term studies conducted in Alberta, and so as MPB progresses east it is unknown how Alberta’s lodgepole pine forests will respond to this new disturbance [4].
Research on forest responses to MPB often focuses on stand composition changes; little is known about responses of nutrients or understory vegetation. During MPB attacks, pine needles turn red (red-attack) within 2-3 years, begin to fall by the second year, and most foliage is lost (grey-attack) within 4-5 years after attack. These canopy changes can result in changes to light levels, nutrients, space, and moisture [5, 6, 7]. Pec et al. (2015) showed that understory vegetation responded immediately to MPB attacks, following a gradient of increased response with increased canopy death [6]. This contrasts studies by McIntosh & Macdonald [8] and Klutsch et al. [9] that found understory vegetation exhibited resistance to MPB attack in red-attack stage. Stone & Wolfe [7] and McCambridge et al. [10] found that canopy death in Utah and Colorado respectively increased understory vegetation abundance in grey attack stands. Understanding the responses of vegetation is important to determine the potential changes in biodiversity that may occur in these forests, as well as the potential for pine regeneration since understory vegetation can strongly influence tree regeneration [6].
Fig 3. The transition of green to red to grey attack stages after mountain pine beetle attack.
Fig 4. Understory vegetation located in a lodgepole pine forest in the study area.
Objectives The objectives of this study are to: 1) quantify effects of MPB attack and of salvage logging, including changes in light and moisture, on forest understory vegetation in a simulated MPB attack stand in west-central Alberta, 2) determine if understory vegetation still exhibits resistance to the effects of MPB (in simulated attack area) or if they have adapted to canopy changes accompanying grey attack stage (including light and moisture). This can be used to determine the likelihood of natural pine regeneration following MPB attacks and the most likely future forest structure and successional pathways that will be experienced.
Expected Results Although understory vegetation is not disturbed directly following MPB attacks, the severity of MPB attack may affect vegetation responses such as richness and diversity [7]. Higher severity attacks result in less canopy cover and therefore more light reaching the forest floor [5] as well as more moisture reaching the forest floor. Vegetation responses have been seen to peak under moderate levels of mortality [7]. In this study, I expect to see increased levels of light and moisture in more heavily disturbed stands, most likely resulting in increased understory vegetation cover, richness, and a change in composition.