Is understory vegetation still resistant to mountain pine beetle attacks in lodgepole pine forests in western Alberta?
Fig 1. A MPB-killed stand in grey attack stage, located in west-central Alberta.
Summary Mountain pine beetle (MPB) is a native forest insect that is currently expanding into unprecedented areas in west-central Alberta, where lodgepole pine forests are adapted to fire. Canopy changes caused by MPB can impact nutrients, moisture, and light levels in a stand, which can in turn can alter understory vegetation. Understory vegetation has experienced immediate changes in some stands, while vegetation in others has exhibited a resistance to MPB in others. The objectives of this study are to quantify the effects of MPB attack in Alberta by conducting an experimental study in west-central Alberta, and to determine if understory vegetation still exhibits resistance to the effects of MPB. MPB attack was simulated by stem injections with glyphosate resulting in a pattern of stand-level mortality that closely resembles that following MPB attack. Treatments included: high mortality, medium mortality, simulated salvage logging operation, and untreated control; each treatment was replicated three times. Stands were sampled for percent canopy cover, soil moisture, and understory vegetation one year prior to disturbance, the year treatments were applied, one-year post-treatment, and five and seven years post-treatment. Vegetation richness and cover decreased initially in the salvage treatment, but cover has since recovered and richness has increased by 30%. Graminoid cover was 3.5 times higher in the salvage compared to control, while bryophyte level was 1.5 times lower in the salvage compared to the control. Forb and shrub cover only decreased following salvage logging, and in 2016 forb cover was 50% lower than pre-treatment levels, and shrub cover was 20% lower. While overall vegetation cover and richness did not indicate any changes to vegetation in grey-attack stage, closer examination of functional groups indicated changes to community composition within the differing treatments, indicating that this grey-attack stand in Alberta is no longer resistant to MPB.
Disclaimer: This website was created as part of a course project. All findings are preliminary and may be modified.