An assessment of Alberta's strategy for controlling mountain pine beetle outbreaks

Abstract

The Canadian province of Alberta spent over 500 million dollars on controlling mountain pine beetle populations, but did it work? Using a statistical modeling framework coupled with long-term field data, we examined how direct control measures, severe winters, and host-tree depletion shaped the trajectory of Alberta's mountain pine beetle outbreak between 2009 and 2020. Simulations suggest that control efforts reduced total tree mortality by 79% (95% predictive interval: 58--89%) and prevented 1.8 (0.91--4.1) trees per hectare from being killed from 2010--2020. Although cold winters had little effect on overall damage, they acted synergistically with control to end the outbreak, causing population collapse circa 2020. This synergy supports a "wait it out" strategy of mountain pine beetle management, where moderate control effort is applied until an extreme weather event delivers the final blow. Any effects of host-tree depletion via beetle attack were negligible. From an economic perspective, removing one infestation tree -- at an approximate cost of 320 CAD -- prevented the loss of roughly six (2.6--15) trees, demonstrating the potential for long-term cost-effectiveness. Our results further indicate that future outbreaks may vary widely in severity due to environmental stochasticity, with potential damage in a no-control scenario ranging from 0.41 to 9.7 trees per hectare killed (over a hypothetical 11-year period). An alternative model predicts an even wider range of outcomes: 1--40 trees per hectare. These findings highlight not only the potential of sustained control efforts in mitigating forest pest outbreaks, but also the inherent uncertainty in long-term ecological forecasting.