Effectiveness of Verbenone and Green-leaf Volatiles in Protecting High-value Whitebark Pine Trees through a Mountain Pine Beetle Outbreak in Jasper National Park

The objective of this study is to determine how effective single-tree Verbenone and Green-leaf
Volatile treatments are in protecting high-value Whitebark pine trees from mountain pine
beetle infestation.

Although this treatment has shown to be very effective in other regions, it has never been formally evaluated for high value single-tree protection in Canada, including for endangered whitebark. Understanding its effectiveness during a high-infestation outbreak is essential to focus protection efforts and assign available resources to protect and help recover Whitebark and Limber Pine throughout their ranges in Canada.

Background

The recent mountain pine beetle outbreak in Jasper National Park extended into high elevation forests, facilitated by favourable climate conditions. Whitebark pine is a keystone species in tree line ecosystems across the Park, and it is listed under the Species at Risk Act as Endangered due to the combined effects of non-native white pine blister rust, mountain pine beetle, historic fire suppression and climate change.

The recovery of this species hinges on identifying and protecting whitebark pine trees that are naturally-resistant to white pine blister rust. Blister rust resistant individual trees are rare and extensive ground and aerial surveys have identified several hundred potentially resistant trees of the tens of thousands of trees surveyed. These individual trees are being tested to prove their rust resistance, a process that takes 7 years in a controlled facility. Recovery of this species depends on collecting seeds, and growing and planting seedlings from rust-resistant trees.

Protecting blister rust-resistant trees from mountain pine beetle is critical to recovery. Beetle infestation was absent in whitebark pine stands in Jasper prior to the recent outbreak. Starting in 2015, rust-resistant trees were annually protected from mountain pine beetle attack through the use of high dose Verbenone combined with Green-Leaf Volatiles. These pheromones mimic a fully attacked trees’ chemical signals, which helps repel attacking beetles. The peak of the outbreak in high elevation forest was between 2016 and 2018. Very cold winter conditions in 2019 caused high (~98%) beetle mortality.

Annual surveys found that some treated, rust-resistant whitebark pine trees were killed by beetle. The application of Verbenone and GLV on rust-resistant trees is expensive and time consuming. Although this treatment has shown to be very effective in other regions, understanding its effectiveness during a high-infestation outbreak is essential to focus protection efforts and assign available resources to protect and help recover Whitebark and Limber Pine throughout their ranges in Canada.