Verbenone decreases whitebark pine mortality throughout a mountain pine beetle outbreak

Authors: PERKINS, DANA - Bureau Of Land Management; JORGENSEN, CARL - Us Forest Service (FS); Rinella, Matthew - Matt

Submitted to: Forest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2014
Publication Date: 1/29/2015
Citation: Perkins, D.L., Jorgensen, C., Rinella, M.J. 2015. Verbenone decreases whitebark pine mortality throughout a mountain pine beetle outbreak. Forest Science. 61(4):747-752. http://dx.doi.org/10.5849/forsci.14-052.

Interpretive Summary: Mountain pine beetle outbreaks are killing large numbers of pine trees on millions of acres in the western U.S. The ranges, impacts and frequencies of mountain pine beetle outbreaks are increasing, perhaps due to climate change. One of the species being impacted is whitebark pine, a five-needle pine already threatened by white pine blister rust. White bark pine is a keystone species providing a variety of values, including watershed protection, and food and habitat for wildlife. Whereas protecting large numbers of trees across whitebark pine's entire range is not feasible, there is interest in protecting small numbers of trees in select locations to assist in natural and managed regeneration. One method of protecting pines involves the antiaggregation pheromone verbenone. In several studies, verbenone placed in pouches and affixed to pines increased tree survival by preventing mountain pine beetles from infesting trees at lethal densities. However, verbenone pouches are'only effective the year they are applied, and no studies have evaluated the ability of annually applied verbenone to protect whitebark pines until outbreaks end. In this study, we began applying verbenone after mountain pine beetles started killing whitebark pines and continued with annual applications for seven years until it was clear the beetle outbreak had ended. Compared to control trees, whitebark pine survival was -30% greater in verbenone-treated trees. Verbenone can be used to elevate numbers of whitebark pines surviving mountain pine beetle outbreaks. Surviving trees could prove critical to restoration efforts.

Technical Abstract: Mountain pine beetle [Dendroctonus ponderosae (Hopkins)] outbreaks are killing large numbers of pine trees on millions of hectares in the western U.S. The ranges, impacts and frequencies of mountain pine beetle outbreaks are increasing, perhaps due to climate change. One of the species being impacted is whitebark pine (Pinus albicaulis Engelm.), a five-needle pine already threatened by the exotic fungus Cronartium ribicola, which causes white pine blister rust. Whitebark pine is a keystone species providing a variety of values, including watershed protection, and food and habitat for wildlife. Whereas protecting large numbers of trees across white bark pine's entire range is not feasible, there is interest in protecting small numbers of trees in select locations to assist in natural and managed regeneration. One method of protecting pines involves the anti-aggregation pheromone verbenone. In several studies, verbenone placed in pouches and affixed to pines increased tree survival by preventing mountain pine beetles from infesting trees at lethal densities. However, verbenone pouches are only effective the year they are applied, and no studies have evaluated the ability of annually applied verbenone to protect whitebark pines until outbreaks end. In this study, we began applying verbenone after mountain pine beetles started killing whitebark pines and continued with annual applications for seven years until it was clear the beetle outbreak had ended. Compared to control trees, whitebark pine survival was ~30% greater in verbenone-treated trees. Verbenone can be used to elevate numbers of whitebark pines surviving mountain pine beetle outbreaks. Surviving trees could prove critical to restoration efforts.