Whitebark pine (Pinus albicaulis) growth and defense in response to mountain pine beetle outbreaks

Abstract

Whitebark pine (WBP; Pinus albicaulis) is a critical keystone forest species of U.S. Northern Rocky Mountain subalpine ecosystems (Tomback et al. 2001). There is growing concern that WBP may be largely extirpated from its current habitat over the next century due to cumulative impacts of climate change, insect-related mortality, changing fire regimes, increased competition from shade-tolerant species, and the invasive exotic pathogen white pine blister rust (Cronartium ribicola). While insects, fire, disease, and drought have contributed to recent mortality of WBP, these processes are also thought to play an important role in the long–term establishment and persistence of Northern Rocky Mountain WBP forests. Historical records detailing patterns and characteristics of disturbance that promote or inhibit WBP establishment and persistence are poorly lacking, highlighting a critical research need. Within conifers, resin-based defenses (direct expulsion of beetles from tree phloem/cambium via resin flow through ducts) have long been recognized as the primary mechanism by which trees respond to attack by bark beetles and pathogens. Resin ducts are permanent anatomical features within the secondary xylem and have been shown to correspond with resin flow, such that greater total area of resin ducts facilitates increased production, storage, and mobilization of oleoresin to sites of wounding. As resin ducts are produced regularly (typically every year to every few years), they can be measured, along with tree rings, to assess how trees allocate resources between growth and defense over time. Several researchers have linked physical properties of resin ducts to survivorship during periods of increased beetle activity (see Kichas et al. 2020 for key references).

Citation

Kichas, Nickolas E.; Hood, Sharon M.; Pederson, Gregory T.; Everett, Richard G.; McWethy, David B. 2020. Whitebark pine (Pinus albicaulis) growth and defense in response to mountain pine beetle outbreaks. Nutcracker Notes. 38: 15-19.