Whitebark pine (WBP; Pinus albicaulis) is a critical keystone species of U.S. Northern Rocky Mountain subalpine ecosystems. There is growing concern that WBP may be eliminated 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 disturbance events are also thought to play an important role in the long-term establishment and persistence of WBP forests. Historical records detailing patterns and characteristics of disturbance that promote or inhibit WBP establishment and persistence are lacking.
Within conifers, resin-based defenses (i.e., 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. Greater total resin duct area facilitates increased production, storage, and mobilization of resin 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 tree survival during periods of increased bark beetle activity (see Kichas et al. 2020 for key references).
In this study, we evaluated whether diameter growth and resin duct characteristics differed between live trees and dead trees during recent disturbance events (e.g., mountain pine beetle outbreaks, drought, fire). Evaluating relationships between resin duct structures, resin production, and disturbance can provide valuable insight into how these trees will respond to stressors that are projected to increasingly impact whitebark pine.