NOAA/WDS Paleoclimatology - Kichas - Gallatin Crest - PIAL - ITRDB MT180

Whitebark pine (Pinus albicaulis, WBP) is an important high-elevation conifer in the Western US that was listed as “threatened” under the Endangered Species Act in 2023. Consequently, land managers are tasked with ensuring the long-term viability of WBP populations through conservation and restoration efforts. The effects of mountain pine beetle (Dendroctonus ponderosae, MPB) outbreaks on WBP dynamics are poorly understood, especially for smaller diameter trees that typically escape attack due to their small size, allowing for persistence in the understory through outbreak events. Here, we assess growth responses for 10-25 cm diameter WBP trees growing in areas within the Greater Yellowstone Ecosystem that experienced significant overstory mortality (impacted by MPB) and locations that experienced little to no mortality (unimpacted by MPB) during a MPB outbreak spanning from the 1970s through the early 1980s (peaking in 1981). In the 31 years following the outbreak, surviving WBP in the impacted units experienced a significant growth release (61% increase in basal area increment; cm2 year-1) compared to WBP in the unimpacted units (8% increase in basal area increment). Additionally, in the post-outbreak period we found strong, positive relationships between WBP growth and minimum temperature in the impacted units only, suggesting that the outbreak may have altered canopy structure in ways that increased growth potential for surviving WBP. Collectively, our findings suggest that the presence of smaller diameter trees in WBP forests can offer resilience to beetle impacts and emphasizes the importance of maintaining multi-aged forest structures to buffer outbreak effects.