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ViewAttendees 17

P-IE

10-Minute Paper

10-min: P-IE, Ecology

Impacts of mountain pine beetle, Dendroctonus ponderosae, outbreaks on lodgepole pine forests in the Intermountain West, U.S.

On-Demand
On-Demand
Following historic mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), outbreaks in the Intermountain West, U.S. from 2004-2012, we investigated resulting tree mortality and the effects on forest structure and composition. A network of 125, 0.081-ha circular plots was established in lodgepole pine, Pinus contorta, forests in Colorado, Idaho, Montana, Utah, and Wyoming. Plots were installed in 2010 and sampled annually through 2019. 5107 trees died across the network, 98.6% of which were lodgepole pine. Most of the observed tree mortality (68.8%) was attributed to D. ponderosae. The resulting mortality significantly reduced mean diameters at breast height (dbh; by 5.3%), quadratic mean diameter (by 8.6%), tree height (by 15.9%), numbers of trees (by 40.8%), basal area (by 52.9%), and stand density index (by 51.8%). Tree density significantly declined for all diameter classes (5-cm classes) except for the smallest (7.5-12.5 cm). Subalpine fir, Abies lasiocarpa, was well represented in the understory regeneration. We observed more A. lasiocarpa than P. contorta seedlings (≤0.3 m tall) in all states except Montana. An increased number of A. lasiocarpa saplings ( >0.3 m tall and < 7.6 cm dbh) contributed to the increase in the number of saplings observed across all states from 2010 to 2018. The number of snags (standing dead trees) increased substantially (by 1324.7%). Interestingly, 75.3% snags remained standing in 2019, prompting an interest in snag longevity. We modeled snag fall rates using a Cox’s proportional hazard model to estimate retention time and identify factors contributing to snag fall.