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High survival of small whitebarkpine at alpine treelineedges –and in forest interiors –after widespread mountain pine beetle outbreaks in the US Northern Rockies

Date: November 15, 2018
Presenter(s): Colin T. Maher
Description: Mountain pine beetles (Dendroctonusponderosae; MPB) are causing extensive mortality of whitebarkpine (Pinusalbicaulis) throughout the species’srange. In the highest mountains where these trees grow, they reach alpine treeline–the climatic boundary where growth forms transition from trees to shrub-like krummholz. Although treelinewhitebarkpine exist within a landscape of widespread MPB-caused mortality, these populations appear to have survived the most recent outbreaks. This observation motivated the hypothesis that stunted treelinegrowth forms escape MPB attack because their stems are too small to attract beetles, and that these habitats serve as refuges for whitebarkpine. The purpose of this research was to determine if treelineecotone populations could serve as refuges for whitebarkpine from the most recent MPB outbreaks in the US Northern Rocky Mountains, and whether these populations represent the greatest potential for future whitebarkpine population recovery. I surveyed mortality along 500 m transects at alpine treelineand other forest edges at 10 randomly selected sites in the US Northern Rocky Mountains. I found consistent mortality gradients at alpine treelines, but not at other edges. This supports the hypothesis that treelinehabitats are refuges, and that treelinewhitebarkpine may avoid MPBs because of transitions in growth form. I observed limited reproductive output at alpine treelines, but these habitats may still serve as population refuges over long time periods. However, smaller surviving whitebarkpine exist at greater density than dead ones (by ~200 per ha) throughout my study region, indicating a strong potential for these forests to recover from the recent MPB outbreaks in the short-term without a treelinerefuge.
Topic(s): Fire Effects, Ecological - Second Order, Vegetation, Wildlife, Fire & Wildlife, Invertebrates, Mountain pine beetles
Ecosystem(s): None
Type: Webinar
NRFSN number: 18763
Record updated: Dec 12, 2018