Skip to main content
Author(s):
Colin T. Maher, Constance I. Millar, David L.R. Affleck, Robert E. Keane, Anna Sala, Claudine Tobalske, Andrew J. Larson, Cara R. Nelson
Year Published:

Cataloging Information

Topic(s):
Fire Ecology
Fire Effects

NRFSN number: 22978
Record updated:

Warming‐induced mountain pine beetle (Dendroctonus ponderosae; MPB) outbreaks have caused extensive mortality of whitebark pine (Pinus albicaulis; WBP) throughout the species’ range. In the highest mountains where WBP occur, they cross alpine treeline ecotones (ATEs) where growth forms transition from trees to shrub‐like krummholz, some of which survived recent MPB outbreaks. This observation motivated the hypothesis that ATEs are refugia for WBP because krummholz growth forms escape MPB attack and have the potential to produce viable seed. To test this hypothesis, we surveyed WBP mortality along transects from the ATE edge (locally highest krummholz WBP) downslope into the forest and, to distinguish if survival mechanisms are unique to ATEs, across other forest ecotones (OFEs) from the edge of WBP occurrence into the forest. We replicated this design at 10 randomly selected sites in the U.S. Northern Rocky Mountains. We also surveyed reproduction in a subset of ATE sites. Mortality was nearly absent in upper ATEs (mean ± SE percent dead across all sites of 0.03% ± 0.03% 0–100 m from the edge and 14.1% ± 1.7% 100–500 m from the edge) but was above 20% along OFEs (21.4 ± 5.2% 0–100 m and 32.4 ± 2.7% 100–500 m from the edge). We observed lower reproduction in upper ATEs (16 ± 9.9 cones/ha and 12.9 ± 5.3 viable seeds/cone 0–100 m from the edge) compared to forests below (317.1 ± 64.4 cones/ha and 32.5 ± 2.5 viable seeds/cone 100–500 m from the edge). Uniquely high WBP survival supports the hypothesis that ATEs serve as refugia because krummholz growth forms escape MPB attack. However, low reproduction suggests ATE refugia function over longer time periods. Beyond our WBP system, we propose that plant populations in marginal environments are candidate refugia if distinct phenotypes result in reduced disturbance impacts.

Citation

Maher CT, Millar CI, Affleck DLR, Keane RE, Sala A, Tobalske C, Larson AJ, and Nelson CR. 2020. Alpine treeline ecotones are potential refugia for a montane pine species threatened by bark beetle outbreaks. Ecological Applications 31 (3): e2274. https://doi.org/10.1002/eap.2274

Access this Document

Treesearch

publication access with no paywall

Check to see if this document is available for free in the USDA Forest Service Treesearch collection of publications. The collection includes peer reviewed publications in scientific journals, books, conference proceedings, and reports produced by Forest Service employees, as well as science synthesis publications and other products from Forest Service Research Stations.