AUTHOR=Six Diana L. , Trowbridge Amy , Howe Michael , Perkins Dana , Berglund Erika , Brown Peter , Hicke Jeffrey A. , Balasubramanian Ganesh 

TITLE=Growth, Chemistry, and Genetic Profiles of Whitebark Pine Forests Affected by Climate-Driven Mountain Pine Beetle Outbreaks

JOURNAL=Frontiers in Forests and Global Change

VOLUME=Volume 4 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2021.671510

DOI=10.3389/ffgc.2021.671510

ISSN=2624-893X

ABSTRACT=We investigated the possibility that climate change-driven Dendroctonus ponderosae outbreaks in semi-naïve Pinus albicaulis resulted in rapid natural selection for trees with genotypes and phenotypes associated with survival. In particular, we focused on whether survivors were genetically different and had distinct secondary chemical profiles. We also investigated how growth rate and climate sensitivity influence tree vigor, defense, and susceptibility, and varied between beetle-killed and surviving trees and estimated genetic diversity. Dendroctonus ponderosae predominantly kills large diameter trees; therefore, we predicted that large surviving trees would have distinctive genetic profiles and, due to bottlenecking and drift, survivors would have lower genetic diversity than the abundant smaller mature trees that escaped predation. We found survivors were indeed genetically distinct, but, contrary to expectations, smaller trees had lower diversity. This suggests that while beetles select for trees with particular genotypes, other factors are also driving population genetic sub-structuring. Individual tree terpene profiles were diverse and varied by population but showed no clear relationship to survivorship. Two groups of trees with divergent sensitivities to climate were observed in each population, but neither was a clear indicator of survivorship or susceptibility to beetles. Growth rate was the best predictor of survivorship with survivors growing significantly slower than beetle-killed trees over the 55-year period leading up to the outbreak. Overall, our results suggest that P. albicaulis forests show considerable local adaptation and within-population genetic sub-structuring and that they contain complex mosaics of adaptive potentials to a variety of stressors including D. ponderosae. To protect the ability of this tree to adapt to increasing pressure from beetles, blister rust, and climate change, a top priority should be the maintenance of standing genetic diversity and adaptive shifts in allele frequencies.