Adaptive variation in Pinus aristata, Rocky Mountain Bristlecone Pine: Application to conservation of a species challenged by climate change and a non-native disease

Anna W. Schoettle, Rocky Mountain Research Station, USDA Forest Service, Ft. Collins, CO, Betsy Goodrich, Forest Health Protection, USDA Forest Service, Wenatchee, WA and Detlev R. Vogler, Institute of Forest Genetics, USDA FS, Pacific Southwest Research Station, Placerville, CA

Background/Question/Methods
Pinus aristata Engelm., Rocky Mountain bristlecone pine, has a narrow geographic and elevational distribution and occurs in disjunct mountain-top populations throughout Colorado and New Mexico in its core range. The species’ unique aesthetic and ecological traits combined with the threats of the non-native disease white pine blister rust (WPBR), climate change in high elevation systems, and an outbreak of a native bark beetle make P. aristata of conservation interest. The combination of low genetic diversity (neutral markers), moderate population isolation, and a protracted regeneration dynamic suggest that populations are at risk for extirpation by novel stresses such as WPBR and climate change. Little is known about the species adaptive variation in growth and resistance to WPBR. We used common garden studies to explore the geographic distribution of adaptive traits for this species to help guide the development of conservation strategies and the evaluation of risk among geographic regions. Two common gardens studies were installed with common seed sources. Pinus aristata seeds were collected from 200 individual trees from 11 sites throughout Colorado and sown in two greenhouse common gardens in 2002: one garden focused on growth and phenology of two-year-old seedlings and the other on the response of seedlings to artificial inoculation with the pathogen that causes WPBR to infer genetic resistance to the disease.
Results/Conclusions
Genetic differentiation among sites was clear for growth phenology but weak for duration of growth. Some growth traits were correlated with latitude but not elevation of the source material. Source elevation explained variation in mid-winter cold hardiness. Likewise, response to artificial inoculation with Cronartium ribicola, the non-native pathogen that causes WPBR, also varied with seed source. The patterns of variation among families and source sites were similar between the two common gardens with evidence of correlations between growth and disease progression. Interestingly, preliminary data suggested an interaction such that the relative autumn cold-hardiness among sources was altered by pathogen inoculation. Resistance to WPBR is a critical adaptive trait for bristlecone survival in the future as the pathogen continues to spread through the pine’s distribution. The results of the two common gardens provides information on the integrated patterns of disease resistance and growth traits to guide seed source selections for conservation planting projects and to assess risk among geographic regions.