Whitebark Pine

Population Genetics

Analysis of mtDNA reveals three haplotypes that are discretely partitioned among regions with two introgression zones. One introgression zone apparently occurs across a broad area in central Idaho, and another introgression zone occurs across a narrow area in the northern Cascades near Mount Rainer, Washington. The introgression of mtDNA haplotypes in the northern Cascades has been proposed to have resulted from the colonization of previously glaciated habitat during Holocene warming (Richardson and others 2002).

Fig. 1 - Whitebark Pine
Distribution.

Analysis of pollen gene flow using cpSSRs reveals broader population boundaries that include mtDNA introgression zones. These data circumscribe three metapopulations: the Sierra Nevada Mountains, the Yellowstone region, and a large Pacific Northwest region that includes the northern Rocky Mountains and the Cascades (Figure 1-A). Private alleles were typically found at low frequency within each region; however, one notable exception was the Sierra Nevada metapopulation that had a private allele at high frequency. Genetic diversity has been described as moderately high for cpSSR markers (Richardson and others 2002) to moderately low using allozyme analysis (reviewed in Bruederle and others 2001). Furthermore, genetic characterization of isolated populations in southern Oregon, northern California, and Nevada are still needed to assess genetic conservation efforts in these areas.

Plant-Climate Modeling

The contemporary plant-climate model for whitebark pine fits its present distribution with remarkable precision. Comparisons between ground-truthed whitebark pine locations and predicted areas of suitable habitat showed an overall error rate of only 2.47 percent (Figure 1-A). The mapped predictions for the occurrence of whitebark pine were more accurate than Little’s (1971) published range maps (Warwell and others 2006). Based on two GCMs (Hadley and Canadian Centre for Climate Change), the projected climatic space for whitebark pine in ca. 2030 shows a dramatic change in comparison with the contemporary prediction. An estimated 70 percent of the current climate space for whitebark pine will be lost by 2030. Most of predicted loss occurs in the southern latitudes of the whitebark pine range, including the Oregon Cascades, Siskiyou, and northern Nevada mountain ranges, where current suitable habitats are limited to mountaintops in many locations (Figure 1-B). The elevation of suitable climate space is also expected to rise 330 m, thereby leaving only the Sierra Nevada Mountains as a potential refuge with suitable climate space below 40º N latitude. In contrast, the model does predict suitable climate space will occur in central Colorado, which may represent a fundamental climate niche for whitebark pine. In the northern Rockies and Cascades, whitebark pine climate space is predicted to persist only among the highest elevations found in Yellowstone, south-central Idaho, Glacier National Park, and the northern Cascades. Areas north of 50º N will also likely fit climatic space for whitebark pine, but these areas fell outside of the geographic window and are not included in the analyses.