Western White Pine

Like whitebark pine, western white pine populations were also shaped by past climate change. This process created genetic structure with similarities to whitebark pine: a large Pacific Northwest metapopulation with partitions in southern Oregon and northern California. This population structure is also supported by an earlier study of isozyme markers (Steinhoff and others 1983). In addition, similar findings were reported in a study of adaptive traits for western white pine, showing a relationship between latitude and shoot elongation with a transition zone in southern Oregon (Rehfeldt and others 1984).

Again, the bioclimatic model predicted an excellent fit to the known distribution of western white pine. However, predicted 2030 climate space for western white pine shows a stark contrast to whitebark pine. The predicted increase in climate space is evident as an expansion in the northern Rocky Mountains that apparently relates to a slight increase in moisture. In the Sierra Nevada and Siskiyou Mountains, predicted climate space in 2030 does not show expansion. In these areas, moisture levels are predicted to increase more dramatically relative to the Pacific Northwest, and predicted climate becomes less suitable for western white pine, possibly due to increased competition. Whereas losses of genetic diversity seem relatively small compared to whitebark pine, some areas of western white pine may be at risk. Reductions in the abundance or extirpation of small isolated populations are conceivable for the Siskiyou Mountains and other areas of northern California where the western white pine populations exhibit a unique and diverse genetic background. Such populations should be considered as a priority for genetic conservation efforts.