Whitebark Pine

Past climate change has shaped the biogeography of whitebark pine and, hence, genetic relationships and potential adaptive traits. Since the last glacial maximum, whitebark pine has apparently responded to the warming climate after the last glacial maximum by colonizing new habitat opened up by receding glaciers of the Canadian Rocky Mountains and the northern Cascades. Holocene expansion into the northern Cascade Mountains likely originated from source populations to the south and east of the north Cascades, based on the mtDNA at the contact zone (Richardson and others 2002). In contrast, a wider distribution of whitebark pine in more southern latitudes during the last glacial maximum was probably constricted to higher elevations due to subsequent Holocene warming. This constriction in suitable habitat appears particularly dramatic in northern Nevada, where whitebark pine currently persists only on the highest mountaintops.

Population genetics of whitebark pine have identified distinct regional metapopulations occupying the Pacific Northwest, (i.e., northern Rockies and Cascade Mountains), the greater Yellowstone region, and the Sierra Nevada. Other populations in the Great Basin and central Oregon have not been analyzed with mtDNA or cpSSR markers. However, allozyme analyses have shown distinct genetic structure among the Great Basin whitebark pine populations (Yandell 1992). Further studies to characterize genetic diversity and structure of whitebark pine in the State of Washington and Oregon are in progress (Personal communication. C. Aubry [Year unknown] Area Geneticist, Olympia National Forest, 1835 Black Lake Blvd. Suite A, Olympia, WA 98512), and studies are assessing rangewide and regionwide adaptive traits in whitebark pine (Bower and Aitken 2006). These studies and population genetic analyses are essential to determine appropriate genetic conservation efforts and proactive management that consider predicted climate change.

The contemporary climate space predicted using the plant-climate model is extremely precise for the distribution of whitebark pine. This precision has also been demonstrated with other western plant species (Rehfeldt and others 2006). The predicted suitable climate space for whitebark pine shows a dramatic reduction in the year 2030. At the highest risks are populations that currently only exist on mountaintops, where projected suitable climate space will be entirely lost from the region. Loss of local whitebark pine populations is predicted to occur throughout the Oregon Cascades and mountaintops of northern Nevada, and further result in disjunct populations in the Sierra Nevada that will persist only at the highest elevations. These populations that face the highest risk of extirpation from predicted climate change and the white pine blister rust fungus should take priority for seed bank collections. Besides the Sierra Nevada, the plant-climate model predicts four major regions where climate space remains in the Western United States. These regions include the highest mountain ranges: the northern Cascades, Glacier National Park, south-central mountain ranges in Idaho, and the greater Yellowstone region. These regions that contain suitable climate space in 2030 predictions should be considered as priority regions for restoration efforts.