thumb|Pinus albicaulis is the only type of tree on the summit of [[Pywiack Dome in Yosemite National Park]]
Pinus albicaulis, known by the common names whitebark pine, white bark pine, white pine, pitch pine, scrub pine, and creeping pine, is a conifer tree native to the mountains of the western United States and Canada, specifically subalpine areas of the Sierra Nevada, Cascade Range, Pacific Coast Ranges, Rocky Mountains, and Ruby Mountains. It shares the common name "creeping pine" with several other plants.
The whitebark pine is typically the highest-elevation pine tree found in these mountain ranges and often marks the tree line. Thus, it is often found as krummholz, trees growing close to the ground that have been dwarfed by exposure. In more favorable conditions, the trees may grow to in height.
Identification
right|thumb|upright|Pinus albicaulis leaves are in fascicles (bundles) of five, and the cone is dark purple when immature ([[Mount Rainier National Park)]]
Whitebark pine is a member of the white pine group, the Pinus subgenus Strobus, and the section Strobus; like all members of this group, the leaves (needles) are in fascicles (bundles) of five with a deciduous sheath. This distinguishes whitebark pine and its relatives from the lodgepole pine (Pinus contorta), with two needles per fascicle, as well as the ponderosa pine (Pinus ponderosa) and Jeffrey pine (Pinus jeffreyi), which both have three needles per fascicle; all three of these species also have a persistent sheath at the base of each fascicle. Whitebark pine owes its name to the light gray bark of its young specimens.
In Pinus flexilis, the cones are long, green when immature, and open to release the seeds; the scales are not fragile. Their pollen cones are yellow, and there are usually intact old cones found beneath them.
Whitebark pine can also be hard to distinguish from the western white pine (Pinus monticola) in the absence of cones. However, whitebark pine needles are yellow-green
Threats
The whitebark pine has been classified as endangered by the IUCN.
Mountain pine beetle
Unusually large outbreaks of mountain pine beetle (Dendroctonus ponderosae), a species of bark beetle native to western North America, have also contributed significantly to the widespread destruction of whitebark pine stands. The beetles both lay their eggs and introduce pathogenic fungi into their host trees, which include many other species of pine, and the combination of larval feeding and fungal colonization is typically sufficient to kill old or unhealthy trees. However, the beetles have recently expanded their attacks to younger, healthier trees as well as older trees, and climate change has been implicated as the primary culprit. Since 2000, the climate at high elevations has warmed enough for the beetles to reproduce within whitebark pine, often completing their life cycle within one year and enabling their populations to grow exponentially. Entire forest vistas, like that at Avalanche Ridge near Yellowstone National Park's east gate, have become expanses of dead gray whitebarks. Scientists have attributed the recent warming trend to anthropogenic global warming.
In 2007, the U.S. Fish and Wildlife Service estimated that beetles had killed whitebark pines across in the West, while in 2009, beetles were estimated to have killed trees on , the most since record-keeping began. In the absence of low-level wildfire cycles, whitebark pines in these stands are replaced by more shade-tolerant, fire-intolerant species such as subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii). In addition, senescent and blister rust-infected pine trees are not destroyed by natural periodic ground fires, further diminishing the whitebark pine forest's vitality and survival.
Protective efforts
In 2012 the Canadian federal government declared whitebark pine endangered in accordance with the Species at Risk Act. Accordingly, it became the first federally listed endangered tree in western Canada. In 2022 the U.S. Fish & Wildlife Service also acted. It listed whitebark pine in the lowest category of vulnerability: "threatened." Four distinct threats were described, beginning with white pine blister rust as "the primary stressor." Mountain pine beetle, altered fire regimes, and "the effects of climate change" add to the challenges. This listing marks the first occasion in which a tree regarded as ecologically important over a vast range in the United States is acknowledged as vulnerable to extinction.
In response to the ongoing decline of the tree throughout its range, the Whitebark Pine Ecosystem Foundation was formed. Their mission is to raise awareness and promote conservation by sponsoring restoration projects, publishing a newsletter called "Nutcracker Notes", and hosting an annual science and management workshop for anyone interested in whitebark pine. This U.S. group collaborates closely with the Whitebark Pine Ecosystem Foundation of Canada.
Uses
thumb|upright|Whitebark pine seeds
Interior Salish peoples harvested seeds from this tree's cones for food. They were roasted, made into porridge, and mixed with dry berries.