|A stand of whitebark pines at Crater Lake National Park, Oregon|
|Natural range of Pinus albicaulis|
Pinus albicaulis, with many common names including whitebark pine, white pine, pitch pine, scrub pine, and creeping pine, occurs in the mountains of the Western United States and Canada, specifically the subalpine areas of the Sierra Nevada, the Cascade Range, the Pacific Coast Ranges, and the Rocky Mountains from Wyoming through the Continental Ranges. It shares the common name creeping pine with several other "creeping pine" plants.
The whitebark pine is typically the highest-elevation pine tree of these mountains, marking the tree line. Thus, it is often found as krummholz, trees dwarfed by exposure and growing close to the ground. In more favourable conditions, trees may grow to 20 meters (66 ft) in height, although some can reach up to 27 meters (89 ft).
Whitebark pine (Pinus albicaulis) is a member of the white pine group, Pinus subgenus Strobus, section Strobus and like all members of that group, the leaves ('needles') are in fascicles (bundles) of five, with a deciduous sheath. This distinguishes whitebark pine and relatives from the lodgepole pine (Pinus contorta), with two needles per fascicle, and Ponderosa pine (Pinus ponderosa) and Jeffrey pine (Pinus jeffreyi), which both have three per fascicle; these three all also have a persistent sheath at the base of each fascicle.
Distinguishing whitebark pine (Pinus albicaulis), from the related limber pine (Pinus flexilis), also a "white pine", is much more difficult, and needs seed or pollen cones. In Pinus albicaulis, the cones are 4–7 centimeters (1.6–2.8 in) long, dark purple when immature, and do not open on drying, but the scales easily break when they are removed by Clark's Nutcracker (see below) to harvest the seeds; rarely are there intact old cones under them. Its pollen cones are scarlet.
In Pinus flexilis, the cones are 6–12 centimeters (2.4–4.7 in) long, green when immature, and open to release the seeds; the scales are not fragile. Usually there are intact old cones under them. Their pollen cones are yellow.
Whitebark pine (Pinus albicaulis) can also be hard to distinguish from western white pine (Pinus monticola) in the absence of cones. However, whitebark pine needles are entire (smooth when rubbed gently in either direction), whereas western white pine needles are finely serrated (feeling rough when rubbed gently from tip to base). Whitebark pine needles are also usually shorter, 4–7 centimeters (1.6–2.8 in) long, overlapping in size with the larger 5–10 centimeters (2.0–3.9 in) needles of the western white pine.
Source of food
The whitebark pine is an important source of food for many granivorous birds and small mammals, including most importantly the Clark's Nutcracker, the major seed disperser of the pine. Clark's Nutcrackers each cache about 30,000 to 100,000 each year in small, widely scattered caches usually under 2 to 3 cm of soil or gravelly substrate. Nutcrackers retrieve these seed caches during times of food scarcity and to feed their young. Cache sites selected by nutcrackers are often favorable for germination of seeds and survival of seedlings. Those caches not retrieved by time snow melts contribute to forest regeneration. Consequently, whitebark pine often grows in clumps of several trees, originating from a single cache of 2–15 or more seeds. Douglas Squirrels cut down and store whitebark pine cones in their middens. Grizzly Bears and American Black Bears often raid squirrel middens for whitebark pine seeds, an important pre-hibernation food. Squirrels, Northern Flickers, and Mountain Bluebirds often nest in whitebark pines, and elk and Blue Grouse use whitebark pine communities as summer habitat.
A study in the mid-2000s showed whitebark pine had declined by 41 percent in the Western Cascades, due to two threats: white pine blister rust and mountain pine beetles. Whitebark deaths in North Cascades National Park doubled from 2006 to 2011.
White pine blister rust
Many stands of Pinus albicaulis nearly range-wide are infected with white pine blister rust (Cronartium ribicola), a fungal disease that was introduced from Europe. In the northern Rocky Mountains of the U.S., whitebark pine mortality in some areas exceeds 90%, where the disease infests 143,000 acres (580 km2). Cronartium ribicola occurs in whitebark pine to the northern limits of the species in the coastal ranges of British Columbia and the Canadian Rocky Mountains. The blister rust has also devastated the commercially-valuable western white pine in these areas, and made serious inroads in limber pine (Pinus flexilis) populations as well. Nearly 80 percent of Whitebark pines in Mount Rainier National Park are infected with blister rust.
There is currently no way to stop the spread and effects of blister rust. However, a small number of trees (fewer than 5%) in most populations harbor genetic resistance to blister rust. There have been some restoration efforts by the U.S. Forest Service, Bureau of Land Management, and National Park Service in the northern Rocky Mountains. Restoration efforts involve harvesting cones from potentially and known resistant whitebark pines, growing seedlings, and outplanting seedlings in suitable sites.
In California, where the blister rust is far less severe, whitebark pine are still fairly common in the High Sierras.
Mountain pine beetle
There are widespread outbreaks of mountain pine beetle in the western U.S. and Canada. Since 2000, the climate at high elevations has been warm 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, are expanses of dead gray whitebarks. This warming has been attributed by some researchers to global warming.
In 2007, the U.S. Fish and Wildlife Service estimated the beetles killed whitebark pines across half a million acres in the West, while in 2009, beetles were estimated to have killed trees on 800,000 acres (320,000 ha), the most since record-keeping began. The pine beetle upsurge has killed nearly 750,000 whitebark pines in the Greater Yellowstone Ecosystem alone.[when?]
Fire suppression has led to slow population declines over the last century by altering the health and composition dynamics of stands without the fire ecology balancing their habitat and suppressing insect-disease threats. 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.
On July 18, 2011, the U.S. Fish and Wildlife Service reported that the whitebark pine needed protection and that, without it, the tree would soon be extinct. However, the agency announced it would neither be able to list the tree as endangered nor protect the organism, as it lacked both the necessary staff and funding to do so. In June 2012, the Canadian federal government declared whitebark pine endangered in accordance with the Species at Risk Act. As such, it is the first federal endangered tree in Western Canada.
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- Logan, J.A.; Regniere, J.; Powell, J.A. (2003). "Assessing the Impacts of Global Warming on Forest Pest Dynamics". Frontiers in Ecology and the Environment 1 (3): 130–137. doi:10.1890/1540-9295(2003)001[0130:ATIOGW]2.0.CO;2.
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|Wikimedia Commons has media related to:|
- Pinus albicaulis from USDA Plants Profile
- Pinus albicaulis from Jepson Manual Treatment
- Pinus albicaulis from Gymnosperm Database
- Pinus albicaulis from Flora of North America
- Pinus albicaulis – U.C. Photos Gallery
- "Whitebark Pine". United States Geological Survey. Archived from the original on 2007-07-14.
- Whitebark Pine Communities from the United States Geological Survey
- Official website of the Whitebark Foundation
- High Elevation White Pine – Pinus albicaulis from the USDA Forest Service's Rocky Mountain Research Station