The Whitebark Pine (Pinus albicaulis; family Pinaceae) is a species of pine tree that 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 (including the Greater Yellowstone Ecosystem). The Whitebark Pine is typically the highest-elevation pine tree of these mountains, marking the tree-line. Thus, they are often found as krummholz, trees dwarfed by exposure and growing close to the ground. In more favourable conditions, it makes a tree to 20 m, rarely 27 m tall.

Whitebark Pine is a member of the white pine group, Pinus subgenus Strobus, and like all members of that group, the leaves ('needles') are in fascicles (bundles) of five, with a deciduous sheath. This distinguishes it from the Lodgepole Pine, with two needles per fascicle, and Ponderosa Pine and Jeffrey Pine, which both have three per fascicle; these three all also have a persistent sheath at the base of each fascicle.

Distinguishing Whitebark Pine from the related Limber Pine, also a white pine, is very much more difficult, and can only easily be done by the cones. In Whitebark Pine, the cones are 4-7 cm long, dark purple when immature, and do not open on drying, but are fragile and are pulled apart by birds (see below) to release the seeds. In Limber Pine, the cones are 6-12 cm long, green when immature, and open to release the seeds; the scales are not fragile. A useful clue resulting is that Whitebark Pines almost never have intact old cones lying under them, whereas Limber Pines usually do.

Whitebark Pine can also be hard to tell from Western White Pine in the absence of cones. The most useful clue here is that 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 cm long, to Western White Pine's 5-10 cm (though note the overlap).

The Whitebark Pine is an important source of food for several species, including most importantly the Clark's Nutcracker, the major seed disperser of the pine. Clark's Nutcrackers cache huge numbers of Whitebark Pine seeds (up to 100,000 seeds per bird each year) in small, widely scattered caches usually on bare ground: ideal situations for regeneration of the pine, for the many caches which never get used. One consequence of this is that Whitebark Pines often grow as clumps of several trees, originating from a single cache of 5-10 seeds; this assists tree survival at tree-line, with the cluster of trees providing shelter for each other where a single tree might not survive.

Douglas Squirrels also take many seeds, and Grizzly Bears and American Black Bears often raid squirrel caches for the Whitebark Pine nuts. Squirrels, Northern Flickers, and Mountain Bluebirds often nest in the Whitebark Pines.

Unfortunately, Whitebark Pines in Washington, Idaho, Montana, British Columbia, and Alberta are afflicted with White Pine Blister Rust (Cronartium ribicola), a fungus that was introduced from Europe. Whitebark Pine mortality in some areas is exceeding 60%. The blister rust has also devastated the commercially valuable Western White Pine in these areas. However, there is no known way of controlling the blister rust in existing trees. Research is under way, locating and breeding from the occasional naturally resistant Whitebark Pines, and by studying the resistance mechanisms of the European and Asian white pines (e.g. Swiss Pine, Macedonian Pine), which are strongly resistant to the disease.

Reference

• R. M. Lanner, 1996. Made for each other: a symbiosys of birds and pines. OUP. ISBN 0-19-508903-0

External links

• Pinus albicaulis cone pic (scroll to foot of page) (http://www.pinetum.org/cones/PNStrobus.htm)
  
• Gymnosperm Database - Pinus albicaulis (http://www.botanik.uni-bonn.de/conifers/pi/pin/albicaulis.htm)
• The Whitebark Pine (at USGS) (http://biology.usgs.gov/s+t/SNT/noframe/wm147.htm)
• Whitebark Pine Communities (at USGS) (http://www.nrmsc.usgs.gov/research/whitebar.htm)
• Whitebark Pine Ecosystem Foundation (http://www.whitebarkfound.org)