| Limber Pine Pinus flexilis |
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|---|---|
| Limber pine in the Craters of the Moon National Monument, Idaho | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Pinophyta |
| Class: | Pinopsida |
| Order: | Pinales |
| Family: | Pinaceae |
| Genus: | Pinus |
| Subgenus: | Strobus |
| Species: | P. flexilis |
| Binomial name | |
| Pinus flexilis E.James |
|
The Limber Pine, Pinus flexilis, is a species of pine tree-the family Pinaceae that occurs in the mountains of the Western United States, Mexico, and Canada. It is also called Southwestern White Pine and Rocky Mountain White Pine. A Limber Pine in Eagle Cap Wilderness, Oregon has been documented as over 2000 years old, and another one was confirmed at 1140 years old.[1]
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Limber Pine - Pinus flexilis is specifically found in the subalpine areas of the Rocky Mountains from southwest Alberta Canada south through Colorado and New Mexico into the northern states of Mexico; from mountains in the eastern Pacific Northwest states through the Great Basin states of Nevada and Utah. It is also found in California: in the Eastern Sierra Nevadas; the eastern California White Mountains; and the Southern California San Bernardino Mountains, San Gabriel Mountains, and San Jacinto Mountains of the Transverse Ranges; and a small disjunct population in the Black Hills in South Dakota.[2][3]
Pinus flexilis is typically a high-elevation pine, often marking the tree line either on its own, or with Whitebark Pine (Pinus albicaulis), either of the Bristlecone pines, or Lodgepole Pine (Pinus contorta). In favourable conditions, it makes a tree to 20-metre (66 ft), rarely 25-metre (82 ft) tall. However, on exposed treeline sites, mature trees are much smaller, reaching heights of only 5-metre (16 ft) - 10-metre (33 ft).[2] In steeply-sloping, rocky and windswept terrain in the Rocky Mountains of southern Alberta, limber pine is even more stunted, occurring in old stands where mature trees are consistently less than 3m in height.[4]
In Arizona, New Mexico, and Texas, populations of the Limber Pine often known as Southwestern White Pine, differ from the populations farther north. These are sometimes treated as a variety, Pinus flexilis var. reflexa, but more often as a distinct species, either "accurately" under the name Pinus reflexa, or erroneously through confusion with the Mexican Chihuahua White Pine under the name Pinus strobiformis, which correctly applies to the Chihuahua White Pine.
The 'Southwestern White Pine' differs from typical Limber Pine in being a larger tree, to 25-metre (82 ft) - 35-metre (115 ft) tall, with longer needles, 6-centimetre (2.4 in) - 11-centimetre (4.3 in) long, which have strongly white stomatal bands on the inner faces of the needles (inconspicuous in the type), and are slightly serrated towards the tips of the needles.
The cones are also larger, typically 10-centimetre (3.9 in) - 20-centimetre (7.9 in) long. 'Southwestern White Pine' differs from true Mexican Pinus strobiformis in that the needles are not fully serrated, and the cones being smaller 15-centimetre (5.9 in) - 25-centimetre (9.8 in) in P. strobiformis), the cone scales shorter and the seeds smaller.
It is possible that Pinus reflexa is a natural hybrid between Pinus flexilis and Pinus strobiformis. Type localities of the three taxa are:
Limber Pine - Pinus flexilis 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 the bristlecone pines, which share five needles per fascicle but have a semi-persistent sheath.
Distinguishing Limber Pine from the related Whitebark Pine, also a white pine, is very much more difficult, and can only easily be done by the cones. In Limber Pine, the cones are 6-centimetre (2.4 in) - 12-centimetre (4.7 in) long where the species overlap, green when immature, and open to release the seeds; the scales are not fragile. In Whitebark Pine, the cones are 4-centimetre (1.6 in) - 7-centimetre (2.8 in) 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.[5] A useful clue resulting is that Whitebark Pines almost never have intact old cones lying under them, whereas Limber Pines usually do.
In the absence of cones, Limber Pine can also be hard to tell from Western White Pine where they occur together in the northern Rockies and the Sierra Nevada east slope. The most useful clue here is that Limber Pine needles are entire (smooth when rubbed gently in both directions), whereas Western White Pine needles are finely serrated (feeling rough when rubbed gently from tip to base). Limber Pine needles are also usually shorter, 4-centimetre (1.6 in) - 7-centimetre (2.8 in) long, to Western White Pine's 5-centimetre (2.0 in) - 10-centimetre (3.9 in) (though note the overlap).
Unfortunately, Limber Pine is afflicted with White Pine Blister Rust (Cronartium ribicola), a fungus that was introduced accidentally from Europe. Limber Pine mortality is high in many areas throughout its range, except Arizona, where it has not yet been found. 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 Limber 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.
The popular cultivar Pinus flexilis 'Vanderwolf's Pyramid' is widely available as an ornamental tree for gardens. 'Vanderwolf's Pyramid' derives from Pinus reflexa, though it is usually listed in nursery catalogs under Pinus flexilis.
Limber Pine is an important source of food for several species, including Red Squirrels and Clark's Nutcrackers. American Black Bears may raid squirrel caches for Limber Pine nuts. Squirrels, Northern Flickers, and Mountain Bluebirds often nest in the trees.