Pinus flexilis

Its pliant branches gives it the common name "limber" and specific epithet flexilis. Its needles are about long and a dark, blueish green. Its bark is heavily creased and dark grey. Its pale wood is lightweight and soft. 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 favorable conditions, it makes a tree to , rarely tall. On exposed tree line sites, mature trees are much smaller, reaching heights of only . 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 in height. One of the world's oldest living limber pine trees grows on the banks of the upper North Saskatchewan River at Whirlpool Point in Alberta. Recent measurements give a maximum girth of 185". In 1986, a core sample 10 cm was retrieved by two researchers who counted 400 rings. Extrapolating this data gives an age close to 3,000 years. Similar species 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, A useful clue is that whitebark pines almost never have intact old cones lying under them, whereas limber pines usually do. Pinus monticola In the absence of cones, limber pine can also be hard to tell from Western white pine (P. monticola) 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, long, while western white pine needles are , although these ranges overlap. == Distribution ==

The largest part of the limber pine's range is in the Rocky Mountains, from southwest Alberta and in the Black Hills of South Dakota. It is found at a wide range of altitudes depending on the latitude, from . In the northern half of its range, it grows in the montane zone near the lower tree line; in the middle of its range between the 45th and 40th parallels, it grows on windswept sites in the montane and subalpine zones; and in the southern part of its range, it grows mainly at high elevations in the subalpine zone near the upper tree line. It can more often be found at the outer fringes of a forest than in the forest itself. == Ecology ==

Pinus flexilis is an important source of food for several species, including red squirrels and Clark's nutcrackers, the latter being an important distributor of seeds. In a relic, low elevation population, seeds are also dispersed by small rodents. American black bears and grizzly bears may raid squirrel caches for limber pine nuts. The species is generally shade tolerant and resistant to fire, but does not thrive in dense habitats, instead occurring in areas relatively hostile to other species. Threats Limber pine is susceptible to white pine blister rust, caused by 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 little hope 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 tree has also been damaged by bark beetle epidemics, particularly at drought-affected low elevations. == Cultivation ==

The popular cultivar P. flexilis 'Vanderwolf's Pyramid' is widely available as an ornamental tree for gardens. 'Vanderwolf's Pyramid' derives from P. reflexa, though it is usually listed in nursery catalogs under P. flexilis. The Southwestern white pine is popular as a windbreak tree or an ornamental tree due to its drought tolerance. It is also grown as a Christmas tree, liked for the soft needles but with stiffer branches than an Eastern white pine. ==Uses==

The large seeds are edible, and were reportedly consumed by Native Americans in Montana. == See also ==