About Pinus flexilis var. reflexa Engelm.
Pinus flexilis var. reflexa Engelm. gets its common name "limber" and the specific epithet flexilis from its pliant branches. Its needles are around 8 centimeters (3 1/4 inches) long and colored a dark, blueish green. Its bark is dark grey and heavily creased, and its pale wood is lightweight and soft. Limber pine is typically a high-elevation pine that often marks the tree line, growing either alone or alongside whitebark pine (Pinus albicaulis), either of the bristlecone pines, or lodgepole pine (Pinus contorta). In favorable growing conditions, it grows into a tree reaching 20 metres (65 feet) tall, and rarely reaches 25 m (80 ft). On exposed tree line sites, mature trees are much smaller, only reaching heights of 5–10 m (15–35 ft). On steeply-sloping, rocky, windswept terrain in the Rocky Mountains of southern Alberta, limber pine is even more stunted; it grows in old stands where mature trees consistently stay shorter than 3 m (10 ft). One of the world's oldest living limber pines grows on the banks of the upper North Saskatchewan River at Whirlpool Point in Alberta. Recent measurements recorded a maximum girth of 185 inches. In 1986, two researchers retrieved a 10 cm core sample and counted 400 rings; extrapolating this data gives an estimated age close to 3,000 years. The largest portion of limber pine's range lies in the Rocky Mountains, extending from southwest Alberta and southeastern British Columbia south through Colorado and New Mexico into the northern states of Mexico. It also grows across the Great Basin states of Nevada and Utah, in the eastern Sierra Nevada and White Mountains of Northern California, and in the San Bernardino and San Gabriel Mountains of the Transverse Ranges in Southern California. Continuing south, the species occurs in the San Jacinto Mountains, Santa Rosa Mountains, and Hot Springs Mountain of the Peninsular Ranges. Small disjunct populations exist in eastern Oregon, western North Dakota, western Nebraska, and the Black Hills of South Dakota. It grows across a wide range of altitudes that varies with latitude, from 850 to 3,810 m (2,790 to 12,500 ft). In the northern half of its range, it grows in the montane zone near the lower tree line; between the 45th and 40th parallels in the middle of its range, 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 is more often found on the outer fringes of a forest than within dense forest. Pinus flexilis is an important food source for several species, including red squirrels and Clark's nutcrackers; Clark's nutcrackers are also important distributors of limber pine seeds, and evidence suggests limber pines co-evolved with this bird, which acts as the primary seed disperser. In a relic low elevation population, seeds are also dispersed by small rodents. American black bears and grizzly bears may raid squirrel caches to eat limber pine nuts. Squirrels, Northern flickers, and mountain bluebirds often nest in limber pine trees. Evidence suggests P. flexilis has a symbiotic relationship with nitrogen-fixing bacteria that live in its needles. The species is generally shade tolerant and fire resistant, but does not thrive in dense habitats, instead growing in areas that are relatively hostile to other species. The popular cultivar P. flexilis 'Vanderwolf's Pyramid' is widely sold as an ornamental tree for gardens. 'Vanderwolf's Pyramid' originates from P. reflexa, though it is usually listed in nursery catalogs under P. flexilis. Southwestern white pine is popular as a windbreak or ornamental tree due to its drought tolerance. It is also grown as a Christmas tree, valued for its soft needles and stiffer branches than Eastern white pine. The large seeds of Pinus flexilis are edible, and Native Americans in Montana reportedly consumed them.
