Pinus contorta, with the common names lodgepole pine, shore pine, twisted pine, and contorta pine, is an evergreen species of conifer tree. It is a common pine in western North America, found near the ocean shore and in dry montane forests to the subalpine, but is rare in lowland rain forests.
Description Depending on subspecies, Pinus contorta grows as an evergreen shrub or tree. The shrub form is krummholz and is approximately 1 to 3 meters (3 to 10 ft) high. The thin and narrow-crowned tree can grow 40 to 50 m (130 to 160 ft) high and achieve up to 2 m (7 ft) in diameter at chest height. The murrayana subspecies is the tallest. The crown is rounded and the top of the tree is flattened. In dense forests, the tree has a slim, conical crown. The formation of twin trees is common in some populations in British Columbia. The elastic branches stand upright or overhang and are difficult to break. The branches are covered with short shoots that are easy to remove. The species name is contorta because of the twisted, bent pines (shore pine) found at coastal areas and the tree's twisted needles. Pinus contorta is occasionally known under several English names: black pine, scrub pine, and coast pine. P. contorta subsp. latifolia will hybridise with the closely related jack pine (P. banksiana). The bark of lodgepole pine is thin, scaly and grayish brown. Shore pine bark is somewhat thick and corky, fissuring into a checkered pattern. Some lodgepole pines have been reported in low elevations with features closer to those of the shore pine, including the bark. Tamarack pine can grow up to centuries old and lodgepole pines in Yellowstone Park have survived over 300 years.
Foliage
The egg-shaped growth buds are reddish-brown and between 20 and 30 millimeters (3⁄4 and 1+1⁄4 in) long. They are short pointed, slightly rotated, and very resinous. Spring growth starts in beginning of April and the annual growth is completed by early July. The dark and mostly shiny needles are pointed and 4 to 8 centimeters (1+1⁄2 to 3 in) long and 0.9 to 2 mm (1⁄32 to 3⁄32 in) wide. The needle edge is weakly to strongly serrated. The needles are in pairs on short shoots and rotated about the shoots' longitudinal axes. In Alberta above 2,000 m (6,600 ft), 1 to 5 needles occur per short shoot. A population with a high proportion of three-needled short shoots occurs in the Yukon. Needles live an average of four to six years, with a maximum of 13 years. The foliage of lodgepole pine is yellow-green as compared to shore pine, which is dark green.
Cones The cones of lodgepole and shore pine begin to be produced when the trees are about ten years old. The cones are 3–7 cm (1–3 in) long, with prickles on the scales. Many populations of the Rocky Mountain subspecies, P. contorta subsp. latifolia, have serotinous cones. This means that the cones are closed and must be exposed to high temperatures, such as from forest fires, in order to open and release their seeds. The variation in their serotiny has been correlated with wildfires and mountain pine beetle attacks. The cones of the coastal Pacific subspecies, P. contorta subsp. contorta, are typically non-serotinous, and those of the inland Pacific subspecies, P. contorta subsp. murrayana, are completely non-serotinous. Sometimes cones will become buried by the continued growth of a branch. If the seeds are collected, they have germinated as much as 150 years after confinement.
Distribution Pinus contorta occurs from upper, dry montane forests to the subalpine region of western North America. It can be found on the western side of the Cascades, in inland British Columbia, and on the Rocky Mountains in Alberta, except where it is too high and dry. Lodgepole pine can tolerate relatively hostile environments such as high-elevation volcanic rock in Central Oregon (e.g. Crater Lake) and thin soils on the eastern slope of the Cascades. Further south, the species can be found in higher elevations up to 3,350 m (10,990 ft) above sea level, particularly in southern Colorado. It is rare in lowland rain forests. Shore pine can be found in very infertile soils in coastal regions from Southeast Alaska to Northern California. Lodgepole and shore pine can be found intermingled (and apparently hybridized) north of Puget Sound. Less dependent on fire, tamarack pine can be found in California's upper mountains and mingled with lodgepole in Oregon. Pinus contorta can be found in the closed-cone pine forest of coastal California.
Ecology Pinus contorta is a fire-adapted species, often regenerating densely following wildfire. The species displays characteristically poor self pruning and thin bark, features which often lead to a high rate of mortality following fire. Importantly however, the heat from fire results in the opening of serotinous cones and the release of seeds. This in turn allows the species to regenerate well following catastrophic fire, and maintain its place in forest landscapes as an early successional species. Some populations do sustain themselves in the absence of regular fire, where wind through, ice storms, and land slides also act as stand replacing disturbances.
The natural fire regime for this species is primarily driven by climate. The fires occur most often after years of drought . Forests in the upper montane to subalpine region experience much moisture in the winter via snow. The density of tree stands with the species inhibit the establishment of an understory (allowing ladder fuel to form), and surface fire is rare regardless. Thus, infrequent but severe fires dominate this species. An example of the climate that plays a huge role in the fire regime of the species is quite complex. There are three different oscillations that play a major role in droughts. These are the Pacific decadal oscillation (PDO), Atlantic multidecadal oscillation (AMO) and El Niño (ENSO). A combination of these oscillations being in effect (+) or not in effect (−) have a global effect on the water available to these forests. The combination of AMO +, ENSO − and PDO − means there is going to be a drought and likely a severe subalpine fire.
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