There are four stages in the life cycle of the whitebark pine: seed, seedling, sapling and mature trees, also referred to as reproductive adults. Seeds are produced in female cones and once on the ground may take two years or more, up to 11 years in some cases, to germinate. Germinated seeds become seedlings that are between 3 to 4 inches tall (8 and 10 centimeters) with a taproot that can measure between 5 to 7 inches (13 to18 centimeters), with 7 to 9 cotyledons, also known as the embryonic first leaves, as documented by S.F. Arno and R.J. Hoff in 1990. Whitebark pine seedlings may persist for multiple years, depending on growing conditions, until reaching the sapling stage of the life cycle. Whitebark pine saplings persist for few to many years, depending on growing conditions, until they produce male and female cones. Mature reproductive whitebark pines contain both female and male cones, which is known as monoecious reproduction, and can survive on the landscape for hundreds of years.

Whitebark pinemay occur as a climax species, or an early to seral mid-successional stage codominant associated with other tree species. Although it occasionally occurs in pure or nearly pure stands at high elevations, it more typically occurs in stands of mixed species in a variety of forest community types. Whitebark pineis typically 16 to 66 feet tall (5 to 20 meters) with a rounded or irregularly spreading crown shape. On higher density conifer sites, whitebark pinetends to grow as tall, single-stemmed trees. On open, more exposed sites, it tends to have multiple stems as documented by W.W. McCaughey and D.F. Tomback in 2001. Above tree line, it grows in a krummholz form, meaning stunted, shrub-like growth, as documented by S.F. Arno and R.J. Hoff in 1989. Production of male and female cones in mature trees will begin sometime from June to September depending on environment as documented by W.W. McCaughey and D.F. Tomback in 2001 and later by A. Sala and others in 2012. Female cones take 2 years to fully develop as documented by Weaver in 2001. Its characteristic dark brown to purple seed cones are 2 to 3 inches long (5 to 8 centimeters) and grow in clusters of 2 to 4 cones at the outer ends of upper branches as documented by R.C. Hosie in 1969.

Like the other life stages, the mature tree life stage of whitebark pine is moderately shade-tolerant and therefore high-quality habitat is often characterized by a more open canopy as documented by P.E. Maloney in 2014, or lower competition with other overstory trees. Whitebark pineis a slow-growing, long-lived tree with a life span between 500 years and 1,000 years as documented by S.F. Arno and R.J. Hoff in 1989 and later by D.L. Perkins and T.W. Swetnam in 1996. This is provided it is located in an area with lower competition, such as a more open canopy with low litter depth and high rock cover, as noted by P.E. Maloney in 2014. Therefore, in addition to the four general needs for all life stages, mature whitebark pine trees require a more open canopy, dispersal of seeds by Clark’s nutcracker, two summers of suitable temperatures and precipitation for pollinated cones to mature, as well as levels of nitrogen and phosphorus that are adequate to restore values after being depleted in masting year.

Mature reproductive whitebark pines contain both female and male cones, known as monoecious reproduction. Production of male and female cones in mature trees will begin sometime from June to September depending on environment as documented by W.W. McCaughey and D.F. Tomback in 2001 and later by A. Sala and others in 2012. Female cones take 2 years to fully develop as documented by Weaver in 2001. Seeds are produced in female cones and once on the ground may take two years or more, and in some cases up to 11 years to germinate. While whitebark pineis almost exclusively dependent upon Clark’s nutcracker for seed dispersal, the reverse is not true as Clark’s nutcracker will forage on seeds from numerous species of trees. The frequency of nutcracker occurrence and probability of seed dispersal from a whitebark pineforest is strongly associated with the number of available cones. The number of cones produced is dependent on stand condition and tree abundance as documented by L.E. Barringer and others in 2012. A threshold of 1,000 cones per 2.47 acres (1 hectare) may be needed for a high likelihood of seed dispersal by nutcrackers. Additionally, this level of cone production occurs in forests with a live basal area, where the total stem cross-sectional area of square meters per area (hectare) is greater than 5 square meters per hectare as documented by W.T. McKinney and others in2009. For an adult Clark’s nutcracker to survive a subalpine winter, accounting for those seeds consumed by rodents and those fed to juvenile nutcrackers, it would need to cache seeds from between 767 to 2,130 cones as noted by W.T. McKinney and others in 2009. Clark’s nutcrackers are able to assess cone crops, and if there are insufficient seeds to cache, they will emigrate in order to survive as noted by W.T. McKinney and others in 2009. Other seed predators such as Steller’s jays, deer mice and chipmunks provide limited dispersal of whitebark pine seeds as documented by W.W. McCaughey and D.F. Tomback in 2001.

Whitebark pinemay occur as a climax species, or an early to seral mid-successional stage codominant associated with other tree species. Although it occasionally occurs in pure or nearly pure stands at high elevations, it more typically occurs in stands of mixed species in a variety of forest community types. Whitebark pineis typically 16 to 66 feet tall (5 to 20 meters) with a rounded or irregularly spreading crown shape. On higher density conifer sites, whitebark pinetends to grow as tall, single-stemmed trees. On open, more exposed sites, it tends to have multiple stems as documented by W.W. McCaughey and D.F. Tomback in 2001. Above tree line, it grows in a krummholz form, meaning stunted, shrub-like growth, as documented by S.F. Arno and R. J. Hoff in 1989.

Limber pine is difficult to distinguish from whitebark pine from the air, which makes aerial estimates of tree losses difficult to identify to species.

In general, the upper elevational limits of whitebark pinedecrease with increasing latitude throughout its range as documented by W.W. McCaughey and W.C. Schmidt in 2001. The elevational limit of the species ranges from approximately 2,950 feet (900 meters) at its northern limit in British Columbia, up to 12,000 feet (3,660 meters) in the Sierra Nevada as noted by W.W. McCaughey and W.C. Schmidt in 2001. Whitebark pineis typically found growing at subalpine treeline, or with other high-mountain conifers just below the treeline, and subalpine zone as noted by S.F. Arno and R.J. Hoff in 1990 and later by W.W. McCaughey and W.C. Schmidt in 2001. In the Rocky Mountains, common associated tree species include P. contorta var. latifolia (lodgepole pine), Picea engelmannii (Engelmann spruce), Abies lasiocarpa (subalpine fir) and Tsuga mertensiana (mountain hemlock). Common associated tree species are similar in the Sierra Nevada and Blue and Cascade Mountains,except lodgepole pine is present as P. contorta var. murrayana (Sierra-Cascade lodgepole pine), mountain hemlock is absent from the Blue Mountains as documented by S.F. Arno and R.J. Hoff in 1990 and later by W.W. McCaughey and W.C. Schmidt in 2001. Engelmann spruce and subalpine fir are absent in the Sierra Nevada.