Physiognomy and Structure: No Data Available

Floristics: This association is characterized by an open canopy (15-40% cover). Pinus albicaulis with scattered Picea engelmannii and Abies lasiocarpa form the overstory with the subcanopy dominated by Abies lasiocarpa. Trees may be scattered or clustered in groves and are often wind-deformed and stunted, growing only 6-18 m (20-60 feet) tall or less. Occasionally Pinus flexilis or Pseudotsuga menziesii may be present, but sites are generally too cold (Pfister et al. 1977). The undergrowth is variable, depending on relative moisture, and typically depauperate. Shrub cover is highly variable in amount and species composition. Juniperus communis can dominate the dwarf-shrub layer (<0.5 m tall, though a short shrub in more optimal habitats) with 5-15% cover; Arctostaphylos uva-ursi is often present with low cover. Other shrubs may be present; Ribes montigenum, Ribes lacustre, Vaccinium membranaceum, and Vaccinium scoparium occur scattered. The herbaceous layer is typically sparse (<15% cover). Herbaceous species of moderate to high constancy include Antennaria spp., Arnica latifolia, Carex geyeri, Carex rossii, Chamerion angustifolium, Ligusticum filicinum, Lupinus argenteus, Packera neomexicana (= Senecio neomexicanus), Penstemon virens, Sedum lanceolatum, Senecio crassulus, Selaginella densa, Solidago multiradiata, Thalictrum fendleri, and Thermopsis divaricarpa. Disturbed sites, especially those impacted by sheep grazing, often have a high cover of Polygonum phytolaccifolium.

Dynamics:  Pinus albicaulis is a slow-growing, long-lived conifer that is common at higher elevations in the upper subalpine zone. It typically occurs in a mosaic of tree islands and meadows where it often colonizes sites and creates habitat for less hardy tree species. In lower subalpine forests, it is a seral species, establishing after a large disturbance such as stand-replacing fire or avalanche, or it is restricted to dry, rocky ridges where it competes well with shade-tolerant tree species. Without disturbance it will be overtopped in 100-120 years by faster growing, shade-tolerant species such as Abies lasiocarpa, Picea engelmannii, Pseudotsuga menziesii, and Tsuga mertensiana. Although crown fires and hot surface fires kill Pinus albicaulis, it tolerates low-intensity surface fires that will kill the shade-tolerant understory. Fire intervals range from 30-300 years.

Birds and small mammals often eat and cache the large, wingless pine seeds and are responsible for the dispersal of this species. Most important is the Clark''s nutcracker, which can transport the seeds long distances and cache them on exposed windswept and burned-over sites. This results in the regeneration of pines in clumps from forgotten caches (Eyre 1980, Steel et al. 1983, Burns and Honkala 1990a, Schmidt and McDonald 1990).

Pests include the mountain pine beetle (Dendroctonus ponderosae), which has killed many mature trees in the past, during epidemics where populations of the beetles build up in lower elevation Pinus contorta stands then move up into the Pinus albicaulis (Steel et al. 1983, Burns and Honkala 1990a, Schmidt and McDonald 1990). The exotic pathogen white pine blister rust (Cronartium ribicola) is attacking and killing Pinus albicaulis trees in many parts of the interior northwestern U.S. It is especially destructive in more mesic habitats that favor infection of its alternate host Ribes spp. Pinus albicaulis is very susceptible to this disease; incidence of resistant trees is on the order of 1 in 10,000 trees. The best hope of salvaging this species as a viable and influential ecosystem component is propagating individuals that have high genetic resistance to blister rust (Steel et al. 1983, Burns and Honkala 1990a, Schmidt and McDonald 1990).