Physiognomy and Structure: This group is characterized by Pinus albicaulis or Larix lyallii, sometimes associated with other conifers, which form woodlands and occasionally forests. Trees are often stunted and flagged as a result of harsh cold and wind. The understory is variable depending on substrates ranging from sparse on rockier sites to dense on more mesic sites and typically characterized by heaths and graminoids.

Floristics: These woodlands are mostly dominated by Pinus albicaulis or Larix lyallii and occasionally codominated by Abies lasiocarpa. Understories range from sparse to dense and are occupied by heath species, including Arctostaphylos uva-ursi, Vaccinium membranaceum, Vaccinium myrtillus, Menziesia ferruginea, and Vaccinium scoparium. The herbaceous layer is sparse under dense shrub canopies or may be dense where the shrub canopy is open or absent. Common species include Ligusticum grayi, Xerophyllum tenax, Festuca idahoensis, Carex rossii, Calamagrostis rubescens, and Luzula glabrata var. hitchcockii.

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 crownfires and high-intensity 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 beetle 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, and the only real hope is propagating individuals that have high genetic resistance to blister rust (Steel et al. 1983, Burns and Honkala 1990a, Schmidt and McDonald 1990, Tomback et al. 2001).

Larix lyallii is a very slow-growing, long-lived tree, with individuals attaining up to 1000 years in age (Richards 1981). It is generally intolerant of shade from other trees, but extreme environmental conditions limit competition. Reproduction is typically by seed and is most favorable on moist mineral soil. Seedling growth is initially very slow and accelerates after an extensive root system is established. Major disturbances to stands of this group are windthrow and snow avalanches. Lightning damage to individual trees is common, but sparse canopies and rocky terrain serve to limit the spread of fire.