Physiognomy and Structure: Vegetation included in this alliance has an open tree canopy that is typically to 3-10 m tall. The canopy is dominated by evergreen needle-leaved trees. A sparse to moderately dense short-shrub and/or dwarf-shrub layer is present. If present, both shrub layers may be dominated by broad-leaved or microphyllous deciduous shrubs. A sparse to moderately dense herbaceous layer dominated by perennial graminoids is often present. Perennial forbs have low cover. Annual forbs and grasses may be seasonally present.

Floristics: Stands have an open canopy dominated by Pinus flexilis typically 3-10 m tall and may be codominated by Juniperus scopulorum or, less commonly, Juniperus osteosperma. The understory typically has an open to moderately dense shrub layer (10-40% cover). Shrubs such as Amelanchier utahensis, Artemisia tridentata, Cercocarpus montanus, Purshia tridentata, and Rhus trilobata are common. Total shrub cover is typically >10%, but if less, then shrub cover exceeds herbaceous layer cover. The herbaceous layer is sparse to moderately dense and is composed primarily of graminoids such as Achnatherum hymenoides (= Oryzopsis hymenoides), Bouteloua gracilis, Festuca campestris, Leucopoa kingii (= Festuca kingii), Koeleria macrantha, and Pseudoroegneria spicata. Scattered forbs may include species of Achillea, Antennaria, Arenaria, Arnica, Astragalus, Erigeron, Eriogonum, Hymenopappus, Hymenoxys, Liatris, Sedum, Solidago, and Thermopsis. In six plots in the Little Missouri National Grassland in western North Dakota, the average cover for each of the strata was trees 38%, shrubs 21%, graminoids 20%, and forbs 9% (USFS 1992).

Dynamics:  Although some of the conifers that are typically codominant in Pinus flexilis stands are late-successional species, they are not likely to displace Pinus flexilis. This is because most of these stands occur on harsh sites where Pinus flexilis is more competitive than most other conifer species. These stands are generally considered to be topographic or edaphic "climax" stands (Cooper 1975, Eyre 1980). Even in stands at lower elevations, such as prairie breaks, it is unlikely that other coniferous species will become dominant (Eyre 1980). Because Pinus flexilis occurs over a broad range of elevations, it can also be important as a post-fire seral species on drier sites in the Rocky Mountains (Cooper 1975, Peet 1988). Peet (1978a) reported apparent competitive displacement with Pinus flexilis in Colorado. He noted that Pinus flexilis may dominate xeric sites from low to high elevations, except where Pinus aristata or Pinus albicaulis occur. There, Pinus flexilis is largely restricted to lower elevation, rocky sites. Peet (1978a) also reported that Pinus flexilis occurs in the less xeric Pinus contorta and Pinus ponderosa habitats.

Birds and small mammals often eat and cache the large, wingless pine seeds. Most important is the Clark''s nutcracker, which can transport the seeds long distances and cache them on exposed windswept sites (Lanner and Vander Wall 1980). This results in the regeneration of pines in clumps from forgotten caches (Eyre 1980, Steele et al. 1983).