Physiognomy and Structure: Vegetation included in this alliance is characterized by open to closed stands of evergreen needle-leaved trees 15-50 m tall. There is a sparse cover of subcanopy trees (5-15 m tall). The understory is variable. Shrubs (0.5-2 m tall) are usually present and may be dense enough (>10% cover) to form a layer. However, the herbaceous layer usually characterizes the understory and is dominated by graminoids such as perennial bunch grasses and upland dry sedges.

Floristics: This forest alliance has a moderately dense to closed canopy dominated by a mix of Pseudotsuga menziesii and Pinus contorta (but there can be stands without the latter) and sometimes with other species, including Pinus ponderosa, Pinus monticola, and Larix occidentalis. The nature of this forest system is a matrix of large patches dominated or codominated by one or combinations of the above species. In some stands, Abies grandis (a fire-sensitive, shade-tolerant species not occurring in central Montana) has increased on sites once dominated by Pseudotsuga menziesii and Pinus ponderosa, which were formerly maintained by low-severity wildfire. Presettlement fire regimes may have been characterized by frequent, low-intensity surface fires that maintained relatively open stands of a mix of these fire-resistant species. Under present conditions, the fire regime is mixed-severity and more variable, with stand-replacing fires more common, and the forests are more homogeneous. With vigorous fire suppression, longer fire-return intervals are now the rule, and multi-layered stands of Pseudotsuga menziesii, Pinus ponderosa, and/or Abies grandis provide fuel "ladders," making these forests more susceptible to high-intensity, stand-replacing fires. The understory is dominated by graminoids, such as Calamagrostis rubescens, Carex geyeri, Carex rossii, and Pseudoroegneria spicata. On mesic sites, a variety of shrubs such as Acer glabrum, Juniperus communis, Physocarpus malvaceus, Symphoricarpos albus, Spiraea betulifolia, or Vaccinium membranaceum may occur.

Dynamics:  The nature of this forest system is a matrix of large patches dominated or codominated by one or combinations of the above species. In some stands, Abies grandis (a fire-sensitive, shade-tolerant species not occurring in central Montana) has increased on sites once dominated by Pseudotsuga menziesii and Pinus ponderosa, which were formerly maintained by low-severity wildfire. Presettlement fire regimes may have been characterized by frequent, low-intensity surface fires that maintained relatively open stands of a mix of these fire-resistant species. Under present conditions, the fire regime is mixed-severity and more variable, with stand-replacing fires more common, and the forests are more homogeneous. With vigorous fire suppression, longer fire-return intervals are now the rule, and multi-layered stands of Pseudotsuga menziesii, Pinus ponderosa, and/or Abies grandis provide fuel "ladders," making these forests more susceptible to high-intensity, stand-replacing fires.