This ecological system is composed of highly variable montane coniferous forests found in the interior Pacific Northwest, from southernmost interior British Columbia, eastern Washington, eastern Oregon, northern Idaho, western and north-central Montana, and south along the east slope of the Cascades in Washington and Oregon. In central Montana it occurs on mountain islands (the Snowy Mountains). This system is associated with a submesic climate regime with annual precipitation ranging from 50 to 100 cm, with a maximum in winter or late spring. Winter snowpacks typically melt off in early spring at lower elevations. Elevations range from 460 to 1920 m. Most occurrences of this system are dominated by a mix of Pseudotsuga menziesii and Pinus ponderosa (but there can be one without the other) and other typically seral species, including Pinus contorta, Pinus monticola (not in central Montana), and Larix occidentalis (not in central Montana). Picea engelmannii (or Picea glauca or their hybrid) becomes increasingly common towards the eastern edge of the range. The nature of this forest system is a matrix of large patches dominated or codominated by one or combinations of the above species; Abies grandis (a fire-sensitive, shade-tolerant species not occurring in central Montana) has increased on many 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 ground fires that maintained relatively open stands of a mix of 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. They are very productive forests which have been priorities for timber production. They rarely form either upper or lower timberline forests. Understories are dominated by graminoids, such as Pseudoroegneria spicata, Calamagrostis rubescens, Carex geyeri, and Carex rossii, that may be associated with a variety of shrubs, such as Acer glabrum, Juniperus communis, Physocarpus malvaceus, Symphoricarpos albus, Spiraea betulifolia, or Vaccinium membranaceum on mesic sites. Abies concolor and Abies grandis X concolor hybrids in central Idaho (the Salmon Mountains) are included here but have very restricted range in this area. Abies concolor and Abies grandis in the Blue Mountains of Oregon are probably hybrids of the two and mostly Abies grandis.
Information Source: http://www.natureserve.org/explorer/