Physiognomy and Structure: Mesic conifer forests, ranging from closed-canopy to more open "savanna-like" woodlands, over deciduous shrub layer, or forb-rich herbaceous layer.

Floristics: Abies grandis is dominant in these forests and Pseudotsuga menziesii commonly shares the canopy. Pinus monticola, Picea engelmannii, Pinus contorta, Abies lasiocarpa, and Larix occidentalis are major associates. On most mesic sites, intermediate to older age stands of this forest group may support some Thuja plicata and Tsuga heterophylla in the overstory. Common shrubs include Paxistima myrsinites, Amelanchier alnifolia, Rosa gymnocarpa, Acer glabrum, Spiraea betulifolia, Symphoricarpos albus, Cornus canadensis, Rubus parviflorus, Menziesia ferruginea, Taxus brevifolia, and Vaccinium membranaceum. Composition of the herbaceous layer reflects local climate and degree of canopy closure; it is typically highly diverse in all but closed-canopy conditions. Clintonia uniflora, Linnaea borealis, Aralia nudicaulis, and Xerophyllum tenax are common forbs in these forests. Other forbs include Actaea rubra, Adenocaulon bicolor, Arnica latifolia, Galium triflorum, Goodyera oblongifolia, Orthilia secunda, Streptopus amplexifolius, Prosartes hookeri (= Disporum hookeri), Thalictrum occidentale, and Trillium ovatum. Asarum caudatum occurs in the Kootenai and Yak river areas of extreme northwestern Montana, north-central Idaho and in the Blue Mountains in Oregon. Graminoids usually form a very minor component and typically include Bromus vulgaris and minor amounts of Carex geyeri, Elymus glaucus, Festuca subulata, and Oryzopsis asperifolia. This group also includes woodlands or "savannas" of the deciduous conifer Larix occidentalis. Important low-growing shrubs include Arctostaphylos uva-ursi, Spiraea betulifolia, and Vaccinium cespitosum; taller shrubs can include Acer glabrum, Ceanothus velutinus, Shepherdia canadensis, Physocarpus malvaceus, Rubus parviflorus, or Vaccinium membranaceum. Herbaceous species include Calamagrostis rubescens, Clintonia uniflora, Linnaea borealis, or Xerophyllum tenax.

Dynamics:  Typically, stand-replacement fires have 150- to 500-year return intervals, with moderate-severity fire intervals of 50-100 years. Abies grandis forests include many sites dominated by Pseudotsuga menziesii and Pinus ponderosa which were formerly maintained by wildfire, and may now be dominated by Abies grandis (a fire-sensitive, shade-tolerant species) due to fire exclusion (Lillybridge et al. 1995, Chappell et al. 1997). Pre-European settlement fire regimes were typically of frequent, low-intensity surface fires, maintaining relatively open stands of a mix of fire-resistant species. With the advent of effective fire suppression, longer fire-return intervals are now the rule, and mixed-stature stands with Abies grandis in various size classes now create ladder fuels making these forests more susceptible to high-intensity, stand-replacing fires (Cooper et al. 1987, Lillybridge et al. 1995).

Larix occidentalis is a long-lived species (in excess of 700 years in the northern Rocky Mountains), and thus stands of western larch are themselves persistent. However, the life of Larix-dominated stands probably rarely exceeds 250 years due to various mortality sources and the in-growth of shade-tolerant species, especially on mesic sites. Occurrences of Larix occidentalis stands are generated by stand-replacing fire, the fire-return interval for which is speculated to be approximately 80 to 200 years (Cooper et al. 1987). These sites may be maintained in a seral status for hundreds of years since Larix occidentalis is a long-lived species and the understory is often dominated by Pseudotsuga, which will grow into the upper canopy. The potential dominants, typically Abies lasiocarpa, Picea engelmannii, and/or Abies grandis or rarely Tsuga heterophylla or Thuja plicata, establish and grow on these sites, presenting the distinct probability, given the fire-return intervals for this type, that the "climax" (long-term stable) condition is never attained. It has been noted in northern Idaho that, following disturbance (particularly logging) in some mesic-site occurrences, Larix occidentalis does not necessarily replace itself, the first tree-dominated successional stages being dominated by Pseudotsuga menziesii, Pinus contorta, or less frequently by more shade-tolerant species (Cooper et al. 1987); this response is a consequence of the episodic nature of favorable cone crop years in Larix occidentalis.