Physiognomy and Structure: Generally, these are productive forests, ranging from closed-canopy to more open "savanna-like" woodlands. Composed of [usually] tall, long-lived, needle-leaved evergreen trees, sometimes composed of just one tree species, but more often are of mixed composition. Deciduous hardwoods intermingle in some occurrences; deciduous conifers are dominant in some areas. Deciduous tall and short shrubs, and perennial graminoids, forbs or ferns often form shrub and herbaceous layers, respectively. Often there is high cover of mosses. Some occurrences may lack the shrub layer. Some of these forests are the most diverse of any Rocky Mountain forest, sometimes approaching or equaling the within-stand diversity of some eastern North American forests, but the diversity resides in the shrub and herb taxa, not the trees.

Floristics: In the grand fir - Douglas-fir zone, Abies grandis is dominant and Pseudotsuga menziesii commonly shares the canopy. Abies lasiocarpa, Larix occidentalis, Picea engelmannii, Pinus contorta, and Pinus monticola are major associates. On most mesic sites, intermediate to older age stands may support some Thuja plicata and Tsuga heterophylla in the overstory. In other locations, Tsuga heterophylla and Thuja plicata are the dominants, while Pseudotsuga menziesii and Abies grandis commonly share the canopy, and Pinus monticola, Pinus contorta, Abies lasiocarpa, and Larix occidentalis are major associates. Picea engelmannii and Abies lasiocarpa may be present but only on the coldest sites, and Pinus ponderosa may be present but only on the warmest and driest sites or mid-seral, post-fire sites. In central British Columbia, Tsuga heterophylla and/or Thuja plicata are the dominants and are generally associated with some Picea glauca x engelmannii, Abies lasiocarpa, or Pseudotsuga menziesii. Deciduous hardwood species occur, but typically are not dominant; they include Populus tremuloides and Betula papyrifera.

Common shrubs include Acer glabrum, Amelanchier alnifolia, Cornus nuttallii, Mahonia nervosa, Menziesia ferruginea, Paxistima myrsinites, Rosa gymnocarpa, Rubus parviflorus, Spiraea betulifolia, Symphoricarpos albus, Symphoricarpos hesperius, Taxus brevifolia, and Vaccinium membranaceum. Oplopanax horridus is common in the understory in depressional areas with high water tables. Composition of the herbaceous layer reflects local climate and degree of canopy closure; it is typically highly diverse in all but closed-canopy conditions. Aralia nudicaulis, Clintonia uniflora, Linnaea borealis, Tiarella trifoliata, Viola orbiculata, Cornus canadensis, and Xerophyllum tenax are common forbs in these forests. Other forbs include Actaea rubra, Adenocaulon bicolor, Anemone piperi, Arnica latifolia, Coptis occidentalis, Galium triflorum, Goodyera oblongifolia, Orthilia secunda, Prosartes hookeri (= Disporum hookeri), Streptopus amplexifolius, Thalictrum occidentale, and Trillium ovatum. In the eastern Cascades, Acer circinatum, Achlys triphylla, Anemone deltoidea, Chrysolepis chrysophylla, and Vancouveria hexandra are more common. Graminoids usually form a very minor component and typically include Bromus vulgaris and minor amounts of Carex deweyana, Carex geyeri, Elymus glaucus, Festuca subulata, and Oryzopsis asperifolia. Ferns and fern allies also form an important component of the understory in many occurrences and commonly include Athyrium filix-femina, Botrychium spp., Dryopteris filix-mas, Dryopteris expansa (= Dryopteris assimilis), Equisetum spp., and Gymnocarpium dryopteris. Under closed-canopy conditions, a dense moss layer can form on the forest floor.

This macrogroup 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, Physocarpus malvaceus, Rubus parviflorus, Shepherdia canadensis, or Vaccinium membranaceum. Herbaceous species include Calamagrostis rubescens, Clintonia uniflora, Linnaea borealis, or Xerophyllum tenax.

Dynamics:  These mesic and productive forests tend to have long fire return-intervals, ranging from 150 to over 500 years for stand-replacing fires, and with moderate-severity fire intervals of 50-100 years. Gap dynamics are important in older stands. Larix occidentalis woodlands are maintained post-establishment by frequent, low-severity surface fires.

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 of grand fir - Douglas-fir forests 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), but are maintained by a higher frequency, surface-fire regime. Fire suppression has led to invasion of the more shade-tolerant tree species Abies grandis, Abies lasiocarpa, Picea engelmannii, or Tsuga spp. and loss of much of the single-story canopy woodlands. Larix occidentalis communities occur in settings where low-intensity, high-frequency fires create open larch woodlands. 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.

The western red-cedar - western hemlock forests are very productive forests which have been priority stands for timber production. Typically, stand-replacement fire-return intervals are 150-500 years in the Cascades, or 150-500 years in the Northern Rockies, with moderate-severity fire-return intervals of 50-100 years. Thuja and Tsuga are capable of remaining dominant within these forests due to their longevity and Thuja''s ability to regenerate vegetatively. In the absence of disturbance, both species continue to regenerate under shaded conditions. Under closed-canopy conditions, both species favor vegetative reproduction over sexual reproduction, thus intermediate and young trees are found under these conditions.