Physiognomy and Structure: Forests within this alliance are characterized by evergreen needle-leaved trees 20-50+ m in height.

Floristics: Upper tree canopy is a mixed codominance of Abies lowiana (= Abies concolor var. lowiana) and Pseudotsuga menziesii. Other tree species often present include Calocedrus decurrens, Chrysolepis chrysophylla, Cornus nuttallii, Pinus lambertiana, Pinus ponderosa, Quercus chrysolepis, and Quercus kelloggii. Pinus lambertiana has less than 5% absolute cover, and less than 2% relative cover. Stands can have well-developed shrub layers or no shrub layer, and stands can have greater diversity of mixed trees in the upper canopy. Understory species are characteristic of the Vancouverian flora which differentiates this alliance from its Rocky Mountain counterpart. Characteristic understory and undergrowth species include Anemone deltoidea, Ceanothus cordulatus, Chrysolepis chrysophylla, Corylus cornuta, Holodiscus discolor, Notholithocarpus densiflorus (= Lithocarpus densiflorus), Mahonia aquifolium, Quercus sadleriana, Quercus vacciniifolia, Rubus nivalis, Taxus brevifolia, Toxicodendron diversilobum, and Whipplea modesta.

These are mixed conifer forests in which Abies lowiana is always present either in the canopy or in the tree-regeneration layer. Other conifers, such as Calocedrus decurrens, Pinus lambertiana, Pinus ponderosa, Pseudotsuga menziesii, are usually present in the canopy or understory. Notholithocarpus densiflorus may occur in small stands or as scattered individuals throughout these forests. A distinctive group of cold-deciduous or sclerophyllous broad-leaved trees are sometimes common in these stands, including Arbutus menziesii, Quercus kelloggii, Quercus chrysolepis, Quercus sadleriana, and Chrysolepis chrysophylla (= Castanopsis chrysophylla). Ericaceous or cold-deciduous shrubs are common, particularly in young or somewhat open stands. Recurrent species include Amelanchier alnifolia, Arctostaphylos patula, Arctostaphylos uva-ursi, Ceanothus velutinus, Gaultheria shallon, Holodiscus discolor, Mahonia nervosa, Mahonia aquifolium (= Mahonia piperiana), Symphoricarpos mollis, Symphoricarpos albus, Quercus vacciniifolia, Toxicodendron diversilobum, Rubus ursinus, and Vaccinium spp. The herb layer is typically dominated by shade-tolerant forbs or ferns, including Pyrola picta, Orthilia secunda, Chimaphila umbellata, Achlys triphylla, Polystichum munitum, Pteridium aquilinum, and Maianthemum stellatum. Graminoids include Bromus vulgaris, Elymus glaucus, and Festuca californica.

In the Sierra Nevada and southern California ranges, these forests form an upper elevation phase of the mixed conifer forests of middle elevations. Abies lowiana is typically dominant, but other conifers commonly present include Pinus ponderosa, Pinus jeffreyi, Pinus lambertiana, Pinus monophylla, Pinus contorta, Calocedrus decurrens, Pseudotsuga menziesii, Abies magnifica var. magnifica, and Abies magnifica var. shastensis (= Abies x shastensis). Common hardwood associates include Cornus nuttallii and Quercus kelloggii. Ericaceous or cold-deciduous shrubs include Arctostaphylos patula, Arctostaphylos nevadensis, Chrysolepis sempervirens (= Castanopsis sempervirens), Ceanothus prostratus, Ceanothus integerrimus, Rubus parviflorus, Prunus emarginata, and Salix scouleriana. On the eastern slope of the Sierra Nevada, Purshia tridentata and Artemisia tridentata may be common. The herbaceous layer is composed largely of forbs, including Asarum hartwegii, Clintonia uniflora, Lupinus latifolius, Adenocaulon bicolor, Sarcodes sanguinea, and Osmorhiza berteroi (= Osmorhiza chilensis).

Dynamics:  These forests are late-seral, ancient forest communities which can persist for very long periods under the present climate. Following low-intensity fire or other disturbance, Pseudotsuga menziesii, or Pinus spp. commonly become established in these communities and can grow to reach the canopy, persisting for centuries. Usually, however these stands occur on sites where fires or other disturbances are rare. In Oregon, the majority of these forests now have closed canopies, where in the past a moderately high fire frequency (20-30 years) formerly maintained an open forest of many conifers. With fire suppression, Abies lowiana tends to replace many of the important conifers at lower elevation sites (Chappell et al. 1997). At higher elevations, the stands are naturally more closed and burn less frequently. Forb, shrub, and wildlife diversity varies greatly with the substrate (Chappell et al. 1997). In California, frequent surface fires restricted these forests to rather moist or less fire-prone areas. With fire suppression, Abies lowiana has vigorously colonized many sites which were formerly occupied by open Pinus ponderosa woodlands. These invasions have dramatically changed the fuel load and potential behavior of fire in these forests. In particular, the potential for high-intensity crown fires has increased. In some areas of the Pacific ranges, hot, stand-replacing fires lead to establishment of dense chaparral thickets which germinate from buried seed. Such stands are highly competitive with coniferous forest species and may slow forest reestablishment.