Physiognomy and Structure: No Data Available

Floristics: The canopy of this type is highly variable, with stands of the southern distribution having a dense canopy of Abies lasiocarpa, with Picea engelmannii a lesser component and Pinus contorta a highly constant seral component. Populus tremuloides is also present sometimes as a seral component. Often these Abies lasiocarpa-dominated stands represent a later successional stage, from which the formerly dominant Pinus contorta has been removed by natural mortality. According to Mauk and Henderson (1984), Abies and Picea are sometimes only poorly represented as stunted or very slow-growing individuals in old-growth stands of persistent Pinus contorta. These prolonged seral conditions typically occur with sites that are not too wet. In the north all degrees of canopy closer have been documented, with the cover usually not greater than 50% and dominated by highly variable combinations of Abies lasiocarpa and Picea engelmannii. Sites are sufficiently wet that Pseudotsuga menziesii and Larix occidentalis do poorly here as seral species, though Pinus contorta may constitute a significant component, its cover often exceeding that of climax dominants. Pfister et al. (1977) report that Pinus albicaulis may occur when this type extends into the upper subalpine zone in protected basins, where it is most commonly found on hummocks or drier sites within the stand. Shrub associates include Ledum glandulosum, Lonicera involucrata, Ribes lacustre, Vaccinium cespitosum, Vaccinium myrtillus, and Vaccinium scoparium. Shrubs characteristic of drier sites may grow on hummocks or at the base of trees (Steele et al. 1983). Rubus parviflorus, Symphoricarpos albus, and Spiraea betulifolia, can comprise a distinct layer in some stands.

The modal undergrowth condition is characterized as a relatively lush sward of Calamagrostis canadensis (or Calamagrostis stricta) with scattered shrubs and herbs. Other graminoids include Carex aquatilis, Carex disperma, Carex microptera (= Carex festivella), Carex norvegica ssp. inferalpina (= Carex media), Luzula parviflora, and Poa reflexa. Associated forbs are geographically variable, and occasionally they can be conspicuous. Those forbs with high constancy at least in the northern portion of this type''s range include Thalictrum occidentale, Senecio triangularis, Veratrum viride, Heracleum maximum, Dodecatheon jeffreyi, Maianthemum stellatum (= Smilacina stellata), Streptopus amplexifolius, and Equisetum arvense. In particular geographic areas Ligusticum spp., Trautvetteria caroliniensis, and Aconitum columbianum can comprise significant cover; other important species include Actaea rubra, Arnica cordifolia, Linnaea borealis, Mertensia ciliata, Mitella pentandra, Osmorhiza depauperata, Pyrola chlorantha, Saxifraga odontoloma (= Saxifraga arguta),and Trollius laxus. Due to the high coverage values for both shrubs and graminoids, the forb component of some sites is negligible (Cooper 1975). Moss cover is typically high.

Steele et al. (1981) and Cooper et al. (1987) recognize four phases for this type in Idaho. The first phase is a Ledum glandulosum phase. It represents the colder or higher extremes of the type, with reduced species richness, Ledum glandulosum forming a dominant undergrowth, and Gaultheria humifusa occurring with a greater frequency than in the other phases. Calamagrostis canadensis becomes increasingly scarce at the upper elevations of this phase. The second phase is a Vaccinium cespitosum phase, representing a frost pocket condition with Pinus contorta a persistent seral dominant. This phase often merges with Abies lasiocarpa/Vaccinium cespitosum on drier sites. The third phase is a Ligusticum canbyi phase which occupies stream terraces and wet benchlands at lower to mid elevations. It has a rich assortment of forbs. Picea is the major seral dominant while Pinus contorta is less abundant than in the other phases. The final phase is a Calamagrostis canadensis phase occurring at low to mid elevations and exhibiting the typic conditions for this association.

Steele et al. (1983) recognize three phases for this type in western Wyoming. The first, a Ledum glandulosum phase, represents the cool extreme of the type. The second, a Vaccinium cespitosum phase, indicates a frost pocket condition. The last phase is a Calamagrostis canadensis phase, representing the typic conditions of the association.

Pfister et al. (1977) recognize three phases for this type in Montana. This first phase, a Calamagrostis canadensis phase, represents the typic conditions of the type. The second, a Galium triflorum phase, represents the type at its lower elevational limits where it is transitional to warmer habitat types such as Abies lasiocarpa/Galium triflorum or Picea/Equisetum arvense. The third phase, a Vaccinium cespitosum phase, is also associated with the lower elevations of the type, but on drier sites and is transitional to the Abies lasiocarpa/Vaccinium cespitosum type.

Abies lasiocarpa/Calamagrostis canadensis occupies the lowest, most poorly drained sites, and is found near Abies lasiocarpa/Vaccinium scoparium and Abies lasiocarpa/Menziesia ferruginea on adjacent better drained sites (Pfister et al. 1977). Abies lasiocarpa/Calamagrostis canadensis can be found merging on the wet end of its moisture spectrum with marshes, sedge-dominated meadows, and pond margins, and on the dry side with various Pseudotsuga associations (Cooper 1975).

Dynamics:  This type is not so constantly moist as to prevent burning as indicated by the predominance of Pinus contorta (Cooper 1975). Fischer and Bradley (1987) place this association in their fire group nine, except for the drier Abies lasiocarpa/Calamagrostis canadensis, Vaccinium cespitosum phase which is in fire group seven. Fire group nine represents the moist, lower subalpine habitat types with infrequent but severe fires of long-lasting effect. The combination of deep duff and large amounts of dead rotten fuel can result in severe surface fire during unusually dry moisture conditions such as late-summer droughts. Where dense understories exist, such fires can easily spread to the tree crowns and destroy the stand. Even if a severe surface fire does not crown, there is a good chance the overstory trees will be killed by cambium heating. Under normal moisture conditions for these sites, a lush undergrowth of shrubs and herbs usually serves as an effective barrier to rapid fire spread.