Physiognomy and Structure: No Data Available

Floristics: This association is characterized by a moderately dense to dense, mixed evergreen-deciduous tree canopy that is codominated by Populus tremuloides and Abies concolor. Abies lasiocarpa is typically not present, but individuals of Pseudotsuga menziesii, Picea engelmannii, Picea pungens, or Pinus ponderosa are not uncommon. Often the conifers form a subcanopy that will eventually overtake the Populus tremuloides in this early seral type. Symphoricarpos oreophilus is the characteristic species of the short-shrub layer and typically dominates. Associates include several other common species in lesser amounts such as Amelanchier spp., Arctostaphylos patula, Mahonia repens, Juniperus communis, Paxistima myrsinites, and Rosa woodsii. The moderately dense herbaceous layer is usually luxuriant and species-rich in comparison to adjacent conifer forests because light is able to penetrate the Populus tremuloides tree canopy. Herbaceous species are diverse and variable. Common graminoids are Achnatherum occidentale, Bromus anomalus, Bromus carinatus, Carex geyeri, Carex rossii, Elymus glaucus, Elymus trachycaulus, Festuca arizonica, Poa fendleriana, and Poa nervosa. Forbs may include Achillea millefolium, Eucephalus engelmannii, Frasera speciosa, Geranium spp., Lathyrus spp., Rudbeckia occidentalis, Osmorhiza berteroi (= Osmorhiza chilensis), and Thalictrum fendleri. The introduced graminoids Poa pratensis and Dactylis glomerata are common in many stands.

Dynamics:  Abies concolor is much more shade-tolerant than Populus tremuloides and is the most important regenerating species under closed-canopy conditions. Most of these mixed stands are seral, in the absence of fire will eventually be dominated by Abies concolor. This unique forest alliance is linked to gap-forming disturbances, such as fire or windthrow, which allow regeneration of Populus tremuloides and limit abundances of Abies concolor (Mueggler 1988, Mueggler and Campbell 1986).