Rocky Mountains Spruce-Fir Forest

Characteristic of the sub-alpine zone these forests extend from the Mexican border north to the Yukon Territory. The main tree species include the Picea glauca and the two endemic conifers Abies lasiocarpa (Pinaceae) and Picea engelmannii (Pinaceae). The latter is the dominant spruce in southern regions and replaced by Picea glauca in the northernmost Rockies. There are some eight species of Abies with A. religiosa common in the south and A. durangensis becoming more common in the northwest. Nevertheless, these forests are remarkable homogenous throughout the entire length of the Rockies and virgin stands can reach heights of 25 m or more. Other trees include Picea pungens and Populus tremuloides (aspen) in areas where these forests extend to lower altitudes such as in canyons. In the wetter areas trees such as Acer glabrum (rocky mountain maple), Alnus tenuifolia, Salix bebbiana and Sambucus glauca become important components. The shrub layer, particularly on open slopes, is often dominated by species of Vaccinium such as V. myrtillus and the endemic V. scoparium (Ericaceae). Other less frequent shrub layer species include the endemic Sambucus microbotrys (Adoxaceae) and Vaccinium oreophilum (Ericaceae). However, the herb layer is rarely well developed and may be completely absent in some of the more tightly closed forests. Here they tend to be replaced by lichens, fungi and bryophytes. Some of the few more widespread herbaceous species include Arnica cordifolia, Polemonium delicatum and Pyrola secunda, and herbs can become a feature in some of the more open stands particularly where aspen is abundant. Here endemic species such as Erigeron formosissimus (Asteraceae), Lathyrus arizonicus (Fabaceae) and Pseudocymopterus montanus (Apiaceae) may be encountered.

Rocky Mountains Ponderosa Pine Forest

These forests are a common feature of the montane zones particularly in Arizona and New Mexico. The dominant species Pinus ponderosa comprises two varieties. The typical three-needled variety, P. ponderosa var. scopulorum is the most widespread but it is joined by the five-needled variety P. ponderosa var. arizonica in southern Arizona from where it extends southwards into the Sierra Madre. In old growth stands these forests often have a park-like appearance with trees separated by intervening grassy zones. Other locally common trees include Pinus strobiformis, Quercus gambelii and Robinia neomexicana. Under storey shrubs are not particularly common and rarely form dense stands, but there are scattered populations of species such as Berberis repens, Ceanothus fendleri, Holodiscus dumosus, Physocarpus monogynus, Rhus glabra, Ribes aureum, Rosa arizonica, Sambucus cerulea and Symphoricarpos utahensis. In contrast ground layer grasses and sedges are well represented particularly in the more open stands. Typical species include Blepharoneuron tricholepis, Bromus anomalus, Carex geophila, Cyperus fendlerianus, Muhlenbergia montana, Panicum bulbosum, Poa fendleriana, Sitanion hystrix, Stipa pringlei and the endemic Festuca arizonica (Poaceae). Forbs likely to be encountered vary from place to place but include the endemic or near endemic Erigeron flagellaris (Asteraceae), Lathyrus arizonicus (Fabaceae) and Senecio neomexicanus (Asteraceae).

Rocky Mountains Douglas Fir Forest

Forests dominated by Douglas fir (Pseudotsuga menziesii) occur in suitable places throughout most of the montane zones of the Rockies and only absent from the extreme north (northern British Columbia and Yukon). In Colorado’s Front Range they occur on north-facing slopes and steep ravines forming a tree line up to 2700 m in places. Here at these high altitudes it is commonly associated with the shade-intolerant trees Pinus contorta and Pinus ponderosa and in the northwest with Larix occidentalis. In the Alberta ranges forest of Douglas-fir occur on north, south and west facing slopes and on rocky ridges. In the latter associated trees include Pinus albicaulis and P. flexilis. The species composition of the under storey varies from place to place. On north-facing slopes it is often limited to a ground layer of feather mosses, whereas on more open slopes shrubs and grasses predominate. Across the range a number of under storey endemic species occur including graminoids like Carex geyeri (Cyperaceae) and Festuca arizonica (Poaceae) and forbs like Astragalus miser (Fabaceae), Heuchera bracteata (Saxifragaceae) and Ligusticum porteri (Apiaceae).

Rocky Mountains Pygmy Conifer Forest

These rarely exceed about 7 m in height and seem to typically occur on the lower slopes in the transition zone between dry lowland habitat and montane conifer forest. They are usually dominated by juniper and/or dwarf pine species, and occur, for example, on the eastern slopes of the Rockies as far north as central Colorado. Here the dominant species are Juniperus monosperma and Pinus edulis.


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