Rocky Mountains Alpine Tundra

In the Uinta Mountains of the Central Rockies, alpine tundra is a major feature at altitudes over about 3300 m and extends for some 780 km2. In the more exposed areas the vegetation is characterized by a variety of cushion plants, such as Silene acaulis, the rock sedge Carex rupestris and the endemic Paronychia pulvinata (Caryophyllaceae). Most of the flowering plants are low growing, but it has been suggested that what they lack in stature they more than make up for in dazzling colours. On Beartooth Mountains also in the Central Rockies the tundra cushion plants typically include Kobresia myosuoides and the endemic Phlox caespitosa (Polemoniaceae). These stands also support a number of local endemic taxa such as Aquilegia jones, Delphinium glaucescens (Ranunuculaceae), Erigeron gracilis, E. rydbergii (Asteraceae), Salix rotundifolia var. dodgeana (Salicaceae) and Trifolium haydenii (Fabaceae). In the southern Rockies (Colorado and New Mexico) alpine tundra mainly exists as small, isolated stands above about 3500 m. Low mat and cushion forbs again characterize the vegetation while other typical forbs include Achillea lanulosa, Potentilla nivea and the endemic Androsace carinata (Primulaceae), Claytonia megarrhiza (Portulacaceae), Primula angustifolia (Primulaceae), Pseudocymopteris montanus (Apiaceae) and Trifolium nanum (Fabaceae). Grasses are also well represented and some patches could be described as alpine grassland. Typical species include Deschampsia caespitosa, Festuca ovina var. brachyphylla and blue grasses like Poa arctica, P. glauca and the endemic P. reflexa and P. rupicola (Poaceae). Carex is an important component often intermingled with grasses. The more important species include Carex ebenea, C. foena, C. nova and the endemic C. petasata and C. scopulorum (Cyperaceae). These tundra plants are well adapted to the cold, harsh upland climate. Many, for example, have a thick insulating coat of hairs and a number can photosynthesis at temperatures close to freezing. At altitudes below tundra in several parts of the Rockes there is often an interesting transition zone to the sub-alpine forests known as the Krommholz which is characterized by dwarf forms of spruce and fir that often have twisted trunks leaning away from the prevailing winds. In the northern Rockies, such as in the Alberta Range, this zone can be as low as 1500 m.

Rocky Mountains Alpine Meadow

Surprisingly sedges are often more prevalent than grasses in these alpine meadows. The sedge genus Carex is particularly well represented with species such as C. aurea, C. brevipes, C. elynoides, C. engelmannii, C. festivella, C. haydeniana, C. microptera, C. phaeocephala, C. praeceptorum, C. pseudoscirpoides, C. rupestris, C. scirpoides and the endemic C. arapahoensis, C. bella, C. chalciolepis and C. obtusata (Cyperaceae). Typical grasses may include Agropyron trachycaulum, Agrostis idohoensis, Avenochloa hookeri, Helictotrichum mortonianum, Kobresia myosuroides, Phleum alpinum, Trisetum spicatum and the endemic Festuca hallii and F. thunberi (Poaceae). At ground level, lichens and mosses commonly grow between the tussocks, but it is the multitude of colourful forbs that make these meadows so special. Most bloom in midsummer when colours can reach a magnificent crescendo. Characteristic species may include Anemone narcissiflora, Antennaria alpina, Arabis lemmonii, Arenaria conjesta, Aster alpinus, Bupleurum americanum, Campanula parryi, Cerastium beeringianum, Comandra pallida, Draba aurea, Erigeron aureus, Eritrichium aretioides, Gentiana algida, Lloydia serotina, Melandrium apetalum, Myosotis alpestris, Nothocalais alpestris, Oxytropis cusickii, Pedicularis thompsonii, Polemonium viscosum, Potentilla brevifolia, Pulsatilla occidentalis, Ranunculus pedatifidus, Saxifraga laeta, Taraxacum ceratophorum, Thalictrum alpinum, Valeriana edulis, Viola adunca, Zygadenus elegans and the endemic Artemisia borealis (Asteraceae), Aster coloradensis (Asteraceae), Besseya ritteriana (Scrophulariaceae), Castilleja occidentalis (Orobanchaceae), Draba spectabilis (Brassicaceae), Erigeron ursinus (Asteraceae), Erysimum amoenum (Brassicaceae), Gentiana barbellata (Gentianaceae), Hymenoxys grandiflora (Asteraceae), Podistera eastwoodii (Apiaceae), Potentilla quinquifolia (Rosaceae), Primula angustifolia (Primulaceae) and Townsendia rothrockii (Asteraceae). Pteridophytes, on the other hand, are far less prominent. The two main species likely to be encountered are Botrychium lunaria ssp. minganense and Selaginella densa.

Rocky Mountains Alpine-Montane Wet Meadow

Ranging in elevation from montane to alpine (1000-3600 m) these wet meadows are found throughout the Rockies. At montane level they typically occur in flattish zones or on gentle slopes, while in alpine regions they are usually found in small depression located below late-melting snow or on snow beds. The vegetation often forms a mosaic of several plant associations but usually comprises a dense layer of graminoids characterized by Agrostis scabra, Calamagrostis canadensis, Carex aquatilis, C. microptera, C. nebrascensis, C. pellita, C. praegracilis, C. stricta, C. utriculata, Deschampsia cespitosa, Eleocharis palustris, Juncus balticus var. montanus, J. drummondii, Scirpus pungens and the endemic Carex scopulorum (Cyperaceae). Forbs have a more scattered distribution but typically include Geum macrophyllum, Parnassia fimbriata, Pedicularis groenlandica, Polemonium caeruleum, Polygonum bistortoides, Rorippa alpina, Senecio triangularis, Symphyotrichum foliaceum, S. spathulatum, Veronica americana and the endemic Caltha leptosepala (Ranunculaceae) and Trifolium parryi (Fabaceae). However, where there as been excessive grazing, species such as Argentea anserina, Dasiphora floribunda, Iris missouriensis and Juncus arcticus become disproportionately abundant.

Rocky Mountains Subalpine-Montane Fen

Mountain fen vegetation is not a common feature of the Rockies but can be found in scattered location from Colorado north to Canada. They require relatively base-rich conditions with minerals such as calcium and magnesium in good supply, but can develop on both peat and perennially saturated soils. The vegetation is largely dominated by graminoids particularly Carex aquatilis, C. lasiocarpa and C. utriculata. Other common ones are Carex buxbaumii, C. simulata, Deschampsia cespitosa, Eleocharis quinqueflora and the endemic grass Poa leptocoma (Poaceae).  Forbs, othe other hand, are more sparsely distributed and include many of the species associated with wet meadows. Others examples include Packera pseudaurea and Rhodiola rhodantha. In places shrubs become important to form so-called ‘carr’. Typical species are Betula nana, Salix planifolia and the endemic Salix wolfii (Salicaceae). In areas of high pH so-called rich or species-rich fen occurs. These tend to be dominated by sedges such as Kobresia myosuroides and K. simpliciuscula. Also found here are various rare or uncommon species like Carex livida, Primula egaliksensis, Ptilagrostis mongholica ssp. porteri, Salix myrtillifolia, Sisyrinchium pallidum, Trichophorum pumilum and Utricularia pumilum. Other interesting fen types include the so-called iron fens as exemplified by Emmon Iron Fen in Gunnison County. These occur in areas where the ground water percolates through rock rich in pyrite. This oxidizes producing sulfuric acid, which leaches cations from any associated bedrock creating nutrient rich, but acidic ground water. In places iron precipitates out of solution and then solidifies into hard rock. Typical iron fen species include trees such as Pinus contorta and Picea engelmannii, and shrub such as Gaultheria humifusa and Vaccinium cespitosa in a carpet of mosses.

Rocky Mountains Talus and Scree Slopes

Here talus is defined as comprising fist-sized rocks or larger while scree is regarded as having smaller rocks down to gravel size. Most plant species can only colonize these slopes when they have a degree of stability and scree can be particularly unstable. However, one species in particular, Dryas octopetala ssp. hookerian, can colonize relatively unstable scree and then once established creates a stabilizing influence. It also helps in the soil building process, which is no doubt assisted by its ability to fix nitrogen. Like legumes and alders, Dryas has root nodules containing nitrogen-fixing bacteria. Other species found associated with scree include Antennaria lanata, Carex proposita, Chaenactis alpina, Collomia debilis, Crepis nana, Eriogonum piperi, Lewisia nevadensis, Lupinus alpestris, Mimulus suksdorfii, Phoenicaulis cheiranthoides, Physaria alpestris, Potentilla fruticosa, Ranunculus verecundus, Saxifragus flagellaris, Senecio werneriaefolius, Smelowskia calycina, Solidago decumbens and the endemic Astragalus molybdenus (Fabaceae), Delphinium alpestrs (Ranunculaceae), Penstemon hallii (Plantaginaceae), Phacelia glandulosa (Boraginaceae), Senecio taraxacoides (Asteraceae) and Taraxacum phymatocarpum (Asteraceae). Species more typical of talus slopes include Carex straminiformis, Dicentra uniflora, Douglasia nivalis, Draba crassa, Epilobium clavata, Erigeron vagus, Haplopappus macronema, Hulsea algida, Poa gracillima, Senecio fremontii, Silene parryi, Townsendia leptotes and the endemic Draba graminea (Brassicaceae), Lesquerella alpina (Brassicaceae), Mertensia alpina (Boraginaceae) and Oreoxis bakeri (Apiaceae).

Rocky Mountains Snow Bed Communities

So-called snow bed vegetation is characteristic of areas where snow lasts late in to the summer. By the time the snow eventually melts much of the other alpine vegetation is in full bloom whereas the snow bed plants are just starting to develop. In fact, after heavy snows followed by a cool summer some plants may remain covered throughout the summer. Even where snow disappears soil temperatures are often kept low by the proximity of permafrost and topsoil becomes initially saturated by melt water. It comes as no surprise therefore that most snow bed plant species are especially adapted to these conditions and have to undergo rapid development. On the other hand, snow cover provides protection in winter with temperatures below the snow being considerable higher than air temperatures, and there is much less diurnal variation. Snow bed vegetation is typically composed of concentric rings since snow usually melts from the outer edges inwards lasting progressively longer towards the centre. In the Rockies the typical zonation pattern includes an out ring composed of willows possibly including species such as Salix arcticus, S. cascadensis or S. nivalis (snow willow) followed by a ring of grasses like Agrostis borealis, A. humils, Poa arctica or the endemic Poa reflexa (Poaceae). Inside the grass ring a zone typically dominated by Sibbaldia procumbens is likely to be present. This species, which is also found in Northern Europe, is a classic indicator of snow beds. A ring of rushes possibly including Juncus drummondii, J. mertensianus or J. parryi typically occurs inside the Sibbaldia zone and this is followed by a central area of sedges which have to endure the shortest snow-free period. These may include Carex humilis, C. incurviformis or C. spectablis. However, this is a fairly idealized pattern and likely to vary considerable in reality. Other obligate or near obligate snow bed plants found here include Agoseris aurantiaca, Armeria maritima ssp. labradorica, Artemisia arctica subsp. saxicola, Aster foliaceus var. apricus, Braya humilis, Draba crassifolia, Erythronium grandiflorum, Hieracium gracile, Lewisia pygmaea, Lycopodium obscurum, Minuartia biflora, Phyllodoce empetriformis, Pulsatilla ludoviciana, Ranunculus eschscholtzii, Trifolium stenolobum, Vahlodea atropurpurea and the endemic Erigeron leiomerus (Asteraceae), Luzula subcapitata (Juncaceae), Ranunculus macauleyi (Ranunculaceae), Saussurea weberi (Asteraceae) and Senecio dimorphophyllus (Asteraceae).


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