Southern Rocky Mountains Ecoregion

Physiography

The eastern flank of the Southern Rocky Mountains ecoregion, with a rapid elevation gain of nearly 9,800 ft, is an impressive sight for travelers heading west across the eastern plains. Elevation ranges from 3,746 ft near Orchard Mesa in Mesa County, Colorado to 14,431 ft on Mt. Elbert in Lake County, Colorado. Colorado encompasses 73.5% of the ecoregion, New Mexico 18%, and Wyoming 8.5%. Glacial activity and resulting meltwaters have shaped much of the ecoregion into high rugged mountains, plateaus, alpine cirques, glacial moraines, and broad valleys. Colorado contains the highest summits in the entire Rocky Mountain system, with 54 mountains exceeding 14,000 ft and 300 peaks over 13,000 ft. The SRM is the highest ecoregion in North America, based on average elevation (9,670 ft) and amount of land above 10,000 ft. Other notable topographic features include hogbacks, mesas, and rocky outcrops where the high mountains meet the plains on the eastern front, and rugged canyons and mesas where the mountains meet the high desert country to the west.

Climate

The topographic relief of the Rocky Mountains dominates the climatic variability of the Southern Rocky Mountain ecoregion. The climate is a temperate semiarid steppe regime with average annual temperatures ranging from 35°F to 45°F in most of the ecoregion, but reaching 50°F  in the lower valleys. Prevailing west winds and general north-south orientation of the mountain ranges also influence the climate. Late summer monsoonal patterns also influence the southern portion of the ecoregion. Eastern slopes are generally much drier than west slopes, and more than 75% of the precipitation falls west of the Continental Divide. Winter precipitation varies considerably with elevation. In the highest mountains, a considerable part of the annual precipitation falls as snow, although permanent snowfields and glaciers cover relatively small areas. More precipitation falls as winter snow than as summer rain in the western mountains whereas winter and summer precipitation is about the same on the Eastern Slope. Annual rainfall ranges from under 10 inches at the base of the mountains in the San Luis Valley to over 55 inches at higher elevations in the Park Range. The mountain parks and valleys are cooler and drier than the surrounding mountains, as they lie in the rain-shadow of the mountains and trap cold-air masses for long periods.

Plants & Animals

At least 184 species and subspecies are known to be endemic to the ecoregion, meaning they occur in the SRM and are not known from anywhere else in the world. The richest known groups of species are plants (118 endemics) and invertebrates (51 endemics), followed by mammals (12 endemics), birds (2 endemics), and amphibians (1 endemic). Examples of these endemic species include the Penland penstemon (Penstemon penlandii), Uncompahgre fritillary butterfly (Boloria improba acrocnema), Goat Peak pika (Ochotona princeps nigrescens), Jemez Mountains salamander (Plethodon neomexicanus), and brown-capped rosy finch (Leucosticte australis). The relative ecological isolation of the SRM, significant climate changes in the recent geological past, and the ecoregion’s complex topographic and geologic features provide fertile ground for evolutionary change that often results in high endemism. The area is known for its high species richness in butterflies and moths, mammals, birds, and several plant groups (e.g., Penstemon, Eriogonum, and Astragalus). In the lower 48 states, only southeast Arizona has a higher species diversity for invertebrates, particularly butterflies and moths, than the lower foothills of Colorado’s Front Range. There are also a large number of disjunct boreal species at the southern end of their range in the SRM, such as Greenland primrose (Primula egaliksensis). New taxa are still being described from the ecoregion, e.g., the Gunnison sage grouse (Centrocercus minimus) and several moths (Grammia, Gazryctra, Lycia). Scientists believe that there are a number of other species not yet described, particularly invertebrates and fungi.

Today

Although the ecoregion contains largely intact or functional landscapes, a number of species in the SRM are either extinct or extirpated. At least three vertebrates of the SRM are known to be extinct: the yellowfin cutthroat trout (Oncorhynchus clarki macdonaldi), which formerly occurred in the upper reaches of the Arkansas River; Carolina parakeet (Conuropsis carolinensis), which formerly occupied Colorado’s Great Plains and foothills as far west as Salida; and the New Mexico sharp-tailed grouse (Tympanuchus phasianellus hueyi). Several invertebrate species are believed to be extinct (Kondratieff and Opler, unpublished data), including what was once one of the most abundant insects, the Rocky Mountain locust (Melanoplus spretus). In addition, a number of species have been extirpated from the ecoregion, including seven mammal species: grizzly bear (Usus arctos), gray wolf (Canis lupus), wild populations of bison (Bison bison), black-footed ferret (Mustela nigripes), lynx (Felis lynx canadensis), wolverine (Gulo gulo), and river otter (Lutra canadensis). Black-footed ferret, lynx, and river otter have recently been brought back into the ecoregion through restoration efforts. Eight fishes are extirpated from the ecoregion, including the Rio Grande bluntnose shiner (Notropis simus simus), Rio Grande silvery minnow (Hybognathus amarus), American eel (Anguilla rostrata), freshwater drum (Aplodinotus grunniens), shovel nose sturgeon (Scaphirhynchus platorynchus), blue sucker (Cycleptus elongatus), Rio Grande shiner (Notropis jemezanus), and speckled chub (Extrarius aestivalis).

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