South Central Rockies forests
The South Central Rockies forests is a set of seven disjunctive geographic units, forming an ecoregion centered primarily on the Yellowstone Plateau and the mountain ranges radiating outward from the plateau. The largest unit lies mainly in western Wyoming, extending into eastern Idaho and central Montana; a portion of this ecoregion lies in northwestern Wyoming, and comprises the headwaters of the Yellowstone River and Green River. A second large unit comprises the mountains of central and eastern Idaho south of the Clearwater River. The ecoregion also occurs in five additional isolated geographic units, the two largest being the Bighorn Mountains of north-central Wyoming/ south-central Montana, and the Black Hills of western South Dakota/ northeastern Wyoming.
Location and general depiction
The ecoregion is characterized by dramatic vertical zonation of vegetation and associated fauna. This zonation is a consequence of abrupt elevational gradients between flatlands and mountains. Topographic relief is quite dramatic; for example, the Bighorn Mountains rise 2794 meters above the surrounding lowlands. The range of biotic zones is greater at the higher elevations (e.g., Wind River and Teton Ranges in Wyoming; Madison Range in Montana). Secondary climatic effects of topographic relief (e.g., rain-shadow effects, exposure to or shelter from prevailing winds, and thermal inversions) likewise influence zonation.
The Black Hills unit of the ecoregion, being the lowest in elevation and having relatively gentle topographic relief, exhibits the least amount of zonal variation. This unit has distinctive floristic diversity, however, containing flora representative of Great Basin, Eastern Deciduous, Boreal, Rocky Mountain, and Southern Great Plains.
Relative to other Rocky Mountain ecoregions, the South Central Rockies is dry, experiencing a predominantly continental climate. Summers are brief and winters long and cold. Significant precipitation occurs in the higher elevations, typically as snow.
The dominant vegetation type in the ecoregion is coniferous forest. Küchler classifies the potential vegetation type as Douglas-fir / spruce-fir forest, dominated by Engleman spruce (Picea englemannii), subalpine fir (Abies lasiocarpa), and Douglas-fir (Psuedotsuga menziesii). As Peet lectures, however, most forests in the Rocky Mountains "are in some stage of recovery from prior disturbance . . .climax stands [are] less common than seral communities." Thus, instead of one or all of the expected fir species, large areas of the ecoregion are dominated by Lodgepole pine. In some regard, the preponderance of Lodgepole pine reflects the greatly altered (via fire suppression) disturbance regime in the ecoregion. Whitebark pine (Pinus albicaulis) is an important species at the upper treeline / Krummholz zone.
In addition to expansive conifer forests, the ecoregion contains several other vegetation communities. Mountain meadows, foothill grasslands, riparian woodlands, and upper treeline / alpine communities exist throughout the ecoregion. In the Yellowstone unit, unique biotic communities occur in association with geothermal features (e.g. geysers, hot springs), due to the unique micro-environments formed by varying soil chemical composition and warm temperatures.
Fire, snow avalanche, seismic disturbance, and wind are chief disturbance factors in this ecoregion. Prevailing winds alter distribution and morphology of tree species at higher elevations, while periodic "blowdown" events can topple hundreds of acres of mature forest in one high wind event. These blown-down areas in turn can fuel stand-replacing fires during dry seasons. Herbivory is also a significant influence, particularly in aspen and riparian willow communities.
There are 318 recorded vertebrate species in the South Central Rockies forests, indicating a modest degree of faunal species richness. Furthermore, there are a number of special status taxa that are found on the South Central Rockies forests, denoted variously as Near Threatened (NT), Vulnerable (VU), Endangered (EN), or Critically Endangered (CR).
The American bison (Bison bison NT) is the premier example of charismatic megafauna within the South Central Rockies forests and is an ecoregion endemic. The Yellow-bellied marmot (Marmota flaviventris) is also found here in its colonial burrows, especially at mountain meadow and talus habitats. American black bear (Ursus americanus) and Grizzly bear (Ursus arctos horribilis) also occur within the ecoregion. In addition to these ursine species, two other apex predators in these forests are the Bobcat (Lynx rufus) and Canadian lynx (Lynx canadensis). Other mammals found here are the American mink (Neovison vison) and the Black-tailed prairie dog (Cynomys ludovicianus); and the Western harvest mouse (Reithrodontomys megalotis).
There are only six amphibian taxa known to the South Central Rockies forests. Anuran species found in the ecoregion are: Northern leopard frog (Lithobates pipiens); Boreal chorus frog (Pseudacris maculata); Columbia spotted frog (Rana luteiventris); Woodhouse's toad (Anaxyrus woodhousii); and Western toad (Anaxyrus boreas). Salamanders found here in the South Central Rockies forests are merely the Tiger salamander (Ambystoma tigrinum).
Pituophis catenifer); and the Smooth green snake (Liochlorophis vernalis).Notable reptiles that can be observed in the South Central Rockies forests include: Painted turtle (Chrysemys picta); Ornate tree lizard (Urosaurus ornatus); Western rattlesnake (Crotalis viridis); Western terrestrial garter snake (Thamnopsis elegans); Red-bellied snake (Storeria occipitomaculata); Western gopher snake (
Avifauna found in the ecoregion include the Golden eagle (Aquila chrysaetos); Pinyon jay (Gymnorhinus cyanocephalus VU); Lapland longspur (Calcarius lapponicus); Blue-grey gnatcatcher (Polioptila caerulea); Black-backed woodpecker (Picoides arcticus); and the Golden-crowned kinglet (Regulus satropa).
Habitat loss and degradation
Logging, hard-rock mining, oil and gas development, and recreational-residential construction are all major anthropogenic pressures on the ecoregion. Domestic livestock overgrazing and spread of exotic species are altering species compositions. Potential expansion of recreational use of remote areas is further adversely affecting the ecoregion; however, note that Yellowstone use grew vigorously from 1904 to 1992 and has somewhat leveled off through 2014.
Remaining blocks of intact habitat
Many of the ecoregion's mountain ranges are still relatively intact, although most have been altered somewhat by historic mining, logging, overgrazing, overhunting of megafauna, and overly aggressive fire suppression. The higher mountains in and immediately adjacent to Yellowstone National Park have seen some human influence in the last century, but minor compared to more accessible portions of the ecoregion.
The following elements are largely intact:
- The Frank Church Wilderness - central Idaho
- the Lemhi and Lost River Ranges - eastern Idaho
- the Beaverhead - southwestern Montana
- Anaconda-Pintler - southwestern Montana
- Pioneer - southwestern Montana
- Tobacco Root - southwestern Montana
- Snowcrest - southwestern Montana
- Centennial - southwestern Montana
- Madison Ranges - southwestern Montana
The following units are mostly intact:
- The Bridger - south-central Montana
- Big Belt - south-central Montana
- Little Belt - south-central Montana
- Crazy Mountains - south-central Montana
However, these areas show the effects of being isolated ranges near large population centers. Mountains to the south of Yellowstone National Park, including the Wind River, Wyoming, and Salt River Ranges, are rugged, remote, and relatively intact.
Degree of fragmentation
Intensive development in valley bottoms, combined with existing transportation corridors, is beginning to disrupt connectivity within the ecoregion. Low elevation development (often in Küchler ecoregions 57, 75, and 77) has eliminated winter range or blocked off migratory routes for ungulates. Massive clearcuts, particularly on the Targhee National Forest, have similarly caused fragmentation. Development of the high alpine environment has been limited, with notable exceptions of four major downhill ski resorts throughout this higer elevation area.
Degree of protection
The degree of protection in the ecoregion is fairly high, relative to some other Rocky Mountain ecoregions. Parks such as Yellowstone and Grand Teton embrace a broad elevational and climatic gradient. Combined with adjacent wilderness areas, they form large blocks of protected habitat for many species. More work, however, still lies ahead to meet the needs of wider ranging species like grizzly bears and wolves.
Type and severity of threats
Indiscriminate logging, especially associated road-building, are major problems. Existing road networks in non-wilderness areas are unnecessarily dense and contribute to an overall loss of habitat security. Rapid development of low elevation areas is another threat, although concentrated mainly in other ecoregions. Mortality to grizzly bears and possibly to wolves through ungulate hunters in the autumn is unacceptably high, and could be making the difference between a growing and a declining grizzly population in Greater Yellowstone.
Measures to enhance biodiversity conservation
- Identifying and maintaining critical linkage habitats within the ecoregion and among other ecoregions is vital to enhance biological corridors.
- Below market grazing lets should be eliminated.
- New forest roads should be discouraged, with seasonal closures and obliteration projects implemented to reduce motorized access.
- Visitor/recreation in parks and wildernesses should be diminished by economic means. Yellowstone National Park should consider abandoning and obliterating part of its extensive paved road network.
- Alliance for the Wild Rockies
- American Wildlands
- Craighead Environmental Research Institute
- Craighead Wildlife-Wildlands Institute
- Defenders of Wildlife
- The Great Bear Foundation Greater Yellowstone Coalition
- Montana Wilderness Association
- Northern Rockies Conservation Co-op
- Northern Rockies Conservation Co-op
- Predator Project
- Wild Forever
- The Wilderness Society, Northern Rockies Regional Office
- The Yellowstone Institute
- Wyoming Outdoor Council
- Yellowstone Ecosystem Studies
Relationship to other classification schemes
This ecoregion closely matches Omernik's Middle Rockies, with the addition of the Frank Church Wilderness unit and the mountain ranges to the south and east of the Frank Church unit. It corresponds approximately to Bailey's M331A, D, E, and J. Bailey does not include the Black Hills as part of this ecoregion. Küchler classifies this ecoregion as numbers 11, 14, 16, 45, and 49 in the Küchler scheme.
- North Central Rockies forests, to the north
- Montana valley and foothill grasslands, to the north-northeast
- Northern short grasslands, to the northeast
- Wyoming basin shrub steppe, to the east and south
- Snake-Columbia shrub steppe, to the southwest
- Blue Mountains forests, to the west
- Palouse grasslands, to the northwest
- John Byrd, Robert Smith and John Geissman. 1994. The Teton fault, Wyoming: Topographic signature, neotectonics, and mechanisms of deformation. Journal of Geophysical Research. B10 99: 20,095–20,122
- Sara Dant. 2008. Making Wilderness Work: Frank Church and the American Wilderness Movement. Pacific Historical Review 77: 237–272
- Cynde Georgen. 2010. In the shadow of the Bighorns: A history of early Sheridan and the Goose Creek valley of northern Wyoming. Sheridan, Wyoming: Sheridan County Historical Society, 2010. ISBN 978-0-9792871-7-6
- C. Michael Hogan. 2012. Yellow-bellied marmot: species abstract. Encyclopedia of Life
- James R. Steidtmann; Larry Middleton and T. Larry. "Post-Laramide (Oligocene) uplift in the Wind River Range, Wyoming". Geology (The Geological Society of America) 17 (1): 38–41.
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