Ecoregions of Idaho (EPA)
Ecoregions denote areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources; they are designed to serve as a spatial framework for the research, assessment, management, and monitoring of ecosystems and ecosystem components. By recognizing the spatial differences in the capacities and potentials of ecosystems, ecoregions stratify the environment by its probable response to disturbance (Bryce and others, 1999). These general purpose regions are critical for structuring and implementing ecosystem management strategies across federal agencies, state agencies, and nongovernment organizations that are responsible for different types of resources within the same geographical areas (Omernik and others, 2000).
The approach used to compile this map is based on the premise that ecological regions can be identified through the analysis of the spatial patterns and the composition of biotic and abiotic phenomena that affect or reflect differences in ecosystem quality and integrity (Wiken, 1986; Omernik, 1987, 1995). These phenomena include geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology.
The relative importance of each characteristic varies from one ecological region to another regardless of the hierarchical level. A Roman numeral hierarchical scheme has been adopted for different levels of ecological regions. Level I is the coarsest level, dividing North America into 15 ecological regions. Level II divides the continent into 52 regions (Commission for Environmental Cooperation Working Group, 1997). At level III, the continental United States contains 104 ecoregions and the conterminous United States has 84 ecoregions (United States Environmental Protection Agency [USEPA], 2000). Level IV is a further subdivision of level III ecoregions. Explanations of the methods used to define the USEPA’s ecoregions are given in Omernik (1995), Omernik and others (2000), Griffith and others (1994), and Gallant and others (1989).
Idaho is made up of semiarid shrub- and grass-covered plains, irrigated agricultural valleys, volcanic plateaus, forested mountains, woodland- and shrubland-covered hills, glaciated peaks, lava fields, and wetlands. Ecological diversity is enormous. There are 10 level III ecoregions and 71 level IV ecoregions in Idaho and many continue into ecologically similar parts of adjacent states.
The level III and IV ecoregion map on this poster was compiled at a scale of 1:250,000 and depicts revisions and subdivisions of earlier level III ecoregions that were originally compiled at a smaller scale (USEPA, 2000; Omernik, 1987). This poster is part of a collaborative project primarily between USEPA Region X, USEPA National Health and Environmental Effects Research Laboratory (Corvallis, Oregon), Idaho Division of Environmental Quality (IDEQ), United States Department of Agriculture–Forest Service (USFS), United States Department of Agriculture–Natural Resources Conservation Service (NRCS), United States Department of the Interior–Bureau of Land Management (BLM), and United States Department of the Interior–Geological Survey (USGS)–Earth Resources Observation Systems (EROS) Data Center.
The project is associated with an interagency effort to develop a common framework of ecological regions. Reaching that objective requires recognition of the differences in the conceptual approaches and mapping methodologies applied to develop the most common ecoregion-type frameworks, including those developed by the USFS (Bailey and others, 1994), the USEPA (Omernik, 1987, 1995), and the NRCS (U.S. Department of Agriculture–Soil Conservation Service, 1981). As each of these frameworks is further refined, their differences are becoming less discernible. Regional collaborative projects such as this one in Idaho, where agreement has been reached among multiple resource management agencies, are a step toward attaining consensus and consistency in ecoregion frameworks for the entire nation.
|10. Columbia Plateau |
Ecoregion 10 is an arid grassland and sagebrush steppe that is surrounded by moister, predominantly forested, mountainous ecoregions. It is underlain by thick basalt. In the east, where precipitation is greater, deep loess soils have been extensively cultivated for wheat.
|10f. The unforested hills and plateaus of the Dissected Loess Uplands ecoregion are cut by the canyons of Ecoregion 10l and are disjunct. Pure grasslands dominate lower elevations. Mountain brush grows on higher, moister sites. Grazing and farming have eliminated much of the original plant cover. Nevertheless, Ecoregion 10f is not as suited to farming as Ecoregions 10h and 10j because it has thinner soils.|
10h. The largely unforested, loess-covered Palouse Hills ecoregion abuts the Rocky Mountains and has more available moisture than other parts of Ecoregion 10. Mountain fed perennial streams occur and intermittent, loess-bottomed streams rise within Ecoregion 10h. Soils, rich in organic matter and very productive, support extensive wheat farming but are easily eroded. Dry stream channels may be tilled.
10j. The Nez Perce Prairie is a loess-covered plateau. It is higher, cooler, less hilly, and has shallower soils than Ecoregion 10h. Idaho fescue and bluebunch wheatgrass are native. Cropland is now extensive and grows wheat, barley, peas, and hay. The headwaters of many perennial streams are impacted by agricultural land use, negatively impacting the water quality of downstream canyon reaches.
10l. The Lower Snake and Clearwater Canyons cut through the basalts of the Columbia Plateau (10). Canyon depths exceed 1,400 feet and create drier conditions than in Ecoregions 10f or 10h; mean annual precipitation is only 12 to 25 inches. Outside of towns and transportation corridors, Ecoregion 10l's canyons provide good habitat for bighorn sheep and game birds.
|11. Blue Mountains |
Ecoregion 11 is a complex of mountain ranges that are lower and much more open than the neighboring Cascades (4) and Northern Rockies (15). Like the Cascades (4), but unlike the Northern Rockies (15) and the Idaho Batholith (16), the Blue Mountains (11) is mostly volcanic in origin. Only its highest ranges, particularly the Wallowa and Elkhorn mountains in Oregon, consist of intrusive rocks that rise above the dissected lava surface of the region. Much of Ecoregion 11 is grazed by cattle in contrast to Ecoregions 4 and 15.
|11d. The dissected mountains of the Melange ecoregion are mostly blanketed in Tertiary basalt but have a core of mixed metamorphic, metavolcanic, metasedimentary, and sedimentary rocks. Forests dominated by Douglas-fir, ponderosa pine, and lodgepole pine, as well as shrublands and grasslands occur. Lithology affects soil, vegetation, and the quantity and quality of surficial water. Grazing is common but logging is limited by the difficulty of reforesting droughty soils such as those that are derived from metamorphic rocks. |
11e. In Idaho, the Wallowas/Seven Devils Mountains ecoregion ranges in elevation from about 4,000 to 9,200 feet. Lowest elevations support a dry forest community. Douglas-fir and ponderosa pine forests are widespread and have a shrub understory. Streams follow fault lines, have steep gradients and have eroded deep canyons. Land uses include grazing, logging, recreation, and wildlife habitat.
11f. The Canyons and Dissected Highlands ecoregion includes the southern Seven Devils Mountains and pieces of the uplifted Columbia Plateau. Elevations range from 4,000 to 6,400 feet. Ecoregion 11f is lower, drier, and less maritime-influenced than the Mesic Forest Zone (11l). Douglas-fir and ponderosa pine forests are common and contrast with the grassland of the lower, drier Ecoregion 11g.
11g. In the Canyons and Dissected Uplands ecoregion, the Snake and Salmon river systems have cut into the Columbia Plateau to depths of over 3,000 feet. Basalt and metamorphosed rocks are typically exposed in the canyon walls; the rock assemblage differs from the basalts of the Lower Snake and Clearwater Canyons (10l). The depth of the canyons and the exposed metamorphic rocks result in stony soils on canyon slopes that retain little moisture. Bluebunch wheatgrass and Sandberg’s bluegrass are adapted to grow under these hot, dry conditions. Land use includes grazing and recreation in the Hells Canyon National Recreation Area.
11i. The Continental Zone Foothills ecoregion lies between Oregon's Blue and Wallowa mountains and the northwestern Snake River Plain (12). The combined masses of the Cascade Range and the Blue and Wallowa mountains block any maritime influence, creating a continental climate. As a result, plants are subject to wide temperature ranges, high evapotranspiration, and high early-season moisture stress. The vegetation is characterized by a diverse bunchgrass and shrub community that varies according to soil depth, texture, and elevation. The shrublands provide valuable winter habitat for wildlife. Only a few perennial streams occur and originate in the surrounding mountain ranges.
11l. The Mesic Forest Zone is found between 6,000 and 7,400 feet in the western Seven Devils Mountains. It is influenced by maritime air coming through Oregon’s Columbia River Gorge. Precipitation mostly falls as snow that persists late into the spring. The soils typically retain moisture during the dry season because they often contain volcanic ash and are not rocky. As a result, forests are highly productive and diverse. Vegetation includes Douglas-fir, grand fir, ponderosa pine, subalpine fir, mountain big sagebrush, and mountain brush.
11m. The Subalpine–Alpine Zone includes the highest areas of the Seven Devils Mountains. It begins near tree line at an elevation of 6,500 feet, where the forest cover becomes broken by alpine meadows, and continues through alpine meadowland to include the exposed rock, snowfields, and glacial ice of the highest mountain peaks. Cold soils, deep snowpack, and a very short growing season are characteristic and support very open, non-commercial stands of subalpine fir, Engelmann spruce, and whitebark pine. Historically, green fescue and sedges covered the high alpine meadows, but, following intense grazing pressure by sheep early in the 20th century, many high elevation plant associations reverted to seral or exotic species.
|12. Snake River Plain|
The plains and low hills of Ecoregion 12 are part of the xeric intermontane west. Where irrigation water and soil depth are sufficient, sugar beets, potatoes, alfalfa, small grains, or vegetables are grown. Elsewhere, livestock grazing is widespread. Cattle feedlots and dairy operations are found locally. Potential natural vegetation is mostly sagebrush steppe but barren lava fields and saltbush–greasewood also occur. Streams generally have lower gradients, are warmer, and have finer grained substrates than do streams in the montane ecoregions. Streams typically have higher primary productivity than streams with a forest canopy overstory. Natural stream fish assemblages in Ecoregion 12 are typically a mix of mesothermal minnows and suckers but some stenothermal salmonids and sculpins are also present. Ecoregion 12j has many large springs along the Snake River that support endemic fish and mollusc species. Shoshone Falls is a major zoogeographic barrier and different species occur above and below it.
|12a. The Treasure Valley ecoregion has irrigated cropland, pastureland, and rapidly growing cities, suburbs, and industries. Many canals, reservoirs, and diversions occur. Aridic soils predominate and require irrigation to grow commercial crops. Surface water quality has been significantly affected by channel alteration, dams, irrigation return flow, and urban, industrial, and agricultural pollution. Crops include wheat, barley, alfalfa, sugar beets, potatoes, and beans. Crop diversity is greater, temperatures are warmer, and the mean frost free season is longer than in Ecoregions 12e and 12i. Population density is much greater than in nearby, rangeland-dominated ecoregions. |
12b. The Lava Fields ecoregion contains basalt flows, cinder cones, and spatter cones. Exposed basalt or very shallow loessial soils over volcanics are characteristic and are either barren or sparsely covered by hardy shrubs and grasses. Livestock carrying capacity is low. Surface water availability is very limited. Ecoregion 12b includes the Craters of the Moon National Monument and parts of the Idaho National Laboratory. Lithology, depth to bedrock, stock carrying capacity, and water availability are unlike neighboring ecoregions.
12c. The Camas Prairie ecoregion is a cold, wet valley used for small grain and alfalfa farming, pasture, range, and wildlife refuge. It is flanked by the foothills of Ecoregions 12f and 16f. These foothills trap mountain runoff in Ecoregion 12c. Resultant wet soils and flooding occur and are local and seasonal problems. Frigid Mollisols are common and are colder than the soils of the lower Treasure Valley (12a). Wet bottomlands support meadow grasses and sedges. Alluvial fans and terraces are covered by grasses and sagebrush.
12d. The Dissected Plateaus and Teton Basin ecoregion is used as cropland and rangeland. Potatoes are an important cash crop. Sprinkler-irrigated land supports potatoes, alfalfa, and pasture; surface irrigation is far less common than in Ecoregion 12e which is lower, flatter, and adjacent to the Snake River. Non-irrigated land grows small grains. Mollisols developed in thick loess deposits or alluvium and are subject to wind erosion. Loess is far more extensive than in Ecoregion 12e. Potential natural vegetation is sagebrush steppe and is unlike the forests of the higher, more rugged Ecoregion 17. Wet meadows occur in the poorly-drained, relatively cold Teton Basin.
12e. The nearly level Upper Snake River Plain contains cropland, pastureland, cities, suburbs, and industries. Extensive surface-irrigated small grain, sugar beet, potato, and alfalfa farming occurs. Frost-free season is shorter and crop variety is less than downstream in Ecoregions 12a and 12i. Ecoregion 12e is lower and less rugged than Ecoregions 12d and 80b. Aquatic resources have been degraded by irrigation diversions, channelization, dams, sewage treatment, nonpoint pollution, food processing, and phosphate processing.
12f. The shrub- and grass-covered Semiarid Foothills ecoregion is higher and more rugged than nearby Ecoregions 12a, 12c, and 12h. A few perennial streams flow across the ecoregion but are absent on the lacustrine deposits of the Unwooded Alkaline Foothills (12j). Shallow, clayey soils are common and often support medusahead wildrye, cheatgrass, and scattered shrubs. Wildfire frequency is high. Land use is primarily livestock grazing and is distinct from the irrigated agriculture of the Treasure Valley (12a).
12g. The Eastern Snake River Basalt Plains ecoregion typically has shallow, stony soils that are unsuitable for cultivation. Only small areas have soils deep enough to be farmed under sprinkler irrigation. Rangeland is widespread and contrasts with the cropland of Ecoregions 12d, 12e, and 12i. Potential natural vegetation is mostly sagebrush and bunchgrass. It is cool enough to have some regeneration capacity and still contains native plants unlike Ecoregion 12h. Eastern parts of Ecoregion 12g are higher and more continental than the west.
12h. The Mountain Home Uplands ecoregion is arid and shrub- and grass-covered. It is mostly rangeland and is sparsely populated unlike Ecoregions 12a and 12i. Local relief is between that of the flanking foothills and the Magic and Treasure valleys. Mesic soils are common and are warmer than the frigid soils of Ecoregion 80a. Today, cheatgrass, medusahead wildrye, and sagebrush occur and stock carrying capacity is low; native grasses are much rarer and vegetative regeneration capacity is more limited than in the cooler Ecoregion 12g.
12i. The Magic Valley ecoregion is underlain by alluvium, loess, and basalt flows. Its aridic soils require irrigation to grow commercial crops. Many canals, reservoirs, and diversions supply water to its pastureland, cropland, and residential, commercial, and industrial developments. Small grains, alfalfa, sugar beets, potatoes, and beans are grown. Livestock and dairy farms occur; dairying is more common than in Ecoregion 12a. Dams, irrigation diversions, pollution, and channel alteration have affected water quality. Over-watering from sprinkler-irrigated portions of Ecoregion 12g has raised groundwater levels and created artificial wetlands. Natural vegetation is mostly sagebrush and bunchgrass but low terraces have salt tolerant plants. Population density is greater than in the rangeland-dominated Ecoregions 12g and 12h.
12j. The shrub- and grass-covered Unwooded Alkaline Foothills ecoregion is higher and more rugged than Ecoregion 12a. Sandy, alkaline lacustrine deposits occur unlike in other ecoregions and support a unique flora. Potential natural vegetation is saltbush–greasewood and sagebrush steppe. Today, cheatgrass and crested wheatgrass are also common and the ecoregion is used for livestock grazing. Land use is unlike that of Ecoregions 12a and 12i. Perennial streams are rare and are much less common than in Ecoregion 12f.
|13. Central Basin and Range |
Ecoregion 13 is internally-drained and composed of north-trending, fault-block ranges and intervening, drier basins. It is vast and includes parts of Nevada, Utah, California, and Idaho. In Idaho, sagebrush grassland, saltbush–greasewood, mountain brush, and woodland occur; forests are absent unlike in the cooler, wetter, more rugged Ecoregion 19. Grazing is widespread. Cropland is less common than in Ecoregions 12 and 80.
|13b. The arid Shadscale-Dominated Saline Basins ecoregion is nearly flat, internally-drained, and has light-colored alkaline soils that are dry for long periods. Its salt- and drought-tolerant shadscale and greasewood are unlike the Wyoming big sagebrush and bluebunch wheatgrass of the less saline Ecoregion 13c. Ecoregion 13b is mostly rangeland. Irrigated farming is rarer than in Ecoregions 13i and 80h. |
13c. The semiarid Sagebrush Basins and Slopes ecoregion is not as saline, dry, or level as Ecoregions 13b or 80h and is not as rocky, rugged, or wooded as Ecoregion 80b. It is internally drained in contrast to Ecoregions 80a and 80i which drain to the Snake River. Livestock grazing is the primary land use.
13d. The Woodland- and Shrub-Covered Low Mountains ecoregion is higher, wetter, rockier, and more rugged than nearby grass- and shrub-covered ecoregions. Shallow soils support mountain big sagebrush, mountain brush, Utah juniper, and grasses.
13i. The Malad and Cache Valleys ecoregion is wetter, more widely farmed, and more populated than Ecoregion 13c. Mountain-fed perennial streams and canals supply water to pastureland, towns, and cropland growing hay and small grains. It is internally-drained and was inundated by Lake Bonneville unlike Ecoregion 80i. The Cache Valley has a shorter growing season than the Malad Valley.
|15. Northern Rockies|
Ecoregion 15 is mountainous and rugged. Climate, trees, and understory species are characteristically maritime-influenced. Douglas-fir, subalpine fir, Englemann spruce, western larch, lodgepole pine, and ponderosa pine as well as Pacific indicators such as western redcedar, western hemlock, mountain hemlock, and grand fir occur. Pacific tree species are more numerous than in the Idaho Batholith (16) and are never dominant in the Middle Rockies (17). Western white pine was once common but has been decimated by blister rust, early to mid-20th century logging, and fire suppression. Whitebark pine is also undergoing a massive population decline due to the effects of white pine blister rust, mountain pine beetle, and fire. Ecoregion 15 is not as high nor as extensively snow- and ice-covered as the Canadian Rockies (41). Granitic rocks and associated management problems are less extensive than in the Idaho Batholith (16). Thick volcanic ash deposits are more widespread than in Ecoregion 16. Logging and mining are common and have caused stream water quality problems in the region. Natural stream fish assemblages have low diversity and seldom have more than four native species present. Streams have a nearly universal cold-water adapted fish assemblage of salmonids, sculpin, sucker and dace. Salmon, steelhead, and lamprey formerly occurred in Ecoregion 15i prior to dam construction.
|15f. The Grassy Potlatch Ridges ecoregion is underlain by volcanics and mantled by loess and volcanic ash. Idaho fescue, bluebunch wheatgrass, bluegrass, snowberry, and, on cooler, moister sites, scattered ponderosa pine occur and contrast with the forests of Ecoregion 15v and the forests and savannas of Ecoregion 15j. Today, small grain farming, hay operations, and livestock grazing are extensive. |
15h. The High Northern Rockies ecoregion traps large amounts of Pacific moisture and is characterized by mixed high [[[elevation]] vegetation, rock outcrops, deep winter snow pack, a short growing season, tarns, and talus. Soils are very stony but often contain volcanic ash. Above treeline, tundra, alpine grassland, meadows, and wetlands occur. Subalpine fir, lodgepole pine, whitebark pine, mountain hemlock, and alpine larch grow in rocky glacial cirques or on exposed sites as scattered trees, very open-canopied parklands, or krummholz.
15i. The Clearwater Mountains and Breaks ecoregion is exposed to substantial maritime influence, mantled by thick volcanic ash, and underlain by granitics. It is lithologically unlike Ecoregions 15o and 15p and higher than Ecoregions 15n and 15v. Its moist coniferous forests lack western hemlock and are transitional between those of the Idaho Panhandle and the drier forests of the southern Idaho Batholith.
15j. The deep, narrow Lower Clearwater Canyons are lower, drier, warmer, and have been more developed than Ecoregion 16c or the physiographically distinct hills and mountains of Ecoregions 15i, 15n, 15p, and 15v. Savanna, Douglas-fir–ponderosa pine forest, and, in riparian areas, western redcedar–western white pine–grand fir forest occur. Forests are more widespread on canyon bottoms than on slopes.
15m. The broad, glacial-scoured Kootenai Valley is drier than the valleys of Ecoregion 15u because it lies in the rain shadow of the Selkirk Range. Tree species diversity is high; representatives of both moist and dry gradients occur. The Kootenai River winds across a wide flood plain that has been reclaimed with levees and intensively farmed. Logging is common in the east near the mountainous Ecoregion 15q.
15n. The Weippe Prairie ecoregion is a gently sloping basalt plateau that is mantled by loess and volcanic ash. It is lithologically unlike Ecoregions 15i and 15p. Maximum elevations are lower than in the more rugged Ecoregions 15i, 15p, and 15v. Its mixed coniferous forest contains ponderosa pine, Douglas-fir, grand fir, western redcedar, and western larch. Hay farming, grazing, and logging are common.
15o. The Coeur d’Alene Metasedimentary Zone is forested and underlain by fractured quartzite and argillaceous rock. It is more rugged than Ecoregions 15s, 15u, and 15v and lithologically unlike Ecoregions 15i and 15p. Slope instability and channel sedimentation is usually less than in Ecoregions 15p or 15y but fault crush zones are notably unstable. Douglas-fir, grand fir, western redcedar, western hemlock, and, at higher elevations, mountain hemlock, subalpine fir, Engelmann spruce, and whitebark pine occur. Smelter emissions have denuded some slopes. Acid drainage from mine tailings have left some streams nearly devoid of aquatic life. Massive restoration efforts are now underway.
15p. The St. Joe Schist–Gneiss Zone is mountainous, mantled by volcanic ash, and prone to landslides. Rocks are more weathered and slopes are more unstable than in Ecoregion 15o. High gradient streams dissect the region and receive episodic sedimentation from slides. Streams were used to transport logs to mills; log drives greatly altered aquatic ecosystems and stream morphology. Pacific influence is greater than to the south. Potential natural vegetation is mapped as cedar–hemlock–pine but hemlock is absent in the south. Near treeline, mountain hemlock, subalpine fir, Engelmann spruce, and whitebark pine occur.
15q. The Purcell–Cabinet–North Bitterroot Mountains ecoregion is mantled by volcanic ash and glacial deposits and is underlain by quartzite and argillaceous rocks. Continental ice shaped its terrain but did not extend further south. Potential for natural and management-induced slope instability exists where water tables are perched in compacted tills and glacio-fluvial deposits. However, in general, slopes yield less sediment to streams after disturbance than in nearby granitic and schistic areas. Cedar–hemlock–pine forest and, at higher elevations, western spruce–fir forest occur. Birch and aspen grow on floodplains and are seral species on moist, low to mid-elevation uplands.
15s. The Spokane Valley Outwash Plains ecoregion is gently rolling and includes the southern end of the Purcell Trench and the Spokane Valley. It once served as the main outlet for the Pleistocene Missoula Floods. In the northern valleys, coarse, gravelly soils developed from glacial outwash. In the southern Spokane Valley, more arable soils occur and developed from glacial lake sediment. Dry, open ponderosa pine and Douglas-fir woodlands occur and are distinct from the moist, maritime-influenced forests of Ecoregions 15o and 15u.
15u. The Inland Maritime Foothills and Valleys ecoregion includes the wide, glaciated Pend Oreille and Priest valleys. Soils have more volcanic ash and water holding capacity than the drier Columbia, Kettle, and Sanpoil valleys of northeast Washington. Forests contain western hemlock, western redcedar, grand fir, Douglas fir, ponderosa pine, lodgepole pine, and an unusually large proportion of western larch. Birch and aspen grow on floodplains and are also common seral species on moist, low to mid-elevation uplands. These upland hardwoods may reflect boreal influence; they also occur in Ecoregion 15q but are not widespread elsewhere in the Northern Rockies (15) of Idaho.
15v. The Northern Idaho Hills and Low Relief Mountains ecoregion is not as rugged nor as high as Ecoregions 15o and 15p. It is mantled by volcanic ash and loess and has rich, forest-type soils that are unlike the grassland-type soils of Ecoregion 10. Grand fir, western redcedar, Douglas fir, and ponderosa pine are common. Western hemlock is less widespread than in Ecoregions 15o and 15p, never abundant, and absent from the south. Its productive forests are widely logged; logging is easier and cheaper than in more rugged terrain.
15w. The mountainous Western Selkirk Maritime Forest ecoregion is more rugged than Ecoregion 15v. Douglas-fir dominates or codominates most overstories. Maritime species such as grand fir, western redcedar, and western hemlock are more common than in the rain shadow of the North Cascades in Washington’s Okanogan Highland. Boreal influence is absent in contrast to northern Ecoregion 15y.
15y. The dissected, partly glaciated Selkirk Mountains ecoregion is rugged, covered in mixed coniferous forest, and mantled by volcanic ash that increases forest productivity. Both Pacific species (grand fir, western redcedar, and western hemlock) and Rocky Mountain species (western larch, western white pine, and lodgepole pine) are common. Ecoregion 15y is wetter and has more maritime influence than Ecoregion 15w. A combination of weather patterns, high relief, and very narrow valleys result in more summer precipitation, fog, and relative humidity at low and mid-elevations than elsewhere in northern Idaho. Boreal influence is stronger, subalpine fir–spruceforests are lower, and whitebark pine forests are more extensive than in the rest of the Northern Rockies (15). Boreal influence increases toward the north and some north-facing valleys have extensive peatlands. Ecoregion 15y includes the largest contiguous old growth cedar–hemlock forest in the interior U.S., extensive peatlands, and important lynx and grizzly bear habitat. It supports the only woodland caribou herd in the conterminous U.S. Erosion hazards can be high where road beds intercept perched water tables above subsurface compacted tills. Avalanche chutes are common.
|16. Idaho Batholith |
Ecoregion 16 is mountainous, deeply dissected, partially glaciated, and characteristically underlain by granitic rocks. The lithological mosaic and related slope stability and water quality issues are different from Ecoregions 15 and 17. Soils derived from granitics are droughty and have limited fertility, and therefore provide only limited amounts of nutrients to aquatic ecosystems. They are highly erodible when vegetation is removed. Maritime influence is slight and lessens toward the south. Grand fir, Douglas-fir, western larch, and, at higher elevations, Engelmann spruce and subalpine fir occur; ponderosa pine, shrubs, and grasses grow in deep canyons. Pacific tree species are less numerous than in Ecoregion 15; western hemlock is absent and western redcedar is limited to the north. Overall, the vegetation is unlike that of Ecoregions 15 and 17. Land uses include logging, grazing, and recreation. Streams are likely to suffer from increased loads of fine sediments after disturbance by humans. Declining anadromous fish runs once brought much needed nutrients but are now in danger of extirpation due to dams on the Columbia and lower Snake rivers, hatchery operations, and habitat degradation. Fish assemblage composition is similar to Ecoregion 15. Macroinvertebrate assemblages are more similar to those found in Ecoregions 12, 17, and 80 than to those found in Ecoregion 15.
|16b. The mountainous Lochsa Uplands ecoregion is dissected but not as deeply as Ecoregion 16c. It is mostly underlain by granitic rocks and mantled by volcanic ash deposits that increase the fertility and water retention of upland soils. Grand fir, Douglas-fir, and western larch are common, Engelmann spruce and subalpine fir grow at high elevations, and redcedar occurs on north-facing slopes and in canyons. Maritime influence is less than to the north but greater than to the south. Logging and road building cause landslides and stream sedimentation. |
16c. The deeply dissected Lochsa–Selway–Clearwater Canyons ecoregion contains cold, fast-flowing rivers. Local relief is greater than in the nearby mountains. Canyons become warmer and drier with increasing depth. Ecoregion 16c is dominated by Douglas-fir, grand fir, western redcedar, western larch, and western white pine. Ponderosa pine grows on lower, drier sites. The forest canopy is more closed than in the warmer and drier Ecoregion 16j. Extensive wilderness occurs and includes the Selway River watershed. Elsewhere, logging is common.
16d. The Dry, Partly Wooded Mountains ecoregion is largely underlain by sedimentary and extrusive rocks; granitics are less common than in other parts of the Idaho Batholith (16). Ecoregion 16d is in the rain shadow of high mountains. Winter precipitation is less than in Ecoregions 16h and 16k and maritime influence is absent. A mosaic of shrubland, open Douglas-fir forest, and aspen occurs and is unlike other parts of Ecoregion 16. Mining has affected water quality. Rapid residential and commercial growth is occurring near Ketchum.
16e. The Glaciated Bitterroot Mountains and Canyons ecoregion is underlain by granitic rocks and mantled by volcanic ash and glacial till. Peaks, lakes, wetlands, and deep glaciated valleys occur. Landforms and lithology are different from nearby ecoregions. Summits are high enough to trap Pacific moisture. Grand fir, Douglas-fir, and western larch are common and Engelmann spruce and subalpine fir occur at high elevations and on north-facing slopes. Ecoregion 16e is mostly roadless or designated wilderness and recreation is an important land use.
16f. The Foothill Shrublands–Grasslands ecoregion is in the rain shadow of high mountains. Its hills and benches are dry, treeless, and covered by shrubs and grasses. The vegetation mosaic is unlike the open forests of Ecoregion 16k and the mountain sagebrush/forest mosaic of the lithologically distinct Ecoregion 16d. Land use is mostly grazing but rural residential development is expanding near Boise.
16g. The High Glacial Drift-Filled Valleys ecoregion contains terraces, outwash plains, moraines, wetlands, and hills that are much less rugged and less forested than Ecoregion 16k. Originally, sedges and rushes were common on wet soils, bunchgrasses and mountain big sagebrush occurred on drier soils, and lodgepole pine and ponderosa pine grew on valley floors. Winters are cold and snowy. Ecoregion 16g receives large amounts of spring runoff from mountain snow pack. It is summer pasture for large numbers of livestock; cropland and growing residential and recreational developments also occur. Flood irrigation and grazing have raised sediment and phosphorus levels in streams.
16h. The wet, severely exposed, glaciated High Idaho Batholith contains jagged peaks, tarns, and rockland. It is often snowcapped and annual precipitation is greater than in nearby, lower ecoregions. Soils are very stony and have a cryic temperature regime. Above treeline, tundra, alpine grassland, meadows, and wetlands occur. Subalpine fir, lodgepole pine, whitebark pine, mountain hemlock, and alpine larch grow in rocky glacial cirques or on exposed sites as scattered trees, very open-canopied parklands, or krummholz.
16i. The South Clearwater Forested Mountains ecoregion receives more maritime influence than ecoregions to the south but less than those to the north. Grand fir is usually the sole maritime tree species in the elevational zone between Douglas-fir and subalpine fir. Logging has caused slope instability (especially in granitic areas) and stream sedimentation. Placer gold mining has also heavily affected rivers.
16j. The Hot Dry Canyons ecoregion is deeply dissected. Local relief can approach 5,000 feet and canyons become warmer and drier with increasing depth. Overall, it is warmer and drier than Ecoregions 16i and 16k. There is little winter snowfall. Ponderosa pine, mountain sagebrush, and grasses are widespread; Douglas-fir also occurs but is less common than in Ecoregion 16c. South-facing slopes are drier and less wooded than north-facing slopes. Mining has affected canyon bottoms some of which now serve as transportation corridors.
16k. The Southern Forested Mountains ecoregion is mantled by droughty soils derived from granitic rocks and is only marginally affected by maritime influence. Forest diversity is less than in wetter Ecoregion 16b. Open Douglas-fir is common, grand fir and subalpine fir occur at higher elevations, and ponderosa pine grows in canyons. Mountain sagebrush and forest are found in the south. Streams are subject to high sediment loading when soils are disturbed. Macroinvertebrate assemblages are distinct from those of Ecoregion 16i.
|17. Middle Rockies |
The climate of Ecoregion 17 lacks the strong maritime influence of Ecoregion 15. Mountains have Douglas-fir, subalpine fir, and Engelmann spruce forests and alpine areas; Pacific tree species are never dominant and forests can have open canopies. Foothills are partly wooded or shrub- and grass-covered. Intermontane valleys are grass- and/or shrub-covered and contain a mosaic of terrestrial and aquatic fauna that is distinct from nearby mountains. Many mountain-fed streams occur. Granitics and associated management problems are less extensive than in Ecoregion 16. Recreation, logging, mining, and summer livestock grazing are common land uses. Stream fish assemblages are similar to those found in Ecoregions 15 and 16 and are dominated by salmonids and cottids. The Lost Streams of Idaho constitute an unique set of isolated lotic environments that are separated from other systems by the Eastern Snake River Basalt Plains (12g). Fish populations may also be seasonally isolated by the intermontane valleys of Ecoregion 17aa. The Pahsimeroi and Lemhi rivers are important chinook salmon spawning streams.
|17e. The Barren Mountains ecoregion is largely underlain by quartzite and carbonate-rich rocks and is drier than mountainous ecoregions to the north. Elevations are higher than those of Ecoregion 17ab and range from about 6,800 to 10,000 feet. Open-canopied Douglasfir– lodgepole pine–subalpine fir forests, aspen groves, sagebrush, mountain brush, and grasses occur. Forests are limited to a narrow elevational band and are most widespread on north-facing slopes. Pacific forest elements are absent and barrens are common. |
17h. The wet, severely exposed, glaciated High Elevation Rockland Alpine Zone contains jagged peaks, tarns, rockland, and talus deposits. It is often snowcapped and maximum annual precipitation is greater than in surrounding, but lower, ecoregions. Soils are stony and have a cryic temperature regime. Alpine tundra, alpine grassland, subirrigated meadows, and wetlands occur above timberline. Krummholz vegetation occupies windswept areas near timberline. Subalpine fir and whitebark pine are found in glacial cirques.
17j. The West Yellowstone Plateau ecoregion contains rhyolite and basalt flows, lakes, springs, outwash plains, moraines, canyons, and wetlands. Its terrain is generally subdued in contrast to the more mountainous portions of Ecoregion 17 but scattered ridges and buttes occur. Ecoregion 17j has a coniferous forest–shrubland mosaic. Forests dominated by Douglas-fir, lodgepole pine, and aspen are most common on north-facing slopes and flatter uplands. Recreation is a very important land use but mining, grazing, and logging also occur.
17l. The rugged Gneissic–Schistose Forested Mountains ecoregion is glaciated, wet, and lithologically unlike nearby ecoregions. Its streams have flashy hydrographs; they experience only a short delay between rainfall and runoff peaks and have low flows during drought and freezing periods. Douglas-fir, lodgepole pine, and subalpine fir are common. Land uses include recreation, logging, and grazing.
17n. The Cold Valleys contain bottomlands, terraces, marshlands, alluvial fans, and foothills that are nestled below the Partly Forested Mountains (17o). Mean annual frost-free season is brief, 40 to 90 days, and shorter than in the Sagebrush Steppe Valleys (80i). Potential natural vegetation is mostly sagebrush steppe. Wet bottomlands support sedges, rushes, and willows. Pastureland, rangeland, and small grain, alfalfa, and potato farming occur. Fields, streams, and marshes are important habitat for both nesting and migratory birds.
17o. The steep, dry Partly Forested Mountains vary in elevation from about 6,000 to over 9,000 feet. Soils have a cryic temperature regime and are rocky and shallow. They support open-canopied forests, shrublands, and grasslands; Douglas-fir, lodgepole pine, and aspen are most common on north-facing slopes and gently sloping uplands while mountain big sagebrush and mountain brush dominate southfacing slopes. Its vegetation is distinct from surrounding ecoregions. Ecoregion 17o is used as summer range and for timber production.
17aa. The Dry Intermontane Sagebrush Valleys ecoregion contains stream terraces, floodplains, saline areas, and alluvial fans. Water availability and potential for cropland agriculture are low because Ecoregion 17aa is in the rain shadow of high mountains, receives little mountain runoff, and is underlain by highly permeable valley fill deposits. Its deep gravels are unlike the basalts of Ecoregion 12. Sagebrush grassland is widespread and contrasts with the open-canopied forests of the more rugged and higher Ecoregion 17e. Shadscale and greasewood grow on alkaline soils that receive less than 8 inches of precipitation annually. Grazing is the dominant land use. Both the Pahsimeroi and Lemhi rivers were once important salmon and steelhead fisheries.
17ab. The semiarid Dry Gneissic–Schistose–Volcanic Hills ecoregion is shrub- and grass-covered and is underlain by Quaternary and Tertiary volcanics. It is less rugged and drier than the higher Barren Mountains (17e) but is more rugged and receives more precipitation than the lower Dry Intermontane Sagebrush Valleys (17aa). Its sagebrush-grassland vegetation contrasts with the open-canopied forest–shrubland–grassland mosaic of Ecoregion 17e. Grazing is the most common land use in Ecoregion 17ab.
17ad. The Western Beaverhead Mountains ecoregion occupies the elevational band between the High Elevation Rockland Alpine Zone (17h) and the lower, less rugged Ecoregion 17ab. It is underlain by quartzite and argillite; the lithologic mosaic and related slope stability and water quality issues are unlike those of Ecoregion 16k. Vegetation is affected by elevation and slope aspect. Mountain big sagebrush, mountain brush, and understory grasses grow on south-facing slopes and Douglas-fir, lodgepole pine, aspen, and subalpine fir occur on north-facing slopes. Land uses include grazing, mining, recreation, and logging.
|18. Wyoming Basin |
Ecoregion 18 is a broad intermontane basin containing rolling plains, high hills, and mesas. It is most extensive in Wyoming but also extends into other states including Idaho. Ecoregion 18 is dominated by arid grasslands sand shrublands and lacks the extensive forests of neighboring, mountainous Ecoregions 17 and 19. Land use is primarily livestock grazing but irrigated hayland also occurs.
|18c. The Wet Valleys ecoregion is characterized by wetlands, lakes, canals, cold winters, and a short growing season. Nearly flat, poorly drained floodplains and low terraces are widespread and support sedges, rushes, cattails, marsh grasses, annual bluegrass, and clover. Well-drained alluvial fans and foothills covered in sagebrush grassland act as a transition to the surrounding and much more rugged Partly Forested Mountains (17o), Semiarid Bear Hills (18d), and Semiarid Foothills (19f). Mollisols occur and have a frigid temperature regime. Land use is irrigated hayland, meadow pastureland, and rangeland. Land use and drainage conditions are all different from neighboring ecoregions.|
18d. The Semiarid Bear Hills ecoregion is located in the rain shadow of high mountains. Its terrain is hilly and is distinct from the nearly flat Wet Valleys (18c) and the much more rugged Wasatch and Uinta Mountains (19). Bunchgrasses and mountain big sagebrush occur and contrast with the forests of nearby, mountainous ecoregions. Land use is primarily grazing and is unlike the mosaic of irrigated hayland, meadow pastureland, and rangeland of Ecoregion 18c.
| 19. Wasatch and Uinta Mountains |
Ecoregion 19 contains a core area of high, precipitous mountains with narrow crests and valleys. At middle elevations, Douglas-fir and aspen parkland are common. At highest elevations and on steep, north-facing slopes, Engelmann spruce and subalpine fir occur. Semiarid foothills support widely spaced juniper in a matrix of sagebrush grassland. Perennial streams provide water to lower, more arid regions. Summer livestock grazing is an important land use and is more common than in Ecoregion 17. Bear Lake supports three endemic species of fish.
| 19d. The Wasatch Montane Zone is found above about 7,400 feet elevation. Its mountains are covered in a mixture of mountain big sagebrush, mountain brush, and conifer forests. Douglas-fir and aspen parkland are common on north-facing slopes and many less sloping areas. Mountain big sagebrush, snowberry, and understory grasses grow on south-facing slopes. Engelmann spruce and subalpine fir grow at highest elevations and on steep, north-facing slopes. The vegetation mosaic is unlike the sagebrush grassland and widely spaced junipers of the lower Semiarid Foothills (19f). |
19f. The Semiarid Foothills ecoregion ranges in elevation from about 5,500 to 8,200 feet. Widely spaced junipers occur in a matrix dominated by mountain big sagebrush and bluebunch wheatgrass. Overall, the vegetation is distinct from that of the higher, wetter Wasatch Montane Zone (19d). Livestock grazing is common. Some rangeland has been cleared of trees and reseeded to grasses.
| 80. Northern Basin and Range |
Ecoregion 80 consists of dissected lava plains, rolling hills, alluvial fans, valleys, and scattered mountains. It is higher and cooler than Ecoregion 12 and has more available moisture than Ecoregion 13. Basins support sagebrush grassland or saltbush greasewood vegetation; cool season grasses and Mollisols are more common in the basins of Ecoregion 80 than in the hotter and drier basins of Ecoregion 13 where Aridisols support sagebrush, shadscale, and greasewood. Ranges are covered in mountain sagebrush, mountain brush, Idaho fescue, Douglas-fir, or aspen. Juniper woodlands occur on rugged, stony uplands. Both rangeland and cropland occurs. Ecoregion 80 lies between Ecoregion 13 to the south and Ecoregions 11 and 12 to the north; its southern boundary is the highest shoreline of Pleistocene Lake Bonneville which once inundated much of Ecoregion 13 but not Ecoregion 80. Stream fish communities share features of Ecoregions 12 and 17. In the Owyhee Mountains, Ecoregions 80j and 80k, isolated by the surrounding lower, warmer regions, once supported anadromous fish.
| 80a. The Dissected High Lava Plateau ecoregion has alluvial fans, rolling plains, and shear-walled canyons that are cut into extrusive rocks. Sagebrush grassland is common and scattered woodland grows on rocky uplands. Overall, Ecoregion 80a is less wooded, lower, and more arid than Ecoregions 80b, 80c, 80j, or 80k. Ecoregion 80a has more cool season grasses than Ecoregion 13c and lacks the saltbush–greasewood of Ecoregion 80h. Frigid and mesic Aridisols and Mollisols occur. Grazing is the primary land use. Cropland is much less common than in Ecoregions 12a and 12i. Areas of high water quality and native fish assemblages occur in isolated canyons. |
80b. The Semiarid Hills and Low Mountains ecoregion occupies the elevational band between Ecoregion 80c and the lower, less rugged Ecoregions 12e, 80a, and 80i. Potential natural vegetation is mostly sagebrush steppe. Cool season grasses are more common than in the drier Ecoregion 13c which has less available moisture and has a potential natural vegetation of Great Basin sagebrush. Forest components are much less common than in Ecoregion 80c. Juniper woodland grows on rock outcrops but is not as common as in Ecoregion 13d. Land use is primarily livestock grazing.
80c. The High Elevation Forests and Shrublands ecoregion is mountainous and occupies the elevational band above Ecoregion 80b. It is characterized by a mix of conifers, mountain brush, and sagebrush grassland. North-facing slopes and many flatter areas support open stands of Douglas-fir, aspen and lodgepole pine; overall, forest components are more common than in Ecoregions 80a and 80b which are dominated by sagebrush grassland or juniper woodland. Winters are colder and mean annual precipitation is greater than in lower ecoregions.
80e. The High Desert Wetlands ecoregion is critical habitat for nesting and migratory birds. Sedges, meadow barley, creeping wildrye, and Nevada bluegrass are found in wetter areas. Water levels in its lakes and wetlands fluctuate seasonally and annually.
80f. The Owyhee Uplands and Canyons ecoregion contains deep, precipitous river canyons, barren lava fields, badlands, and tuffaceous outcrops that are riddled by caves. Lithology is more varied, stream density is higher, and water availability is greater than in Ecoregion 80a. Ecoregion 80f is important wildlife habitat. Sagebrush grassland occurs; it is unlike the saltbush–greasewood of Ecoregion 12j.
80h. The Saltbush-Dominated Valleys ecoregion is arid, gently sloping, and dominated by shadscale and greasewood. Light-colored soils with high salt and alkali content are common; they are dry for extended periods and may be leached of salt by irrigation water. Potential natural vegetation is saltbush–greasewood; it is distinct from that of surrounding ecoregions. The primary land use is grazing but irrigated cropland occurs and is much more common than in Ecoregion 13b. Ecoregion 80h drains to the Snake River and was not flooded by Pleistocene Lake Bonneville in contrast to Ecoregion 13b.
80i. The Sagebrush Steppe Valleys ecoregion is flanked by the hills and mountains of Ecoregions 80b and 80c. It is dominated by sagebrush grassland and lacks the woodland of Ecoregion 80b, the open conifer forest of Ecoregion 80c, and the saltbush–greasewood of Ecoregions 13b and 80h. Perennial bunchgrasses are more abundant than in the Sagebrush Basins and Slopes (13c) in Utah. Valleys mostly drain to the Snake River and fish assemblages are unlike those of the internally-drained basins to the south in Ecoregion 13. Grazing is the dominant land use but non-irrigated wheat and barley farming is much more common than in the semiarid basins of Ecoregion 13. The Sagebrush Steppe Valleys (80i) ecoregion is less suitable for cropland agriculture and has less available water than many parts of the Snake River Plain (12).
80j. The disjunct Semiarid Uplands ecoregion includes mid-elevation zones in the Owyhee and Jarbidge mountains and hills, volcanic cones, buttes, and rocky outcrops that rise out of neighboring, drier lava plains. Mountain sagebrush, western juniper, mountain brush, and grasses grow in the ecoregion. In the Jarbidge Mountains, juniper woodland can be of limited extent or entirely absent. Elsewhere, density and extent of juniper woodland varies with long term climate changes, grazing pressure, and fire suppression.
80k. The Partly Forested Mountains ecoregion occupies the elevational belt above the Semiarid Uplands (80j). Elevations exceed 6,500 feet. Annual precipitation is sufficient to support Douglas-fir, ponderosa pine, mountain big sagebrush, and mountain brush. The vegetation mosaic is unlike the western juniper woodland and sagebrush steppe of Ecoregion 80j.
- The full, original version of this entry is located here: http://www.epa.gov/wed/pages/ecoregions/id_eco.htm. That description contains additional maps, as well as information on the physiography, geology, soil, potential natural vegetation, and the land use and land cover of the ecoregion.
- PRINCIPAL AUTHORS: Chad L. McGrath (NRCS), Alan J. Woods (Dynamac Corporation), James M. Omernik (USEPA), Sandra A. Bryce (Dynamac Corporation), Mike Edmondson (IDEQ), John A. Nesser (USFS), James Shelden (USFS), Rex C. Crawford (Washington Department of Natural Resources), Jeffrey A. Comstock (Indus Corporation), and Milton D. Plocher (Dynamac Corporation).
- COLLABORATORS AND CONTRIBUTORS: Erwin Cowley (BLM), Carl Davis (USFS), Don A. Essig (IDEQ), Jerry Freeouf (USFS), Pat Green (USFS), Glenn Griffith (NRCS), Jimmy Kagan (Oregon Natural Heritage Program), Scott Lambert (Washington State University), Duane A. Lammers (USFS), John Lott (USFS), Thomas R. Loveland (USGS), Terry Maret (USGS), Michael McIntyre (IDEQ), Christopher Mebane (IDEQ), Neil Peterson (NRCS), Thor D. Thorson (NRCS), and Bill Ypsilantis (BLM).
- REVIEWERS: Arthur C. Zack (USFS, Idaho Panhandle National Forest), Gerald J. Niehoff (USFS, Idaho Panhandle National Forest), and Thomas M. Rice (USFS, Rocky Mountain Research Station).
- This project was partially supported by funds from the USEPA-Office of Research and Development's Environmental Monitoring and Assessment Program through contract 68-C6-005 to Dynamac Corporation.
- Bailey, R.G., Avers, P.E., King, T., and McNab, W.H., eds., 1994, Ecoregions and subregions of the United States (map) (supplementary table of map unit descriptions compiled and edited by McNab, W.H. and Bailey, R.G.): Washington, D.C., USFS, scale 1:7,500,000.
- Bryce, S.A., Omernik, J.M., and Larsen, D.P., 1999, Ecoregions – a geographic framework to guide risk characterization and ecosystem management: Environmental Practice, v. 1, no. 3, p. 141-155.
- Commission for Environmental Cooperation Working Group, 1997, Ecological regions of North America – toward a common perspective: Montreal, Commission for Environmental Cooperation, 71 p.
- Gallant, A.L., Whittier, T.R., Larsen, D.P., Omernik, J.M., and Hughes, R.M., 1989, Regionalization as a tool for managing environmental resources: Corvallis, Oregon, U.S. Environmental Protection Agency, EPA/600/3-89/060, 152 p.
- Griffith, G.E., Omernik, J.M., Wilton, T.F., and Pierson, S.M., 1994, Ecoregions and subregions of Iowa – a framework for water quality assessment and management: Journal of the Iowa Academy of Science, v. 101, no. 1, p. 5-13.
- Omernik, J.M., 1987, Ecoregions of the conterminous United States (map supplement): Annals of the Association of American Geographers, v. 77, no. 1, p. 118-125, scale 1:7,500,000.
- Omernik, J.M., 1995, Ecoregions – a framework for environmental management, in Davis, W.S. and Simon, T.P., eds., Biological assessment and criteria-tools for water resource planning and decision making: Boca Raton, Florida, Lewis Publishers, p. 49-62. ISBN: 0873718941.
- Omernik, J.M., Chapman, S.S., Lillie, R.A., and Dumke, R.T., 2000, Ecoregions of Wisconsin: Transactions of the Wisconsin Academy of Sciences, Arts, and Letters, v. 88, p. 77-103.
- U.S. Department of Agriculture–Soil Conservation Service, 1981, Land resource regions and major land resource areas of the United States: Agriculture Handbook 296, 156 p.
- U.S. Environmental Protection Agency, 2000, Level III ecoregions of the continental United States (revision of Omernik, 1987): Corvallis, Oregon, USEPA – National Health and Environmental Effects Research Laboratory, Map M-1, various scales.
- Wiken, E., 1986, Terrestrial ecozones of Canada: Ottawa, Environment Canada, Ecological Land Classification Series no. 19, 26 p.ISBN: 0662147618.
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