The assessment area includes three ecoregions in arctic Alaska: Beaufort Coastal Plain, Brooks Foothills, and Brooks Range. Included in these ecoregions are numerous braided river systems and 7 primary communities. The Dalton Highway traverses the region north-south to Prudhoe Bay, but does not provide road access to the primary communities. The assessment boundary constitutes the Beaufort Coastal Plain and the Brooks Foothills as well as the portion of the Brooks Range that lies to the north of the crest of the range. The descriptions below are paraphrased from Unified Ecoregions of Alaska (Nowacki et al. 2001).
Beaufort Coastal Plain
The Beaufort Coastal Plain is a treeless, wind-swept, flat to undulating plain that gradually ascends from the Beaufort Sea Coast south to the foothills of the Brooks Range. The ecoregion is underlain by unconsolidated marine, fluvial, glaciofluvial, and eolian deposits and lacks bedrock. A dry, polar climate dominates throughout the year. Winters are long and cold while summers are short and cool. Annual precipitation is low and falls mostly as snow during the winter. Permafrost is continuous across the region. Frost processes create the surface features that dominate the plain. Soils are generally saturated and have thick organic horizons. Because of the abundant thaw lakes and saturated soil, most of the region supports wetland communities. Dominant vegetation classes include wet sedge tundra, tussock tundra, and sedge-Dryas tundra. Low willow thickets grow on well-drained river banks. Anadramous arctic cisco, broad whitefish, least cisco, and Dolly Varden char overwinter in large braided rivers. The coastal plain supports large caribou herds and is an important calving area. Herbivores include muskox, lemmings, and arctic ground squirrels. Predators include arctic foxes, gray wolves, and brown bears. Polar bears occasionally den on the coastal plain. The ecoregion provides habitat for breeding shorebirds and waterfowl.
These gently rolling hills and broad exposed ridges form the northern flank of the Brooks Range. Narrow alluvial valleys and glacial moraines and outwash are interspersed among long, straight ridges and buttes of tightly-folded sedimentary rock. A dry, polar climate dominates the land, although it is slightly warmer and wetter than the Beaufort Coastal Plain. The surface is underlain with continuous permafrost. Solifluction slopes and stone stripes are common. Soils are usually saturated and have thick organic horizons. The soil in the lower foothills is frequently basic while the soil in the upper foothills is often acidic. Dominant vegetation classes include expanses of mixed shrub-sedge tussock tundra, willow thickets along rivers, and Dryas tundra on ridges. Calcareous areas support sedge-Dryas tundra. Lakes are infrequent but the region has many seasonally variable braided streams and rivers. Arctic char and arctic grayling are common. Herbivores include caribou, muskox, and arctic ground squirrels. Predators include peregrine falcons, gray wolves, and brown bears.
This east-west range is the northernmost extension of the Rocky Mountains and includes the Brooks Range, British Mountains, and Richardson Mountains. Many of the mountains are comprised of steep, angular summits flanked by rubble and scree. On the western and eastern ends of the range, the topography becomes less rugged. Rivers and streams cut narrow ravines into the terrain. During the Pleistocene, glaciers covered the higher portions of the range. Only a few small cirque glaciers remain. Permafrost is continuous on the northern side of the range. A dry, polar climate dominates the land. Winters are long and cold, and summers are short and cool. Air temperatures decrease rapidly with increased elevation. Dominant vegetation classes on the north side of the range are mixed shrub-sedge tussock tundra in valleys and lower slopes, willow thickets along rivers, and alpine tundra and barrens at higher elevations. The ecoregion provides habitat for dall sheep, caribou, marmots, gray wolves, and brown bears. Groundwater fed springs and streams provide habitat for arctic grayling.