The assessment area includes seven ecoregions in interior Alaska: the Brooks Range (south of the ridge crest), Kobuk Ridges and Valleys, Ray Mountains, Davidson Mountains, North Ogilvie Mountains, Yukon – Old Crow Basin, and Yukon-Tanana Uplands. The assessment boundary, following BLM guidelines, constitutes the seven component ecoregions and any 5th level hydrologic units that intersect the ecoregion boundaries. This was agreed to by the BLM to facilitate seamless integration with neighboring REA efforts and to ensure that regionally important resources that may exist just outside of the ecoregion boundaries are included in the analysis. Several Highway systems traverse the study area. The study area includes the metropolitan area of Fairbanks, smaller road accessible communities, and communities that lack road access. Seven major river systems traverse the study area: the Noatak, Kobuk, Koyukuk, Tanana, Charley, Porcupine, and Yukon rivers. The ecoregional descriptions below are paraphrased from Unified Ecoregions of Alaska (Nowacki et al. 2001).
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. 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. Permafrost is mostly continuous south of the ridge crest. Dominant vegetation classes on the south side of the range are sedge tussocks and shrubs in valleys and lower slopes, sparse conifer-birch forests in large valleys, 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.
Kobuk Ridges and Valleys
The Kobuk ridges and valleys ecoregion is comprised of a series of paralleling ridges and valleys that radiate south from the Brooks Range, created partially by high-angle reverse faults and interceding troughs. In the past, ice sheets descending from the north covered the area. Broad valleys are covered with alluvial and glacial sediments while intervening ridges are covered with rubble. Climate is dry continental with long, cold winters and short, cool summers. During winter, cold air drains from the Brooks Range into the valleys. Permafrost is thin to moderately thick throughout much of the area. Forests and woodlands dominate much of the area. Trees become increasingly sparse in the west. Tall and short shrub communities of birch, willow, and alder occupy ridges.
The Ray Mountains are comprised of compact, east-west oriented ranges. Metamorphic bedrock is covered with rubble, and soils are shallow and rocky. During the Pleistocene, the Ray Mountains remained largely unglaciated. Climate is continental with dry, cold winters and somewhat moist, warm summers. Permafrost is discontinuous and ranges from thin to moderately thick. Dominant vegetation classes are black spruce woodlands; white spruce, birch, and aspen on south-facing slopes; white spruce, balsam poplar, alder, and willows on floodplains; and shrub birch and Dryas-lichen tundra at higher elevations. Clear headwater streams are important habitat for arctic grayling. Moose, brown bears, gray wolves, red fox, lynx, and marten are common.
Mountains with coarse rubble slopes are interspersed with broad floodplains underlain by unconsolidated glacial and alluvial sediments. Thin to thick permafrost underlies the majority of the ecoregion. Climate is continental with cold winters and short, cool summers. Dominant vegetation classes are black spruce woodlands; white spruce and balsam poplar along rivers; and white spruce, resin birch, and quaking aspen in uplands. Shrub communities of willow, alder, and birch are also common. Forest fires are frequent. Moose, bears, and wintering caribou are common.
North Ogilvie Mountains
Flat-topped hills and a plain are primarily underlain by calcareous sedimentary rock. The ecoregion was not glaciated and is therefore heavily eroded. Ridges and upper slopes are barren and jagged rock outcrops are common. Shallow soils cover the rocky colluvial deposits of slopes that are subject to frequent landslides and debris flows. Lower and more stable slopes have developed deeper soils that are extensively underlain by permafrost. Low shrub tundra with willow, alder, and birch and spruce woodlands occur at lower elevations. The streams originating in the North Ogilvie Mountains feed the Porcupine, Yukon, and Peel rivers. Few lakes exist. Climate is continental with cold winters and short, cool summers. Brown bears, wolverine, dall sheep, caribou, lemmings, and pikas are common.
Yukon – Old Crow Basin
Mountain toeslopes around the Porcupine River form a basin comprised of depositional fans, terraces, and pediments. The region was largely unglaciated and is heavily eroded. Surrounding the flats, surficial deposits of colluvial, alluvial, and aeolian origins are deep and underlain by continuous permafrost. The poorly drained flats contain extensive wetlands with many thaw lakes and ponds. Deltaic fans, river terraces, and floodplains are common on the landscape. Climate is dry continental with large seasonal temperature fluctuations. Winters are cold and dry because of dominant arctic high pressure systems. Common vegetation ranges from wet herbaceous marshes to open black spruce forests to closed spruce-deciduous forests on well-drained uplands. The wetland complexes formed by the Yukon River support large numbers of waterfowl and other migratory birds. Moose, bears, northern pike, and salmon are common.
Broad, rounded mountains of moderate height are underlain by metasedimentary volcanic crust blocks and continental shelf deposits. Surficial deposits are bedrock and rubble on ridges and upper slopes, colluvium on lower slopes, and alluvium in the narrow valleys. The region is underlain by discontinuous permafrost thick on north-facing slopes and thin in valleys. Climate is continental with cold winters and warm summers. White spruce, resin birch, and quaking aspen dominate south-facing slopes. North-facing slopes are primarily black spruce woodland or forest while valleys are dominated by black spruce woodlands and tussock bogs. Low birch – ericaceous shrub and Dryas-lichen tundra are common at the uppermost elevations. Forest fires are very common in this region resulting in a patchwork of forest ages. Caribou, moose, snowshoe hare, marten, lynx, black bears, and brown bears are common. Abundant cliffs provide habitat for peregrine falcons. Chinook, chum, and coho salmon spawn in the clear headwater streams.