Chapter 13
Ecological Subregions of the United States



Upper Yukon Tayga - Meadow

One Section has been delineated in this Province:

This Section is located in east-central Alaska, bordering Canada. Its area is about 68,400 mi2 (177,200 km2).

Section M139A--Upper Yukon Highlands

Geomorphology. The area mainly consists of rounded, low mountains and hills, interspersed frequently by valleys. Elevation ranges from 985 to 5,900 ft (300 to 1,800 m).

Lithology and Stratigraphy. The area consists of fragments of deep ocean floor and continental fragments composed of segments of the Yukon-Tanana, Kandik River, Porcupine, Tozitna, and Ruby terranes. Together these form a very complex geologic matrix.

Soil Taxa. The dominant soils are Ochrepts and Aquepts having a cryic or pergelic temperature regime. Upland soils beneath spruce-birch-aspen forests are commonly Cryochrepts. Black spruce and tundra vegetation, characterized by sedges, usually occurs on Cryaquepts. Cryumbrepts, Cryorthents, and Cryorthods also occur, mainly in alpine areas with tundra vegetation.

Potential Natural Vegetation. The vegetation pattern of this area is complex. Forests of white spruce, birch, and aspen dominate most lower slopes in the south and south-facing slopes in the north. Black spruce forests typically grow at higher elevations, on all north-facing slopes in the south, and on all but steep south-facing slopes in the north. Black spruce forests also occur at lower elevations where drainage is impeded. Highest elevations are either barren or have tundra vegetation, with sedge and mosses dominating poorly drained sites and low-growing shrubs on drier sites (e.g., scrub birch and willow).

Fauna. The open, mixed deciduous-conifer forests of the upper Yukon Highlands support a large variety of birds that are characteristic of this Section. Commonly occurring breeding birds include gray jays, boreal chickadees, northern flickers, red-tailed hawks, and boreal owls. Sharp-tailed grouse and upland sandpipers, although considered uncommon, are also characteristic of this area. Hoary marmots occur in the mountainous areas, while woodchucks are found in the lower, open woodlands. This Section provides prime habitat for Arctic ground squirrels and northern flying squirrels. The range of long-tailed and yellow-cheeked voles in interior Alaska corresponds closely with this Section. Upland furbearers, such as marten, mink, and short-tailed and least weasels, are common. Dall sheep are associated with the high, mountainous areas. Caribou from the Delta and Fortymile herds are found here. Bison were introduced into the area in 1928. Wood frogs have been reported in this Section. Northern pike are common in the larger lakes and rivers, while Arctic grayling are more abundant in smaller streams. Climate. Average annual precipitation ranges from 6 to 14 in (150 to 360 mm). Average annual temperature ranges from 13 to 25 _o_F (-11 to -4 _o_C). The growing season lasts approximately from May 15 to September 10. It is probably much shorter at high elevations.

Surface Water Characteristics. Many streams traverse the Section, although extensively rugged areas have little surface water. Some lakes occur in broader valleys. Midsummer soil moisture deficiencies frequently occur on well drained sites. Most valley bottoms, north-facing slopes, and hills greater than 2,625 ft (800 m) are underlain by permafrost. Soils are normally wet or moist under these circumstances. Wetlands occupy about 40 percent of the area.

Disturbance Regimes. Wildfire is a very common disturbance factor due to the relatively warm and dry summer climate and frequent lightning storms.

Land Use. Human disturbance is mainly restricted to subsistence and recreational hunting, although there is occasional mining.

Cultural Ecology. Kutchin, Koyukon, Tanana, Tanacross, Han, and Upper Tanana Athabaskins reside in this Section.

Compiled by Alaska Region.