Chapter 10
Ecological Subregions of the United States



Upper Yukon Tayga

One Section has been delineated in this Province:

Located in east-central Alaska, the area of this Section is about 13,000 mi2 (33,700 km2).

Section 139A--Upper Yukon Flats

Geomorphology. The Yukon Flats encompass gently sloping outwash fans and floodplains of the Chandalar, Christian, Sheenjek, and Upper Yukon Rivers. This Section is a relatively flat, marshy basin patterned by braided and meandering streams, numerous thaw and oxbow lakes, and meander scars. Elevation ranges from 300 to 820 ft (90 to 250 m).

Lithology and Stratigraphy. Post-accreted alluvial fan and basin fill deposits of late Tertiary and Quaternary age occur.

Soil Taxa. Principal soils are Histic Pergelic Cryaquepts, Pergelic Cryaquepts, Aquic Cryochrepts, and Pergelic Cryochrepts. Most soils formed from silty alluvium and loess deposits. Lower parts of the floodplain are poorly drained and covered with peat, whereas natural river levees are better drained.

Potential Natural Vegetation. Bottomland spruce-aspen-birch grow on the better drained alluvial sites. Alder and willow form thickets on newly exposed alluvial sites, which are subject to periodic flooding. The wettest sites have black spruce, willow, or graminoid marsh cover.

Fauna. The Yukon Flats may be the most productive Arctic habitat for wildlife on the continent. Predominant waterfowl species that breed in the Section are the lesser scaup, pintail, scoter, and widgeon. This area also supports 15-20 percent of the diminished population of canvasbacks. Arctic, red-throated, and common loons, horned and red-necked grebes, and sandhill cranes are also common. The snowshoe hare and lynx may be abundant in this Section but experience population cycles. This area provides prime habitat for aquatic furbearers, including river otters, beaver, and muskrats. Wood frogs have been reported from this Section. King, silver, and chum salmon occur in the Yukon River and its tributaries. Resident fish include northern pike, sheefish, burbot, and Arctic grayling.

Climate. Average annual precipitation ranges from 7 to 13 in (180 to 330 mm). Average annual temperature ranges from 16 to 24 _o_F (-9 to -4 _o_C). The growing season generally lasts from May 15 to September 10; however, freezing can occur in any month.

Surface Water Characteristics. Surface water in streams, lakes and bogs is usually abundant. Water levels of lakes are typically not maintained by precipitation, but rather by spring flooding. All poorly drained soils are underlain by perennially frozen ground. Wetlands occupy 38 percent of the area.

Disturbance Regimes. Wildfire occurrence is common in the Yukon Flats. Land Use. The area is populated by several small villages. Subsistence and recreational hunting and fishing are the primary human uses.

Cultural Ecology. Koyukon and Kutchin Athabaskans occupy the western and eastern portions of the basin, respectively.

Compiled by Alaska Region.