139 Upper Yukon Tayga Province

Yukon Flats, 13,000 mi2 (33,700 km2)


Land-surface form.--This province is mostly a flat plain consisting of marshy lake-dotted flats rising from 300 ft (90 m) in altitude in the west to 600-900 ft (180-270 m) in the north and east. The province is made up of outwash fans and floodplains of the Chandalar, Christian, Sheenjek, and Upper Yukon Rivers. Rolling silt- and gravel-covered marginal terraces with sharp escarpments 150-600 ft (50-180 m) high rise above the flats, sloping gradually upward to altitudes of about 1,500 ft (460 m) at the base of surrounding uplands and mountains.

Climate.--The climate is the extreme continental boreal type, with its large annual temperature range, severely cold winters, and short, hot summers. The average daily minimum temperature of the coldest month is -29F (-33C). At Fort Yukon, more than 130 days per year have a minimum temperature of 0F (-18C) or below. The record low at Fort Yukon is -78F (-61C), and the record high is 100F (38C). The growing season is less than 3 months. The region is semiarid, with an average annual precipitation of about 7 in (179 mm), with a summer maximum. Snowfall averages 45 in (1,150 mm) per year.

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

Soils.--Principal soils are wet Inceptisols, mostly in flats and low areas. Lower parts of the floodplains are poorly drained and covered with peat, whereas river terraces are better drained.

Fauna.--The fauna of the Yukon Flats Province are similar to those in other tayga regions. But this province provides what may be the most productive arctic habitat for avian wildlife on the continent. Predominant waterfowl species that breed in the region include the lesser scaup, pintail, scoter, and wigeon. The area supports 15-20 percent of remaining canvasbacks. Arctic, red-throated, and common loons, horned and red-necked grebes, and sandhill cranes are also common. Cliffs along the Yukon and Porcupine Rivers support several raptor species, including osprey, gyrfalcon, Swainson's hawk, and the endangered American peregrine falcon.