This large ecoregion covers much of the interior Alaskan and Yukon forested area, extending from the Bering Sea on the west to the Richardson Mountains in the Yukon Territory on the east and bounded by the Brooks Range on the north and the Alaska Range on the south. The ecoregion includes an extensive patchwork of ecological characteristics due to local differences in topography, micro-climate, and drainage, but this finer mosaic of habitats is united into a single ecoregion by a predominance of spruce and hardwood forests, continental climate, and lack of Pleistocene glaciation. The terrain consists of rolling hills and lowlands dissected by nearly flat bottomlands along major rivers. Elevations range from sea level to approximately 600m, and slope gradients are usually less than 5 degrees. The unglaciated landscape of the Canadian portion of this ecoregion is generally flat to gently rolling, with low relief (300-600 m asl). The highest peak is 925 m asl and occurs in the Eagle Plains in the south (ESWG 1995).
Spruce-dominated coniferous forests cover the majority of the ecoregion and occupy a variety of site conditions. White spruce (Picea glauca) forests occur on warmer, drier sites on hillsides, in timberline areas, and along rivers. Black spruce (Picea mariana) is found in similar areas but has higher tolerance for poorly drained soils and extends into bottomlands and other wet areas. River meanders support a continuous succession of colonizing willow (Salix spp.) and alder (Alnus spp.), followed by balsam poplar (Populus balsamifera) and quaking aspen (Populus tremuloides), which are replaced by spruce. Recently disturbed sites, areas near timberline, north-facing slopes, and wetter areas support scrub communites dominated by willow, alder, and dwarf birch (Betula spp.) Bottomland bogs and other extremely wet areas are occupied by scrub-graminoid communities, including willow, dwarf birch, Labrador-tea (Ledum decumbens), bush cinquefoil (Potentilla fruticosa), and sedges (Eriophoum vaginatum and Carex spp.). Wildfire is very common throughout the ecoregion, and keeps a continuous mosaic of successional communities present, including herbaceous communities, scrub communities, and broadleaf, coniferous, and mixed forests (Bailey et al. 1994). Wetlands dominate the Old Crow Flats portion of the bioregion, comprised of polygonal peat plateau bogs with basin fens and locally occurring shore fens. Permafrost is continuous with medium to high ice content in the form of ice wedges and massive ice bodies.
The Interior Alaska/Yukon Taiga experiences a continental climate, with short, warm summers and long, cold winters. In general, annual temperature variance and precipitation increase from west to east. Average annual precipitation ranges from 250mm to 550mm, falling to 170mm in the upper Yukon flats. Average daily winter minimum temperatures range from -35°C to -18°C, and average daily summer maximum temperatures range from 17°C to 22°C (Gallant et al. 1995). The climate of the Canadian portion of this ecoregion is strongly continental considering its proximity to the Beaufort Sea. Mean annual temperature ranges from -10°C to -6.5° increasing toward the south. Mean winter temperature ranges from -27°C to -23.5°C, and summer temperature ranges from 7.5°C to 10°C. Mean annual precipitation is around 250 mm in the Old Crow areas, but increases up to 600 mm in the south. In general, this ecoregion has a high subarctic ecoclimate (ESWG 1995).
A wide range of soils occupy the many different ecological environments (for details, see Gallant et al. 1995). All are shallow above continuous to discontinuous permafrost, except along rivers. Parts of this ecoregion were left unglaciated in the Pleistocene, and formed part of the extensive Bering Sea Pleistocene refugium (Pielou 1994, Gallant et al. 1995).
The Interior Alaska/Yukon Lowland Taiga ecoregion has retained intact ecosystems, with healthy populations of all natural top predators. This is becoming increasingly rare in North America. The Porcupine, Central Arctic, and Western Arctic caribou herds migrate across, and winter in, this ecoregion. The rivers and wetlands of this ecoregion support breeding populations of many birds, including grebes, loons, and goldeneyes. Grouse (Dendragapus spp.) and flycatchers (Empidonax spp. and Contopus spp.) also breed in the river valley forests. Beaver (Castor canadensis), moose (Alces alces), caribou (Rangifer tarandus), and snowshoe hare (Lepus americanus) are common, as are mink (Mustela vison), river otter (Lontra canadensis), marten (Martes americana), and muskrat (Ondatra zibethica) along the major rivers. Other wildlife in this ecoregion includes grizzly bear (Ursus arctos), black bear (Ursus americanus), wolf (Canis lupus), red fox (Vulpes vulpes), raven (Corvus corax), osprey (Pandion haliaetus), bald eagle (Haliaeetus leucocephalus), golden eagle (Aquila chrysaetos), rock ptarmigan (Lagopus mutus), willow ptarmigan (L. lagopus), spruce grouse (Dendragapus canadensis), waterfowl, and chinook salmon (Oncorhrynchus tshawytscha), which spawn in the Porcupine River and its tributaries.
The Yukon Flats area in particular, in the northeastern corner of the ecoregion, is thought by McNab and Avers (1994) to be the most productive Arctic wildlife habitat in North America. In addition to supporting most of the above wildlife in dense numbers, it is home to lesser scaups (Aythya affinis), pintails (Anis acuta), scoters (Melanitta spp.), and widgeons (Anis spp.), as well as 15-20 percent of the canvasback (Aythya valisineria) population. Sandhill cranes (Grus canadensis) are common, and lynx (Lynx canadensis) are abundant. Minto Flats contains similar features and qualities to those of Yukon flats, but on a smaller scale.
A number of rare, narrowly endemic, or disjunct plant species also occur throughout this ecoregion, often associated with south-facing river bluffs. These species, including Cryptantha shakletteana, Erysimum asperum, and Eriogonum flavum are thought to be relicts from more widespread late Pleistocene tundra-steppe communities.
Habitat Loss and Degradation
This ecoregion is almost entirely intact, with little habitat loss or fragmentation. Habitat loss has occurred mainly surrounding human communities, especially Fairbanks, and in the Tanama Valley State Forest, which has experienced some clearcutting. Other forms of human disturbance include subsistence and recreational hunting (birds, terrestrial mammals) and fishing. Metallic element ore and sand and gravel deposits have been mined, and there has been limited agricultural use along major rivers. There has been little historic fragmentation, but this ecoregion, like most others in the Arctic, experiences enormous natural disturbances from fire, so blocks of intact habitat need to be large.
Occurrence of lightning-ignited wildfire is common throughout the ecoregion, and individual burns average about 20.00 km2 in area (6.85 km2 in the upper Yukon flats). Soils in this ecoregion are very susceptible to wildfire alteration, due to the relatively warm (-1.5°C) and shallow permafrost . Organic mat disturbance from wildfire can warm soils, significantly lower permafrost tables, alter soil properties and hydrology, and change vegetation composition (Gallant 1995).
Degree of Protection
The protected areas in Alaska were all designated by the Alaska National Interest Lands Conservation Act of 1980 and include large, intact areas of important lowland habitat. These areas generally contain significant inholdings owned by Alaska Native corporations. Important protected areas include the following:
•Yukon Flats National Wildlife Refuge - east-central Alaska
•Kanuti National Wildlife Refuge - central Alaska
•Koyukuk National Wildlife Refuge - west-central Alaska
•Innoko National Wildlife Refuge - western Alaska
•Nowitna National Wildlife Refuge - central Alaska
•Arctic National Wildlife Refuge - northeastern Alaska
•Vuntut National Park -northwestern Yukon Territory
Types and Severity of Threats
Major threats include:
•High likelihood of timber harvest in Tanana Valley State Forest and on native corporation lands. These harvests will not cover a significant portion of the ecoregion but will impact the highest volume stands disproportionately.
•Yukon Flats: much of this extraordinarily productive area is under native corporation ownership that may be open to timber harvests and oil and gas development in the future.
•Oil and gas development in Eagle Plains, Yukon Territory.
•High threat of exploitation of porcupine caribou herd from the Dempster Highway.
•Current wildlife management have been successful in managing game within natural range of variation, but potential exists for over-harvest or over-emphasis of management on game/commercial species.
Suite of Priority Activities to Enhance Biodiversity Conservation
•Tanama Valley State Forest: encourage sustainable harvest at lower levels than currently planned.
•Yukon Flats: acquire timber rights to critical areas or encourage sustainable practices
•Sucke, Bonnett-Plume, Wind Rivers that flow north into Peale River, then MacKenzie River are highly valued recreation rivers.
•Alaska Boreal Forest Council
•Canadian Parks and Wilderness Society, Yukon Chapter
•Friends of Yukon Rivers
•Northern Alaska Environmental Center
•World Wildlife Fund Canada
•Yukon Conservation Society
Relationship to other classification schemes
This ecoregion combines Gallant (1995) ecoregions 104, 106 and 107 with Ecological Stratification Working Group (1995) ecoregions 166, 167, and 169. It was determined that these three regions contained the same habitat mosaic elements, only in different proportions, so the aggregate consists of the same habitat variety linked by dominant commonalities as did the three contributing Gallant regions. In addition, much of the wildlife moves freely through and among the three component regions. Major delineation features are the dominance of forest cover, lowland to hilly terrain, and lack of Peistocene glaciation. Combination decisions based on Gallant et al. (1995) McNab and Avers (1994), Ecoregions Working Group (1989), Viereck, et al (1992), and Kuchler (1985).
Although most of this ecoregion lies in the state of Alaska, it encompasses the Old Crow Basin, the Old Crow Flats, and the Eagle Plains (TEC 166-167 and 169) in Yukon Territory on the Canadian side of the border (Ecological Stratification Working Group 1995). Vegetation here is considered Boreal Alpine Forest-Tundra (33) (Rowe 1972).
Prepared by: R. Hagenstein, T. Ricketts, J. Peepre, M. Sims, K. Kavanagh and G. Mann.