Interior Yukon-Alaska alpine tundra

Category: Grassland, Tundra, and Human Biomes.

Geographic Location: North America.

Summary: This cold, harsh region has limited biodiversity, but important populations of certain wildlife species.

The south-central Yukon Territory in Canada and east-central Alaska in the United States form a contiguous ecoregion of alpine, subalpine, and boreal northern cordilleran regions. The prevailing climate here is one of short, cool summers averaging 50 degrees F (10 degrees C) and long, cold, dark winters with mean temperatures of minus 4 degrees F (minus 20 degrees C). Tree growth in this tundra biome is limited by the year-round low temperatures and short growing season.

In Russian, tundra means treeless uplands, though it is generally applied only when such areas have permafrost. The Yukon-Alaska Interior Alpine Tundra biome is the home of the coldest recorded temperature in North America of minus 81 degrees F (minus 63 degrees C), measured on the Kluane Plateau.

The ecoregion was heavily shaped by glacial movement and includes mountain ranges with peaks of 6,890–7,874 feet (2,100–2,400 meters), rolling hills, and incised plateaus separated by valleys and lowlands. Permafrost is common, especially in the north and at the highest elevations; on the coast, it is only sporadic. In the rain shadow of the coastal mountains, precipitation is less than 12 inches (0.3 meter) per year, but it is about 2 feet (0.6 meter) on the plateaus.

Vegetation

Alpine tundra vegetation has adapted to survive the low temperatures, limited water availability (though not as limited as in desert biomes), and increased exposure to ultraviolet radiation that are associated with higher elevations. The lower elevations of the Yukon-Alaska Interior Alpine Tundra region include forests as well, which thin out rapidly as elevations increase. The most common trees here are forests of black and white spruce (Picea mariana and P. glauca), in a matrix of quaking aspen (Populus tremuloides) or dwarf willow (Salix), as well as birch (Betula) and shrubs (Ericaceae).

In the lowlands, where drainage is poor, forests are predominantly black spruce, scrub willow, and birch. Floodplains are covered with balsam poplar (P. balsamifea). The permafrost slopes are home to forests of black spruce, willow, and paper birch (Betula papyrifera). At higher elevations, the vegetation is sparse and includes dwarf willow; birch; graminoid, or grass, species in the Gramineae and Cyperaceae genera; mosses; and mountain avens (Dryas hookeriana).

Other, less-common trees include the lodgepole pine (Pinus contorta) and subalpine fir (Abies lasiocarpa). Understory vegetation and vegetation at upper elevations use deep root systems to avoid water loss and reach maximum stomatal opening at midday, when the temperature is warmest. Ultraviolet radiation may be a contributing factor in stunting the growth of alpine tundra plant life; studies are inconclusive.

Many of the plant species in the tundra are food plants for psyllids, or jumping plant lice, of which there are seven families: Aphalaridae, Calophyidae, Carsidaridae, Homotomidae, Phacopteronidae, Psylllidae, and Triozidae. Much of the region’s species richness is in the phyllidae superfamily, in fact. Willows feed the greatest number of species; a willow stand may be home to more than one dozen species of plant lice. The lice feed on the living, nutrient-rich tissue, called pholem, of vascular plants. On a willow tree, this tissue is the innermost layer of the bark; the bark helps protect lice from the cold.

Many of the flowering plants of the region form their flowers early, in a process called preformation, so that they can flower immediately when the snow begins to thaw. Plants that undergo preformation protect their preformed inflorescence from frost damage in the winter by surrounding themselves with tightly packed leaves covered in hair, which serve as insulation. The advantage of flowering early is that any successfully germinated seeds have a longer period of time in which to mature before the next frost. Because few pollinators are available, though, their reproductive success is limited.

The opposite approach is attempted by late-flowering plants, which produce a large number of seeds toward the end of the brief spring. Most of the plants that grow from those seeds will die, but so many seeds are produced that some survivors will beat the poor odds. Plants using this adaptation tend to be self-pollinators.

At higher altitudes, flowering is less common; clonal propagation of grasses and reproduction by spores, as in the case of cryptogams (ferns, lichens, algae, and mosses), are more successful. Moss and lichens can flourish in the semiarid frigid biomes of the higher elevations, where wind, cold, snow, and soil quality make life difficult for other plants.

Wildlife

Wildlife includes grizzly and black bears (Ursus arctos and U. americanus), Dall’s sheep (Ovis dalli), caribou (Rangifer tarandus), moose (Alces alces), red foxes (Vulpes fulva), wolves (Canis lupus), hares (Lepus spp.), ravens (Corvus corax), rock and willow ptarmigans (Lagopus mutus and L. lagopus), and golden eagles (Aquila chrysaetos).

The endemic (not found elsewhere) subspecies of caribou in the region is the porcupine caribou (Rangifer tarandus granti), named for the Porcupine River, which runs through its habitat. In 2017, the porcupine caribou herd numbered about 197,000, with the caribou migrating 1,500 miles (2,414 kilometers) every year between their calving grounds in and near the Arctic National Wildlife Refuge and the Yukon-Alaska alpine tundra; this is the longest land migration route of any terrestrial mammal.

Threats

Most of the region remains intact. Road development and mining have contributed to degradation of about 15 percent of the area, mostly in valley bottoms that have been altered by mining activity. The Yukon contains no protected areas. Eastern Alaska includes four protected areas: the Yukon-Charley Rivers National Preserve, Streese National Conservation Area, White Mountains National Recreation Area, and Arctic National Wildlife Refuge. These cover primarily the lowlands and do not include the alpine uplands surrounding them.

Climate change impacts in this biome may be seen in the permafrost, where scientists can measure warming trends. When permafrost melts, it can release greenhouses gases such as methane and carbon dioxide, contributing to a positive feedback loop that adds to the overall greenhouse effect, thereby accelerating further permafrost melting.

Bibliography

Hulten, Eric. Flora of Alaska and Neighboring Territories. Palo Alto, CA: Stanford University Press, 1968.

MacLean, S. F. and I. D. Hodkinson. “The Distribution of Psyllids (Homoptera: Psylloidea) in Arctic and Subarctic Alaska.” Arctic and Alpine Research 12, no. 3 (1980).

"Porcupine Caribou News." Alaska Department of Fish and Game, 2017, www.adfg.alaska.gov/static/home/library/pdfs/wildlife/porcupine‗caribou‗news/porcupine‗caribou‗news‗summer‗2017.pdf. Accessed 8 Aug. 2022.

Rand, A. L. “The Ice Age and Mammal Speciation in North America.” Arctic 7, no. 1 (1954).

Scudder, G. G. E. “Present Patterns in the Fauna and Flora of Canada.” Memoirs of the Entomological Society of Canada 111, no. 108 (1979).