Ahklun and Kilbuck Mountains

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Located in southwestern Alaska off Bristol and Kuskokwim Bays, the 51,000-km2 ecoregion is composed of steep, sharp, often ringlike groupings of rugged mountains separated by broad, flat valleys and lowlands (fig. 24). The mountains were glaciated during the Pleistocene epoch, but only a few small glaciers persist. Dwarf scrub communities are the predominant vegetation cover in the mountains. Tall scrub and graminoid herbaceous communities are common in valleys and on lower mountain slopes. Valley bottoms may support stands of spruce and hardwood species.

Needs map



Climate

Climate is affected by both maritime and continental influences. Average annual precipitation ranges from 1,020 mm in the lowlands to 2,030 mm in the higher mountains. Average annual snowfall ranges from 205 cm to 510 cm, with a similar distribution pattern. Winter temperatures have an average daily minimum of -16°C and a maximum of -8°C. Mean summer temperatures have daily lows averaging about 8°C and daily highs of about 16°C to 19°C.

Physiography/landform

This mountainous ecoregion is composed of strongly deformed sedimentary and volcanic rocks of late Paleozoic and Mesozoic age and includes some bodies of older schist. Ringlike mountain groupings have resulted from small granitic masses surrounded by more resistant hornfels. Slope gradients over most of the region are from 0° to 8°, but steeper slopes are not uncommon (occurring across 7 percent of the area), and summits are very steep and sharp. Broad lowlands separate mountain groups. Regional elevations rise from sea level to more than 1,500 m. Streams are generally shallow and have radial drainage patterns; most are incised in bedrock gorges. A number of long, narrow, and often deep glacial lakes have formed in U-shaped valleys. The region was heavily glaciated during the Pleistocene epoch, and a few small cirque glaciers persist on higher mountains. Permafrost is discontinuous at higher elevations, and isolated masses occur at lower elevations.

Soil

Principal soils are Histic Pergelic Cryaquepts, Pergelic Cryaquepts, Typic Cryochrepts, Lithic Cryumbrepts, Pergelic Cryumbrepts. Pergelic Cryorthods. Typic Haplocryods, and Typic Humicryods. Mountain soils formed in very stony and gravelly colluvial material over bedrock. Valleys soils formed in glacial till.

Hydrology

Shallow, mostly high-gradient streams, with radial drainage patterns are found, often, incised in bedrock gorges. The region also features a few long, narrow, deep glacial lakes in U-shaped valleys.

Geology

Flora

Upper slopes and summits of mountains are exposed to harsh climatic conditions. Lower slopes and valleys offer more protected sites for vegetation establishment. Dwarf scrub communities are widespread in the mountains (fig. 25). Valleys provide an array of soil drainage conditions that support different vegetation communities (fig. 26). Sites with better drainage support needleleaf, broadleaf and mixed forest stands, and tall scrub communities. Mesic graminoid herbaceous communities occur over a range of dry to wet soils. The wettest sites are colonized by low scrub communities and wet graminoid herbaceous communities.

Dwarf scrub communities are dominated either by ericaceous shrubs (for example. Arctostaphylos alpina, Vaccinium vitis-idaea, V. uliginosum, Empetrum nigrwn, and Ledum decumbens), or by a mix of mountain-avens (Diyas octopetala) and dwarf arctic birch (Betula nand). Lichens (for example, Cladina spp., Cetraria spp., Stereocaulon tomentosum, Thamnolia vermicularis, Cladonia spp., and Alectoria spp.) may be sparse or may codominate with shrubs.

Valley bottoms may support needleleaf forests dominated by white spruce, broadleaf forests dominated by balsam poplar (Populus balsamifera), or mixed forests of white spruce and paper birch (Betula papyri/era). White spruce forests are dominated by Picea glauca. Resin birch (Betula glandulosd) dominates the low shrub layer. Common herbs include Linnaea borealis, Calamagrostis canadensis, and Equisetum spp. A nearly continuous cover of feathermosses (for example, Pleurozium schreberi and Hylocomium splendens) is typical. Lichens (for example. Cladonia spp.) are particularly common in open areas.

Balsam poplar forests are dominated by Populus balsamifera in the overstory. Understory composition varies, usually including willow (Salix spp), alder (Alnus spp.), high bushcranberry (Viburnum edule), prickly rose (Rosa acicularis), bluejoint (Calamagrostis canadensis), and feathermosses (Hylocomium splendens and Pleurozium schreberi).

Spruce-paper birch forests are dominated by white spruce (Picea glauca) and paper birch (Betula papyri/era). Shrubs, such as willow (Salix bebbiana and S. scouleriana), alder (Alnus crispa), prickly rose (Rosa acicularis), and high bushcranberry (Viburnum edule), are common. Typical herbs are bluejoint (Calamagrostis canadensis) and horsetail (Equisetum arvense). Cover by mosses (for example, Hylocomium splendens, Dicranum spp., Hypnum spp., and Rhacomitrium spp.) is patchy.

Tall scrub communities are dominated by willow (for example, Salix alaxensis, S. planifolia, and S. glauca). alder (for example, Alnus crispa and A. sinuata), or a mix of ericaceous shrubs (for example, Empetrum nigrum, Ledum decumbens, Vaccinium vitis-idaea, V. uliginosum, and Arctostaphylos alpina), dwarf arctic birch (Betula nand), and sedges (for example, Carex spp.). Mosses (for example, Hypnum spp., Dicranum spp., and Polytrichum spp.) may be common or absent.

Mesic graminoid herbaceous communities are dominated by bluejoint (Calamagrostis canadensis), which forms meadows that may include other herbaceous species (for example, Carex spp., Eriophorum spp., and Epilobium angustifolium). Low scrub communities include low scrub-sedge tussock bogs, ericaceous scrub bogs, and low sweetgale-graminoid bogs.

Low scrub-sedge tussock bogs are codominated by low woody plants (for example, Betula glandulosa, B. nana, and Vaccinium vitis-idaed) and tussock-forming sedges (for example, Eriophorum vaginatuni). Mosses (for example, Sphagnum spp. and Rhacomitrium spp.) provide a nearly continuous mat between tussocks.

Ericaceous scrub bogs are dominated by Empetrum nigrum, Vaccinium vitis-idaea, V. uliginosum, V. oxycoccus, and Ledum decumbens. Sedges (for example, Carex spp. and Trichophorum caespitosum) are common or codominant. The moss layer is usually dominated by Sphagnum species, though other species (for example, Dicranum spp.) may be common. Lichens (for example, Cladina spp.} are present on mounds.

Sweetgale-graminoid bogs are dominated by sweetgale (Myrica gale), bluejoint (Calamagrostis canadensis), sedges (Carex spp.), and clubrush (Trichophorum caespitosum). Other woody and herbaceous species may be present. Mosses (for example, Sphagnum spp., Rhacomitrium spp., and Hypnum spp.) are abundant.

Wet graminoid herbaceous communities include sedge wet meadows and sedge-moss bogs. Several species of sedge (for example, Carex aquatilis and C. lyngbyaei) dominate sedge wet meadows. Sedge-moss bogs are dominated by mosses (principally Sphagnum spp.) and low sedges (for example, Eriophorum russeolum, Carex spp., and Trichophorum caespitosum).

Plant Species List

Wildfire

Occurrence of wildfires in the Ahklun and Kilbuck Mountains Ecoregion is very low. Recorded burns have ranged in size from less than 1 ha to 80 ha, averaging about 20 ha.

Fauna

Moose, brown bear, black bear, beavers, arctic hares, rainbow trout, sockeye, chum, king, and silver salmon, walruses, sea lions, blackpol warblers, seabirds, tundra swans, emperor geese, sandhill cranes are found.

Animal Species List

Birds:

Red-throated loon (Guvia stellata)

Pacific loon (Gavia pacific)

Common loon (Gavia immer)

Yellow-billed loon (Gavia adamsii)

Homed grebe (Podiceps auritus)

Fungi Species List

Algae

Lichens Species List

Ecosystems

Landuse/Human Activities

Permanent settlements are limited to the coastal margins of the ecoregion. The region has traditionally provided hunting and fishing resources to the people of the Bristol Bay and Yukon-Kuskokwim Delta Yup'ik groups. Their primary resources for subsistence have been salmon and freshwater fish, seals, and beluga whales. Terrestrial mammals, particularly caribou, provide a secondary resource. Migratory waterfowl and their eggs are an important source of food in early spring. Edible and medicinal plants are collected. Gold, silver, platinum, lead, mercury, zinc, and borax have all been mined in this ecoregion.

References

US Geological Survey. 1995. Ecoregions of Alaska, U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1567, Alisa L. Gallant, Emily F. Binnian, James M. Omernik, and Mark B. Shasby. UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON

United State Fish and Wildlife Service. 1991. Birds of the Kilbuck and Ahklun Mountain Region, Alaska BY Margaret R. Petersen Douglas N. Weir Matthew H. Dick. UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE North American Fauna 76 December 1991