
Natural Resources
Conservation Service
Ecological site YX244X00A202
Arctic Mountain Valley Floodplains
Last updated: 5/28/2025
Accessed: 10/19/2025
General information
Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
MLRA notes
Major Land Resource Area (MLRA): 244X–Northern Brooks Range Mountains
Major Land Resource Area (MLRA) 244X includes the steep, rugged, high mountains and narrow valleys on the northern side of the Brooks Range. This remote wildland is sparsely populated and is approximately 14,525 square miles (37,615 square kilometers). The transition to the Arctic climate is the break into MLRA 244X from the surrounding subartic MLRAs. Elevation ranges from about 1,969 feet (600 meters) to 8,570 feet (2,613 meters) at the summit of Mount Igikpak. The major rivers are the Kongakut, Aichilik, Jago, Canning, Ivishak, Ribdon, Atigun, Anaktuvuk, and Killik Rivers. They drain to the Colville River and Arctic Ocean.
Except for the highest peaks, the steep upper ridges, and some unglaciated valleys, glacial ice during the Early and Middle Pleistocene covered the MLRA. By the Late Pleistocene, only the highest valleys and mountains remained glaciated. Periglacial features (gelifluction lobes, polygons, and stripes) and fluvial deposits are common on terraces and gentle slopes. Glacial deposits overlay stratified sedimentary bedrock. This area is in the zone of continuous permafrost. Inclusions of volcanic and igneous rocks occur in the eastern part of the MLRA.
The Brooks Range is characterized by continental arctic climate. The average annual precipitation ranges from 7 to 40 inches (180 to 1,015 millimeters) with an average annual snowfall of 50 to 100 inches (125 to 255 centimeters). The average annual temperature ranges from 8 to 16 degrees Fahrenheit (-13 to -9 degrees C), with freezing temperatures possible any month of the year. Summer temperatures reach 90 to 100 degrees Fahrenheit (32 to 38 degrees Celsius), and winter temperatures drop as low as -75 degrees Fahrenheit (-60 degrees Celsius). The position of this MLRA above the Arctic Circle lends to several days of 24-hour sunlight in June and several sunless days in December.
Freshwater is very limited due to frozen or low flow through long winters. Most domestic use water is from private wells. Aquifers are highly susceptible to contamination from surface activities (septic systems, landfills, and leaking fuel storage tanks).
The dominant soil order in this MLRA is Gelisols. The main soils are Aquiturbels, Histoturbels, Molliturbels, and Haploturbels. These are shallow or moderately deep to permafrost, poorly- to very poorly- drained, and formed in colluvium, slope alluvium, and residuum. Fibristels are shallow or moderately deep to permafrost, very poorly drained, and formed in thick deposits of organic material; in depressions, drainageways, and basins. Miscellaneous areas make up about 75 percent of this MLRA primarily composed of rubble, chutes, rock outcrops, and small glaciers. Lakes make up less than two percent of the area
Low willow, ericaceous shrub scrub, and tussocks are most dominant at lower elevations, with wet sites supporting wet meadows and willow scrub. Dwarf scrub communities (black crowberry, ericaceous shrubs, Dryas, and dwarf willow) are prominent on mountain slopes and ridges with exposed areas dominated by lichens, forbs, sedges, and mosses. As elevation and exposure increase, vegetation disappears and is replaced by rubble, talus, and other miscellaneous areas. This elevational transition is highly variable but roughly occurs at 6,500 feet (Zou et al. 2023) where glaciers also commonly prevail.
Villages use this remote area primarily for subsistence. Mining and prospecting of mineral resources historically occurred. Current disturbance relates to the pipeline and construction of Dalton highway. This disturbance of the fragile permafrost-affected soils is of increasing concern.
LRU notes
No LRUs are developed for this Major Land Resource Area (MLRA). Soils that are within this area are maintained as arctic. Soils corresponding to boreal communities are correlated to the appropriate adjacent MLRA.
Classification relationships
The Brooks Range is the most northerly extension of the Rocky Mountains occurring within the Arctic Mountains province of the Rocky Mountain System.
Description of the Ecoregions of the United States (Bailey 1983)
100 Polar Domain
120 Tundra Division
M120 Tundra Division - Mountain Provinces
M121 Brooks Range Tundra--Polar Desert Province
United States National Vegetation Classification
C04. Polar & High Montane Scrub, Grassland & Barrens Class
S12. Temperate to Polar Alpine & Tundra Vegetation Subclass
F031. Polar Tundra & Barrens Formation
D044. Arctic Tundra & Barrens Division
M173. Feltleaf Willow - Eight-petal Mountain-avens - Tussock Cottongrass
Tundra Macrogroup
G896. Arctic Dwarf-shrub Tundra Group
A4336. Arctic Nonacidic Dwarf Willow Tundra Alliance
LandFire BpS Model/Description Version: Nov. 2024
- 17150 Alaska Arctic Floodplain
Ecological site concept
- This arctic ecological site occurs on floodplains in the Northern Brooks Range MLRA.
- Soils formed in intermixed silty, sandy, and gravelly alluvium.
- Soils are very deep. These gravelly soils lack permafrost in the soil profile.
-Soils flood frequently to occasionally. These poorly and somewhat poorly drained soils have a water table at very shallow to moderate depths during the growing season.
- Vegetation is intermixed patches of scrubland dominated by willow and/or entireleaf mountain-avens and areas with a high water table dominated by wet herbaceous graminoid meadows.
Associated sites
YX244X00A204 |
Arctic Mountain Valley Terraces Terraces occur along major drainages and are a transitional step up in elevation from the more pronounced floodplains. The shrub-tussock community of the terrace blends down to floodplain vegetation, which does not include dominant tussocks. |
---|
Similar sites
YX244X00A111 |
Arctic Mountain Hummocks The arctic mountain ponds may occur on and will have similar species as wetter portions of the floodplain, especially in concave depressions and along the channel edge. |
---|
Table 1. Dominant plant species
Tree |
Not specified |
---|---|
Shrub |
(1) Salix pulchra |
Herbaceous |
(1) Chamerion latifolium |
Legacy ID
R244XY202AK
Click on box and path labels to scroll to the respective text.
Ecosystem states
State 1 submodel, plant communities
CP 1.1A | - | Increase water table |
---|---|---|
CP 1.2B | - | Decrease water table |