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Ecological site R246XY009AK

Arctic High-Center Polygon Complex

Last updated: 5/22/2025
Accessed: 10/19/2025

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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): 246X–Arctic Coastal Plain

The Arctic Coastal Plain MLRA (MLRA 246X) consists of level to gently rolling plains along the coast of the Arctic Ocean. This area makes up 22,235 square miles. It is mostly remote, sparsely populated wildland. Numerous rivers, mostly originating in the Brooks Range, drain to the Arctic Ocean. The largest being the Canning, Colville, Jago, Kongakut, Kuk, Utukok, and Sagavanirktok Rivers. Narrow, nearly level flood plains and stream terraces parallel the many rivers. The area is dotted by thousands of small and medium-size lakes and interconnecting wetlands. Many of the lakes are elongated thaw lakes, which are consistently oriented from north to northwest. Small sand dunes occur along the coastline, rivers, and plains. Elevation ranges from sea level to about 655 feet.

Permanent settlements include Point Lay, Wainwright, Utqiagvik, Nuigsut, and Kaktovik. The Prudhoe Bay oil fields and the northern terminus of the Trans-Alaska Pipeline are in the central part of the MLRA. The Dalton Highway and the Trans-Alaska Pipeline bisect the area west of the Sagavanirktok River, terminating at Deadhorse. The community of Deadhorse provides much of the industrial infrastructure and many of the residential facilities associated with the oil fields and pipeline. Parts of the National Petroleum Reserve and Arctic National Wildlife Refuge are in this MLRA.

Geology and Soils

This area was never glaciated (NRCS 2022). The bedrock geology consists of Cretaceous and Tertiary stratified sedimentary rocks and uplifted continental deposits. The modern landscape is mantled with Quaternary deposits of alluvial, eolian, or glaciofluvial origin.

This MLRA is in the zone of continuous permafrost. Areas without permafrost in the soil profile are limited to tidal flats, large sand dunes, and soils directly adjacent to large rivers. Thick layers of permafrost occur in both fine textured and coarse textured deposits across the area. Depth to the base of the permafrost layer ranges between 500 and 2000 feet. Periglacial features, such as beaded drainages, patterned ground (ice-wedge polygons, thaw gullies, pingos, and frost boils) occur throughout the MLRA.

The dominant soil order in this MLRA is Gelisols. Most have an aquic soil moisture regime. The Gelisols are shallow or moderately deep to permafrost, occur on fine and coarse textured sediments, and are generally poorly drained or very poorly drained. Common Gelisol suborders are Histels, Orthels, and Turbels. The Histels have a glacic layer and/or thick accumulations of surface organic material and are associated with ice-wedge troughs of polygons, vegetated lake basins, swales, and low-gradient drainageways. The Orthels and Turbels have comparably thinner surface organic material and occur on flood plains, stream terraces, plains, and the centers of low- and high-center polygons. Miscellaneous (non-soil) areas make up about 20 percent of this MLRA. The most common are water, riverwash, and beaches.

Climate
The average annual precipitation in this area is 4 to 8 inches. Brief, cool summers and long, very cold winters characterize the arctic climate. The average annual snowfall is about 20 to 40 inches. The average annual temperature ranges from 11 to 14 degrees Fahrenheit. The average freeze-free period is between 43 and 76 days but freezing temperatures can occur in any month.

Vegetation
The wet soils prevalent across this MLRA support extensive swaths of tussock tundra and wet sedge meadow tundra (Viereck et al. 1992). The drier sites and low uplands support dwarf scrub dominated by various ericaceous shrubs and dwarf willow. On shallow, rocky soils and exposed sites, lichens and scattered herbs dominate the ground layer. Flood plains support a mixture of low willow scrub and scattered herbs. Fire is not common in this MLRA (AICC 2022).

LRU notes

The bulk of the MLRA is associated with the Circumpolar Arctic Vegetation Mapping (CAVM) subzone D with a small portion of the Northern most lands falling into subzone C (CAVM 2022). Arctic subzone D is associated with vegetation that have herbaceous and dwarf shrub communities that are commonly 4 to 15 inches tall, while subzone C has an herbaceous and dwarf shrub layer that are typically less than 6 inches tall (CAVM 2022). At this time, these differences in community structure are recognized with large differences in annual production expected; but unique ecological sites for each CAVM bioclimate subzone were not developed.

Classification relationships

Landfire BPS – 17080 – Alaska Arctic Polygonal Ground Shrub-Tussock Tundra
(Landfire 2009)

Ecological site concept

-Associated with high-centered ice-wedge polygons on the slopes of plains. The reference state is a complex of two ecological sites related to microtopography: trough and the interior- or domed-center. An alternate thermokarst state indicates how this complex changes with ice-wedge degradation.
-Soils formed in organic material and sandy and silty eolian deposits that are cryoturbated.
- Permafrost occurs at shallow and moderate depth.
-The ice-wedge troughs pond frequently for very long durations of time and are considered very poorly drained. Soils have deep and thick glacic horizons often composed of pure ice.
-Thermokarst of ice-wedges causing improved drainage on the domed centers of polygons. Domed centers in the reference state pond occasionally and are considered poorly drained, while domed centers in the alternate state no longer pond and are considered poorly and somewhat poorly drained. Improved soil drainage significantly decreases tussock cover and increases dwarf scrub cover.
-The reference plant community for domed centers is mixed shrub tussock tundra (Viereck et al. 1992) with tealeaf willow, dwarf birch, lingonberry, and tussock cottongrass common plants. The reference plant community for troughs is wet sedge meadow tundra (Viereck et al. 1992) with tall cottongrass, water sedge, and Sphagnum moss common plants.

Associated sites

R246XY004AK	Arctic Shrub Sandy Flood Plains Occurs downslope on flood plains and incised drainageways that support open and closed willow thickets.
R246XY005AK	Arctic Ice-Wedge Polygon Complex Occurs downslope on stream terraces and drained lake basins with low- and high-center ice-wedge polygons.
R246XY008AK	Arctic Sedge Peat Frozen Drainageways Occurs downslope in low-gradient drainageways with wet sedge meadow tundra.
R246XY012AK	Arctic Dwarf Scrub Sandy Coastal Plain Occurs upslope on inland dunes with dwarf scrub vegetation.
R246XY014AK	Arctic Sedge Peat Frozen Depressions Occurs downslope in depressions without ice-wedge polygons. Associated with wet sedge meadow tundra.

Similar sites

R246XY005AK	Arctic Ice-Wedge Polygon Complex Ecological site complex 005 and 009 model soils and vegetation associated with ice-wedge polygons. Ecological site complex 005 describes landforms with both low-center and high-center polygons, which differs from this ecological site complex.

R246XY005AK

Arctic Ice-Wedge Polygon Complex

Ecological site complex 005 and 009 model soils and vegetation associated with ice-wedge polygons. Ecological site complex 005 describes landforms with both low-center and high-center polygons, which differs from this ecological site complex.

Figure 1. A drained lake with both low- and high-center polygons associated with ecological site complex 005.

Table 1. Dominant plant species

Tree	Not specified
Shrub	(1) Salix pulchra (2) Betula nana
Herbaceous	(1) Eriophorum vaginatum

Download full description

Physiographic features

-Associated with landforms that only have high-center ice-wedge polygons. In the National Petroleum Reserve, common landforms include slopes of the coastal plain. These polygons have two microtopographic positions being the ice wedge trough and the interior or domed center.
-Occurs on nearly level and gentle slopes of plains. Given the low relief, aspect is not relevant for this ecological site concept.
-Elevation occurs between 10 and 330 feet.
-Soils do not flood.
-Ice wedge troughs pond frequently for very long durations. A water table occurs at the soil surface throughout the growing season.

Reference State
-Associated with low-relief high-center polygons.
-Troughs are generally less than 3 feet wide and have 2 to 8 inches of ponded water throughout much of the growing season.
-Minimal relief exists between the troughs and domed center of polygons (ie less than 3 feet).
-The interior or domed centers of polygons pond occasionally for brief durations. A water table occurs at very shallow depth throughout the growing season.

Thermokarst State
-Associated with high-relief, high-center polygons.
-Troughs are greater than 3 feet wide and have 12 to 24 inches or more ponded water.
-Substantial relief exists between the troughs and domed center of polygons (ie between 3 and 10 or more feet).
-The interior or domed centers of polygons do not pond. As relief increases, permafrost thaws to deeper depths and soils have improved drainage. During the growing season, a water table ranges between very shallow and shallow depth.

Figure 2. Satellite image of low-relief, high-center polygons adjacent to sand dunes on the Arctic Coastal Plain.

Figure 3. Satellite image of high-relief, high-center polygons with extensive pools of water in ice wedge trough.

Table 2. Representative physiographic features

Landforms	(1) Coastal plain > Plain (2) Coastal plain > Plain (3) Coastal plain > Patterned ground > Ice wedge polygon (4) Coastal plain > Patterned ground > High-center polygon
Runoff class	Negligible to very low
Flooding frequency	None
Ponding duration	Brief (2 to 7 days) to long (7 to 30 days)
Ponding frequency	Occasional to frequent
Elevation	10 – 330 ft
Slope	4%
Ponding depth	2 – 8 in
Water table depth	10 in
Aspect	Aspect is not a significant factor

Table 3. Representative physiographic features (actual ranges)

Runoff class	Not specified
Flooding frequency	Not specified
Ponding duration	Very long (more than 30 days)
Ponding frequency	None to frequent
Elevation	10 – 820 ft
Slope	Not specified
Ponding depth	24 in
Water table depth	30 in

Climatic features

Very short, cool summers and long, cold winters characterize the arctic climate associated with this ecological site. Given its far North latitude, this Arctic Coastal Plains MLRA experiences long-periods of continuous light in the summer (85 days in Utqiagvik) and continuous darkness in the winter (65 days in Utqiagvik). Mean annual temperature for the Arctic Coastal Plains MLRA typically ranges from 11 to 14 degrees Fahrenheit. The warmest months span June through August with mean normal temperatures ranging from 40 to 47 degrees Fahrenheit (PRISM 2008). The coldest months span December through March with mean normal temperatures ranging from -19 to -9 degrees Fahrenheit (PRISM 2008). This MLRA is arid with mean annual precipitation ranging from 4 to 8 inches. Approximately half of the annual precipitation occurs during the months of July through September. The average annual snowfall ranges from 20 to 40 inches (USDA 2022). The ground is consistently covered with snow from October through May March.

Table 4. Representative climatic features

Frost-free period (characteristic range)	10-28 days
Freeze-free period (characteristic range)	43-76 days
Precipitation total (characteristic range)	4-8 in
Frost-free period (actual range)	3-48 days
Freeze-free period (actual range)	23-94 days
Precipitation total (actual range)	3-9 in
Frost-free period (average)	17 days
Freeze-free period (average)	61 days
Precipitation total (average)	6 in

Characteristic range

Actual range

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Figure 4. Monthly precipitation range

Characteristic range

Actual range

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Figure 5. Monthly minimum temperature range

Characteristic range

Actual range

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Figure 6. Monthly maximum temperature range

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Figure 7. Monthly average minimum and maximum temperature

Figure 8. Annual precipitation pattern

Figure 9. Annual average temperature pattern

Climate stations used

(1) BARROW POST ROGERS AP [USW00027502], Barrow, AK
(2) KUPARUK [USC00505136], Prudhoe Bay, AK
(3) PRUDHOE BAY [USC00507780], Prudhoe Bay, AK

Influencing water features

Precipitation and ground water are the main sources of water (Smith et al. 1995).
Depth to the water table may decrease following summer storm events or spring snowmelt and increase during extended dry periods.

Wetland description

This site is classified as a slope wetland under the Hydrogeomorphic (HGM) classification system (Smith et al. 1995; USDA-NRCS 2008).

Soil features

-Soils formed in organic material and eolian deposits that are cryoturbated.
-Rock fragments do not occur on the soil surface or in the soil profile.
-Soils are capped with 8 inches or more peat and mucky peat that varies with cryoturbation and polygon microtopographic position. The surface mineral horizon textures are fine sand and highly organic silt loam.
-The ice-wedge troughs have glacic horizons that are often pure ice. During field work in the National Petroleum Reserve, these troughs were cored, and the ice-wedges extend to depths beyond 60 inches.
- While soils are considered very deep, permafrost is a restriction that occurs at shallow and moderate depth (12 and 32 inches).
-The pH of the soil profile ranges from very strongly acidic to slightly acidic.
-Ice-wedge troughs are considered very poorly drained.

Reference State
-The ice-wedge troughs are capped with 8 or more inches of peat and mucky peat.
-The interior or domed centers of polygons are considered poorly drained.

Thermokarst State
-The troughs in the thermokarst state had thicker organic caps, which were commonly 15 or more inches thick and composed of peat and mucky peat.
- Permafrost in domed centers thaws and goes deeper in the soil profile resulting in soils that are considered poorly and somewhat poorly drained.

This Arctic High-Center Polygon ecological site complex is correlated to five soil components: Anajuk, Inigok, Pingok, and E46-Arctic scrub-organic frozen high-center polygons. All soils classified as Gelisols. Anajuk occurs in the troughs of low-relief high-center polygons and classifies in the subgroup Glacic Histoturbels; Inigok occurs on the domes of low-relief high-center polygons and is Typic Histoturbels; Pingok occurs in the troughs of high-relief high-center polygons and is Hemic Glacistels. During field work in the National Petroleum Reserve, high-relief high-center polygons were associated with both Inigok and Bansheecreek soils, which depends on the amount of thermokarst and relief. Bansheecreek classifies as Typic Folistels.

Figure 10. Frost crack intersection in arctic soils (in Kerfoot 1972).

Figure 11. Ice-wedges extend to depths beyond 60 inches.

Figure 12. Photo of a Inigok soil sampled on the dome of a low-relief, high-center polygon in the National Petroleum Reserve-Beaufort Coastal Plain soil survey.

Figure 13. Photo of a Anajuk soil sampled in the trough of a low-relief, high-center polygon in the National Petroleum Reserve-Beaufort Coastal Plain soil survey.

Figure 14. Photo of a Pingok soil sampled in the trough of high-relief, high-center polygon in the National Petroleum Reserve-Beaufort Coastal Plain soil survey.

Figure 15. Photo of a Bansheecreek soil sampled on the dome of a high-relief, high-center polygon in the National Petroleum Reserve-Beaufort Coastal Plain soil survey.

Table 5. Representative soil features

Parent material	(1) Organic material (2) Eolian deposits
Surface texture	(1) Peat (2) Mucky peat (3) Permanently frozen fine sand (4) Permanently frozen, highly organic silt loam
Family particle size	(1) Sandy (2) Loamy
Drainage class	Very poorly drained to poorly drained
Permeability class	Moderately rapid
Depth to restrictive layer	12 – 32 in
Soil depth	60 in
Surface fragment cover <=3"	Not specified
Surface fragment cover >3"	Not specified
Available water capacity (0-40in)	2.4 – 8.7 in
Calcium carbonate equivalent (10-40in)	Not specified
Clay content (0-20in)	5%
Electrical conductivity (10-40in)	1 mmhos/cm
Sodium adsorption ratio (10-40in)	1
Soil reaction (1:1 water) (10-40in)	4.5 – 6.5
Subsurface fragment volume <=3" (0-60in)	Not specified
Subsurface fragment volume >3" (0-60in)	Not specified

Table 6. Representative soil features (actual values)

Drainage class	Very poorly drained to somewhat poorly drained
Permeability class	Very slow to rapid
Depth to restrictive layer	7 – 39 in
Soil depth	Not specified
Surface fragment cover <=3"	Not specified
Surface fragment cover >3"	Not specified
Available water capacity (0-40in)	2.4 – 11 in
Calcium carbonate equivalent (10-40in)	Not specified
Clay content (0-20in)	Not specified
Electrical conductivity (10-40in)	Not specified
Sodium adsorption ratio (10-40in)	3
Soil reaction (1:1 water) (10-40in)	3.6 – 7.8
Subsurface fragment volume <=3" (0-60in)	Not specified
Subsurface fragment volume >3" (0-60in)	Not specified

Ecological dynamics

Ecological Site Complex

The two plant communities in the reference and thermokarst state represent the distinct microtopographic positions of high-center ice-wedge polygon. Each microtopographic position represents a unique ecological site that was combined into a complex. The soils and vegetation are linked together through the formation and deterioration of the ice-wedges, which create vegetation shifts across a landform. The significant shifts in vegetation occur in a patchwork and is best illustrated with an ecological site complex.

Ice-wedge polygons genesis and transitions

The soils in the arctic reach extremely cold temperatures resulting in thermal contraction and ground cracking. During the winters of 1949 and 1950 in Utqiagvik, soil temperatures ranged between -13 to 5 degrees Fahrenheit, which would cause a 65-foot block of soil to contract ~0.75 inches (Black 1952). Soil contraction at extremely cold temperature results in incredible stress that is relieved through cracking of the soil profile. At first, the ground cracks in a random pattern (Kerfoot 1972). In subsequent winters, secondary cracks typically occur at orthogonal angels which eventually lead to a field of patterned, polygonal ground (Lachenbruch 1962; Kerfoot 1972). The first polygons on the ground are large (35 to 325 feet) but subsequent soil cracking can result in smaller polygonal divisions (15 to 25 feet) (Black 1952).

During spring snowmelt, these soil cracks fill with water that immediately freeze marking the start of an ice wedge. This ongoing process results in the growth of ice wedges. As the ground warms each summer, the ice wedges are comparatively more rigid than the surrounding soils. The ice wedge block is heaved upward and/or the adjacent soils move along the side of the ice (Leffingwell 1915); either action results in a bulge in the once flat ground. After centuries of continued ice wedge growth, low-center polygon are expressed on the landscape. A well-developed low-center polygon has a center that is depressed relative to its boundary. Low-center, ice-wedge polygons have three distinct microtopographic positions: ice-wedge trough, adjacent rim, and the low-center of the polygon. Analyses of the Colville River floodplain indicate that complete development of high-density, low-centered polygons can take 1500–3000 years (Jorgenson et al. 1998).

Low-center polygons transition to high-center polygons over varying timescales. A well expressed high-center polygon has a raised center relative to its boundary and has two distinct microtopographic positions: domed center and ice-wedge trough. The transition from low- to high-center polygon can result from multiple combined processes (Black 1952). First, thermal erosion of the ice wedge can cause the low-center rim to subside or collapse. Second, organic and mineral soil can fill the low-center of polygon, which can occur from vegetative growth, soil creep, and/or windblown soil deposition. Each process ultimately results in the once concave shaped depression now being a flat to convex shaped dome. While the transition from low- to high-center polygons can naturally take thousands of years (Jorgenson et al. 1998), this transition is greatly hastened due to climate change and/or anthropogenic ground disturbances (Billings and Peterson 1980; Jorgenson et al. 2006; Liljedahl et al. 2016).

Landforms and Ice-Wedge Polygons

In the National Petroleum Reserve soil survey, low-center polygon are not common on the slopes of plains. These slopes are stable features having been present since the last Ice Age (Jorgenson and Shur 2007) and have long ago transitioned to high-center polygon. Landforms with only high-center polygons are associated with this Arctic High-Center Polygon Complex. Landforms like stream terraces and drained lake basins commonly have both low- and high-center polygons. These landforms have soils and vegetation that will have different responses to disturbance and are associated with the Arctic Ice-Wedge Polygon Complex.

Thermokarst of high-center polygons

Increases in temperature are degrading the ice wedges of high-center polygon across the Arctic Coastal Plain MLRA (Jorgenson et al. 2006; Liljedhl et al..2016). Thermal erosion of ice wedges leads to ground subsidence and increases in the extent of standing water in ice wedge troughs. In areas without significant subsidence, the dome of the polygon is relatively flat and tussock forming sedges dominate (herein called low-relief, high-center polygons). In areas with significant ice-wedge degradation and subsidence, the dome of the polygon can be several feet higher compared to the trough (herein called high-relief, high-center polygons). As relief increases, ponding on the polygon dome decreases and soils become drier. These changes in hydrology result in the death and decreased cover of tussock forming sedges and increased cover and dominance of dwarf ericaceous shrubs. For the provisional state and transition model, the reference state is associated with low-relief, high-center polygons and the thermokarst state is associated with high-relief, high-center polygons.

State and transition model

More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective text

Ecosystem states

1. Reference State

2. Thermokarst State

T1	-	thermal erosion of ice-wedges

State 1 submodel, plant communities

1.1. tealeaf willow - dwarf birch / tussock cottongrass

1.2. tall cottongrass - water sedge / Sphagnum moss

State 2 submodel, plant communities

2.1. marsh Labrador tea - lingonberry / tussock cottongrass / splendid feathermoss - turgid Aulacomnium moss

2.2. tall cottongrass - water sedge / Sphagnum moss

State 1
Reference State

Figure 16. Aerial image of low-relief, high-center polygons in the National Petroleum Reserve.

This state relates to low-relief, high-center polygons, which are polygon with relatively flat centers that are raised relative to its boundary. There are two associated plant communities related to polygon microtopography in this state: domed center of the polygon (community 1.1) and ice wedge trough (community 1.2). The troughs are perennially ponded with shallow water and support a wet graminoid herbaceous community dominated by various sedges. The polygon dome are dominated by tussock forming sedges. Soils pond briefly after snowmelt.

Dominant plant species

tealeaf willow (Salix pulchra), shrub
dwarf birch (Betula nana), shrub
tussock cottongrass (Eriophorum vaginatum), grass

Community 1.1
tealeaf willow - dwarf birch / tussock cottongrass

Figure 17. Typical vegetation associated with community 1.1.

This community is characterized as tussock tundra or mixed shrub-sedge tussock tundra (Viereck et al. 1992) with the dominant plants being dwarf birch, tealeaf willow, lingonberry, tussock cottongrass, Bigelow's sedge, turgid Aulacomnium moss, Dicranum moss, and splendid feathermoss. The binomial name of these and other less common associated plants can be found in the below dominant plant species table. The vegetative strata that characterize this community are medium graminoids (between 4 and 24 inches), dwarf shrubs (less than 8 inches in height), and moss.

Dominant plant species

lingonberry (Vaccinium vitis-idaea), shrub
tealeaf willow (Salix pulchra), shrub
dwarf birch (Betula nana), shrub
white arctic mountain heather (Cassiope tetragona), shrub
marsh Labrador tea (Ledum palustre ssp. decumbens), shrub
netleaf willow (Salix reticulata), shrub
entireleaf mountain-avens (Dryas integrifolia), shrub
tussock cottongrass (Eriophorum vaginatum), grass
Bigelow's sedge (Carex bigelowii), grass
turgid aulacomnium moss (Aulacomnium turgidum), other herbaceous
splendid feather moss (Hylocomium splendens), other herbaceous
dicranum moss (Dicranum), other herbaceous
(Flavocetraria cucullata), other herbaceous
arctic dactylina lichen (Dactylina arctica), other herbaceous
whiteworm lichen (Thamnolia vermicularis), other herbaceous
greygreen reindeer lichen (Cladina rangiferina), other herbaceous
meadow bistort (Polygonum bistorta), other herbaceous

Community 1.2
tall cottongrass - water sedge / Sphagnum moss

Figure 18. Typical vegetation associated with community 1.2.

Figure 19. Field staff pointing to ice wedge trough.

Community 1.2 is characterized as wet sedge meadow tundra (Viereck et al. 1992) with the dominant plants being tall cottongrass, water sedge, and Sphagnum moss. The binomial name of these and other less common associated plants can be found in the below dominant plant species table. The vegetative strata that characterize this community are medium graminoids (between 4 and 24 inches) and moss. The peaty soils are typically covered with several inches of ponded water.

Dominant plant species

tealeaf willow (Salix pulchra), shrub
marsh Labrador tea (Ledum palustre ssp. decumbens), shrub
lingonberry (Vaccinium vitis-idaea), shrub
tall cottongrass (Eriophorum angustifolium), grass
water sedge (Carex aquatilis), grass
tussock cottongrass (Eriophorum vaginatum), grass
Bigelow's sedge (Carex bigelowii), grass
sphagnum (Sphagnum), other herbaceous
aulacomnium moss (Aulacomnium palustre), other herbaceous

State 2
Thermokarst State

Figure 20. Aerial image of high-relief, high-center polygons in the National Petroleum Reserve. The edges of these polygons have large and connected pools.

This state relates to high-relief, high-center polygons, which are polygon with sloping centers that are often significantly raised relative to its boundary. There are two associated plant communities related to polygon microtopography in this state: domed center of the polygon (community 1.1) and ice wedge trough (community 1.2). The troughs are often perennially ponded with shallow water and supports a wet graminoid herbaceous community dominated by various sedges. The polygon dome is dominated by dwarf scrubs, sedges, and various moss. Due to changes in hydrology, tussocks are commonly dead or dying.

Dominant plant species

marsh Labrador tea (Ledum palustre ssp. decumbens), shrub
lingonberry (Vaccinium vitis-idaea), shrub
tussock cottongrass (Eriophorum vaginatum), grass
splendid feather moss (Hylocomium splendens), other herbaceous
turgid aulacomnium moss (Aulacomnium turgidum), other herbaceous

Community 2.1
marsh Labrador tea - lingonberry / tussock cottongrass / splendid feathermoss - turgid Aulacomnium moss

Figure 21. Typical vegetation associated with community 2.1.

Figure 22. Withered and dying tussocks are common.

Community 2.1 is characterized as ericaceous dwarf scrub tundra (Viereck et al. 1992) with the dominant plants being marsh Labrador tea, lingonberry, tussock cottongrass, and various moss. While tussocks are present, tussocks commonly appear withered and/or dead. The binomial name of these and other less common associated plants can be found in the below dominant plant species table. The strata that characterize this community are dwarf scrub (less than 8 inches tall) and to a much less extent medium graminoids (between 4 and 24 inches tall) and moss.

Dominant plant species

lingonberry (Vaccinium vitis-idaea), shrub
marsh Labrador tea (Ledum palustre ssp. decumbens), shrub
dwarf birch (Betula nana), shrub
entireleaf mountain-avens (Dryas integrifolia), shrub
white arctic mountain heather (Cassiope tetragona), shrub
netleaf willow (Salix reticulata), shrub
black crowberry (Empetrum nigrum), shrub
tealeaf willow (Salix pulchra), shrub
alpine bearberry (Arctostaphylos alpina), shrub
tussock cottongrass (Eriophorum vaginatum), grass
Bigelow's sedge (Carex bigelowii), grass
alpine sweetgrass (Anthoxanthum monticola ssp. alpinum), grass
wideleaf polargrass (Arctagrostis latifolia), grass
turgid aulacomnium moss (Aulacomnium turgidum), other herbaceous
splendid feather moss (Hylocomium splendens), other herbaceous
dicranum moss (Dicranum), other herbaceous
meadow bistort (Polygonum bistorta), other herbaceous
juniper polytrichum moss (Polytrichum juniperinum), other herbaceous
narrowleaf saw-wort (Saussurea angustifolia), other herbaceous

Community 2.2
tall cottongrass - water sedge / Sphagnum moss

Figure 23. Large pools of water in an ice wedge trough associated with community 2.2.

Community 2.2 is characterized as wet sedge meadow tundra (Viereck et al. 1992) with the dominant plants being tall cottongrass, water sedge, and Sphagnum moss. The binomial name of these and other less common associated plants can be found in the below dominant plant species table. The vegetative strata that characterize this plant community are medium graminoids (between 4 and 24 inches in height). The peaty soils are typically covered with several inches of ponded water.

Dominant plant species

tealeaf willow (Salix pulchra), shrub
lingonberry (Vaccinium vitis-idaea), shrub
water sedge (Carex aquatilis), grass
tall cottongrass (Eriophorum angustifolium), grass
round sedge (Carex rotundata), grass
sphagnum (Sphagnum), other herbaceous

Transition T1
State 1 to 2

Reference State

Thermokarst State

Increased soil temperatures lead to the degradation of ice wedges associated with high-center polygon. As ground subsidence increases, ice wedge trough have increased amounts of water and the dome of high-center polygon have decreased ponding frequency and drier soils. This is a process that naturally occurs over hundreds or thousands of years. Anthropogenic disturbance to the soils can rapidly trigger this transition.

Additional community tables

Interpretations

Animal community

Not available

Hydrological functions

Not available

Recreational uses

Not available

Wood products

Not available

Other information

Not available

Supporting information

Inventory data references

The vegetation modeled for this site has limited data coverage across the MLRA and is considered provisional. The associated model was largely developed from literature review, NRCS staff with working knowledge of the area, and sample plots from the National Petroleum Reserve – Beaufort Coastal Plain soil survey (AK760). Tier 2 sampling plots used to develop the reference state are below:

Tier 2 sampling plots used to develop the grazing state. Plot numbers as recorded in NASIS with associated community phase.

Community 1.1

2021AK185001, 2021AK185100, 2021AK185301, 2021AK185307, 2021AK185310, 2021AK185695, 2023AK185101, 2023AK185104, 2023AK185113, 2023AK185116, 2023AK185121, 2023AK185402, 2023AK185407, 2023AK185417, 2023AK185432, 2023AK185800, 2023AK185807, 2023AK185817, S2021AK185131

Community 1.2

2021AK185103, 2021AK185127, 2021AK185711, 2021AK185713, 2023AK185403, 2023AK185408, 2023AK185801

Community 2.1

2021AK185706, 2023AK185112, 2023AK185128, 2023AK185129, 2023AK185412, 2023AK185421, 2023AK185433, 2023AK185805, 2023AK185810, 2023AK185811

Community 2.2

2021AK185693, 2023AK185413

References

Viereck, L.A., C. T. Dyrness, A. R. Batten, and K. J. Wenzlick. 1992. The Alaska vegetation classification. U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station General Technical Report PNW-GTR-286..

Other references

Billings W. D., and Peterson K.M. 1980. Vegetational change and ice wedge polygons through the thaw lake cycle in Arctic Alaska, Arct. Alp. Res., 12, 413– 432.

Black R.F. 1952. Polygonal patterns and ground conditions from aerial photographs.
Photogrammetric Engineering, 18: 123-34.

CAVM Team. 2003. Circumpolar Arctic Vegetation Map. (1:7,500,000 scale), Conservation of Arctic Flora and Fauna (CAFF) Map No. 1. U.S. Fish and Wildlife Service, Anchorage, Alaska.

Lachenbruch A.H. 1962. Mechanics of thermal contraction cracks and ice-wedge polygons in permafrost. Geological Society of America, Special Paper, 70: 69 pp.

LANDFIRE. 2009. LANDFIRE National Vegetation Dynamics Models. USDA Forest Service and US Department of Interior. Washington, DC.

Leffingwell E.K. 1915. Ground Ice-Wedges. The dominant form of ground ice on the north coast of Alaska. Journal of Geology, 23: 635-54.

Liljedahl, A. K. et al. 2016. Pan-Arctic ice-wedge degradation in warming permafrost and its influence on tundra hydrology. Nat. Geosci. 9, 312–318.

Jorgenson M.T., Shur Y., and Walker H.J. 1998., Factors affecting evolution of a permafrost-dominated landscape on the Colville River Delta, northern Alaska, Collect. Nord., 57, 523–530.

Jorgenson M.T., Shur Y., and Pullman E.R. 2006. Abrupt increase in permafrost
degradation in Arctic Alaska. Geophys. Res. Lett. 33, L02503.

Jorgenson M.T, and Shur Y. 2007. Evolution of lakes and basins in northern Alaska and discussion of the thaw lake cycle J. Geophys. Res., 112 (F2).

Kerfoot, D. E. 1972. Thermal contraction cracks in an arctic tundra environment, Arctic, 25, 142–150.

Contributors

Blaine Spellman
Gabriel Benitez
Tyler Annetts

Approval

Blaine Spellman, 5/22/2025

Acknowledgments

Marji Patz provided quality control review of these provisional ecological sites.

Rangeland health reference sheet

Interpreting Indicators of Rangeland Health is a qualitative assessment protocol used to determine ecosystem condition based on benchmark characteristics described in the Reference Sheet. A suite of 17 (or more) indicators are typically considered in an assessment. The ecological site(s) representative of an assessment location must be known prior to applying the protocol and must be verified based on soils and climate. Current plant community cannot be used to identify the ecological site.

Author(s)/participant(s)
Contact for lead author
Date	05/26/2025
Approved by	Blaine Spellman
Approval date
Composition (Indicators 10 and 12) based on	Annual Production

Indicators

Number and extent of rills:
Presence of water flow patterns:
Number and height of erosional pedestals or terracettes:
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Number of gullies and erosion associated with gullies:
Extent of wind scoured, blowouts and/or depositional areas:
Amount of litter movement (describe size and distance expected to travel):
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
Functional/Structural Groups (list in order of descending dominance by above-ground annual-production or live foliar cover using symbols: >>, >, = to indicate much greater than, greater than, and equal to):

Dominant:

Sub-dominant:

Other:

Additional:
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
Average percent litter cover (%) and depth ( in):
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
Potential invasive (including noxious) species (native and non-native). List species which BOTH characterize degraded states and have the potential to become a dominant or co-dominant species on the ecological site if their future establishment and growth is not actively controlled by management interventions. Species that become dominant for only one to several years (e.g., short-term response to drought or wildfire) are not invasive plants. Note that unlike other indicators, we are describing what is NOT expected in the reference state for the ecological site:
Perennial plant reproductive capability: