Natural Resources
Conservation Service

Ecological site R236XY132AK

Subarctic Dwarf Scrub Dry Loamy Slopes

Last updated: 2/13/2024
Accessed: 09/24/2026

Home / esd CATALOG / MLRA 236X / ecological site R236XY132AK

USC

Metric

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): 236X–Bristol Bay-Northern Alaska Peninsula Lowlands

The Bristol Bay-Northern Alaska Peninsula Lowland Major Land Resource Area (MLRA 236) is located in Western Alaska. This MLRA covers approximately 19,500 square miles and is defined by an expanse of nearly level to rolling lowlands, uplands and low to moderate hills bordered by long, mountain footslopes. Major rivers include the Egegik, Mulchatna, Naknek, Nushagak, and Wood River. MLRA 236 is in the zone of discontinuous permafrost. It is primarily in areas with finer textured soils on terraces, rolling uplands and footslopes. This MLRA was glaciated during the early to middle Pleistocene. Moraine and glaciofluvial deposits cover around sixty percent of the MLRA. Alluvium and coastal deposits make up a large portion of the remaining area (Kautz et al., 2012; USDA, 2006).

Climate patterns across this MLRA shift as one moves away from the coast. A maritime climate is prominent along the coast, while continental weather, commonly associated with Interior Alaska, is more influential inland. Across the MLRA, summers are general short and warm while winters are long and cold. Mean annual precipitation is 13 to 50 inches, with increased precipitation at higher elevations and areas away from the coast. Mean annual temperatures is between 30 and 36 degrees F (USDA, 2006).

The Bristol Bay-Northern Alaska Peninsula MLRA is principally undeveloped wilderness. Federally managed land includes parts of the Katmai and Aniakchak National Parks, and the Alaska Peninsula, Becharof, Togiak and Alaska Maritime National Wildlife Refuges. The MLRA is sparsely populated. Principal communities include Dillingham, Naknek, and King Salmon. Commercial fishing in Bristol Bay and the Bering Sea comprises a major part of economic activity in the MLRA. Other land uses include subsistence activities (fishing, hunting, and gathering) and sport hunting and fishing (USDA, 2006).

Classification relationships

Alaska Vegetation Classification:
Open low scrubland (II.C.2 - level III) / Open low mesic shrub birch-ericaceous shrubland (II.C.2.c - level IV)
(Viereck et al., 1992)

Ecological site concept

This ecological site is on linear to convex shoulders of hills and rolling glaciated plains. Site elevation is between 160 and 970 feet above sea level. Slopes are nearly level to strongly sloped. Site wind exposure, low water availability, limited soil development, and natural wildlife grazing pressure shape the vegetation on this landform.

The reference state supports three communities. The reference plant community is characterized as an open, low mesic scrubland (Viereck et al., 1992). It is composed of a mix of ericaceous and non-ericaceous shrubs with lichen throughout. The other communities on this site are a post-grazed community and a highly eroded community.

Associated sites

R236XY130AK	Subarctic Scrub Scrub Tundra Loamy Plains and Hills Both sites are on plains. R236XY130AK describes open, low scrublands on toeslopes. R236XY132AK describes a scrubland on exposed, convex rolling plain and hill shoulders.
R236XY131AK	Subarctic Tussock-Scrub Frozen Plains Both sites are on plains. R236XY132AK is primarily associated with shoulders of rolling plains and hills. R236XY131AK describes a tussock tundra community in concave areas of plain slopes.
R236XY140AK	Subarctic Tussock Tundra Wet Loamy Plains Both sites are on plain landscapes. R236XY140AK is on linear plain talfs, while R236XY132AK is on upslope, convex shoulders of rolling plains. Soils in R236XY140AK are comprised of organic material over loamy eolian deposits. This soil is poorly drained with frequent, brief ponding during the growing season. Soils in R236XY132AK are well drained and do not support the hydrophytic communities of R236XY140AK.

R236XY130AK

Subarctic Scrub Scrub Tundra Loamy Plains and Hills

Both sites are on plains. R236XY130AK describes open, low scrublands on toeslopes. R236XY132AK describes a scrubland on exposed, convex rolling plain and hill shoulders.

R236XY131AK

Subarctic Tussock-Scrub Frozen Plains

Both sites are on plains. R236XY132AK is primarily associated with shoulders of rolling plains and hills. R236XY131AK describes a tussock tundra community in concave areas of plain slopes.

R236XY140AK

Subarctic Tussock Tundra Wet Loamy Plains

Both sites are on plain landscapes. R236XY140AK is on linear plain talfs, while R236XY132AK is on upslope, convex shoulders of rolling plains. Soils in R236XY140AK are comprised of organic material over loamy eolian deposits. This soil is poorly drained with frequent, brief ponding during the growing season. Soils in R236XY132AK are well drained and do not support the hydrophytic communities of R236XY140AK.

Similar sites

R236XY130AK	Subarctic Scrub Scrub Tundra Loamy Plains and Hills Both sites are on plains. R236XY130AK describes open, low scrublands on toeslopes. Soil is wetter in these positions than on the convex shoulder positions described by R236XY132AK. There is vegetative overlap in the species found in these sites but the community composition and community phases are different.
R236XY131AK	Subarctic Tussock-Scrub Frozen Plains Both sites are on plains. R236XY132AK is primarily associated with shoulders of rolling plains and hills. R236XY131AK describes a tussock tundra community on organic permafrost soils in concave areas. The soil hydrology in concave areas, along with frost heave due to underlying permafrost, are distinctly different than the well drained soils and corresponding vegetation of convex plain slopes.

R236XY130AK

Subarctic Scrub Scrub Tundra Loamy Plains and Hills

Both sites are on plains. R236XY130AK describes open, low scrublands on toeslopes. Soil is wetter in these positions than on the convex shoulder positions described by R236XY132AK. There is vegetative overlap in the species found in these sites but the community composition and community phases are different.

R236XY131AK

Subarctic Tussock-Scrub Frozen Plains

Both sites are on plains. R236XY132AK is primarily associated with shoulders of rolling plains and hills. R236XY131AK describes a tussock tundra community on organic permafrost soils in concave areas. The soil hydrology in concave areas, along with frost heave due to underlying permafrost, are distinctly different than the well drained soils and corresponding vegetation of convex plain slopes.

Table 1. Dominant plant species

Tree	Not specified
Shrub	(1) Betula nana (2) Ledum palustre subsp. decumbens
Herbaceous	(1) Carex bigelowii

Download full description

Physiographic features

This site is on linear to convex shoulders of hills and rolling glaciated plains. Elevation ranges from 160 to 970 feet above sea level. Slopes are nearly level to strongly slopes (1 – 10 percent). This site is found at all aspects. Neither flooding nor ponding occur.

Table 2. Representative physiographic features

Slope shape across	(1) Linear
Slope shape up-down	(1) Convex
Geomorphic position, flats	(1) Talf (2) Rise
Hillslope profile	(1) Shoulder
Landforms	(1) Plains > Plain (2) Hills > Hill
Runoff class	Negligible to medium
Flooding frequency	None
Ponding frequency	None
Elevation	160 – 970 ft
Slope	1 – 10 %
Water table depth	60 – 0 in
Aspect	W, NW, N, NE, E, SE, S, SW

Table 3. Representative physiographic features (actual ranges)

Runoff class	Negligible to medium
Flooding frequency	None
Ponding frequency	None
Elevation	0 – 2050 ft
Slope	0 – 20 %
Water table depth	60 – 0 in

Climatic features

The climate of this site reflects that of the MLRA, which is described as maritime polar (EPA, 2013). Temperatures are moderated by the nearby Bristol Bay and norther Pacific bodies of water. Annual precipitation ranges from 21 – 34 inches with approximately 40 percent occurring during the June-September growing season (PRISM, 2018).

Table 4 Representative climatic features

Frost-free period (characteristic range)	80-100 days
Freeze-free period (characteristic range)	70-90 days
Precipitation total (characteristic range)	20-30 in
Frost-free period (actual range)	80-100 days
Freeze-free period (actual range)	70-90 days
Precipitation total (actual range)	20-40 in
Frost-free period (average)	90 days
Freeze-free period (average)	80 days
Precipitation total (average)	30 in

Characteristic range

Actual range

Bar

Line

Figure 1. Monthly precipitation range

Characteristic range

Actual range

Bar

Line

Figure 2. Monthly minimum temperature range

Characteristic range

Actual range

Bar

Line

Figure 3. Monthly maximum temperature range

Bar

Line

Figure 4. Monthly average minimum and maximum temperature

Figure 5. Annual precipitation pattern

Figure 6 Annual average temperature pattern

Soil features

Soils are young and weakly developed Inceptisols (Soil Survey Staff, 2013). They are very deep and well drained. They support a cryic temperature regime and an udic moisture regime. Parent material is primarily eolian deposits over drift or till.

Vegetation is restricted by water availability and minimal soil development. Available water capacity is very low, particularly in the top ten inches of soil. Subsurface rock fragments contribute to increased water drainage. The minimally developed soil is exemplified by an ochric epipedon above a cambic horizon. Poor soil development mixed with exposed scouring restricts vegetation to primarily prostrate shrubs.

Correlated soil components in MLRA 236:
D36-Western maritime dwarf scrub gravelly glaciated slopes
D36-Western maritime dwarf scrub loamy glaciated slopes
D36-Western maritime dwarf scrub loamy eolian slopes
Stuyahok
E36-Maritime dwarf scrub-gravelly till slopes
E36-Maritime scrub-gravelly colluvial slopes

Table 5. Representative soil features

Parent material	(1) Eolian deposits (2) Drift
Surface texture	(1) Silt (2) Silt loam (3) Highly organic silt loam
Drainage class	Well drained
Permeability class	Moderate
Soil depth	60 – 0 in
Surface fragment cover <=3"	0 – 10 %
Surface fragment cover >3"	Not specified
Available water capacity (0-10in)	1.8 – 2.4 in
Soil reaction (1:1 water) (0-10in)	4.5 – 6
Subsurface fragment volume <=3" (Depth not specified)	0 – 64 %
Subsurface fragment volume >3" (Depth not specified)	Not specified

Table 6. Representative soil features (actual values)

Drainage class	Well drained
Permeability class	Moderate
Soil depth	60 – 0 in
Surface fragment cover <=3"	0 – 10 %
Surface fragment cover >3"	0 %
Available water capacity (0-10in)	0.5 – 2.6 in
Soil reaction (1:1 water) (0-10in)	3.3 – 6.2
Subsurface fragment volume <=3" (Depth not specified)	0 – 64 %
Subsurface fragment volume >3" (Depth not specified)	0 %

Ecological dynamics

This site is on linear to convex shoulders of hills and rolling glaciated plains. Local site factors, including exposure, minimal soil development, and grazing pressures create three distinct communities on this site. The reference plant community is an open, low mesic scrubland comprised of mixed ericaceous and non-ericaceous shrubs.

Grazing is the major disturbance on this site. It is a natural disturbance and is typically unmanaged. Moderate to severe grazing by caribou on lichen decreases lichen community richness and biomass. Decreased lichen reduces competition for light and space, allowing forbs, graminoids, and extant shrubs to spread.

In rare instances, these exposed, convex areas are overgrazed and are eroded by high winds that scour and remove vegetation and soil. These areas are referred to as blowouts. Blowouts are comprised of large areas distinguished by bare soil and surface rock fragments (Sonnen, 2014). Further fieldwork is needed to investigate this disturbance on this site.

The information in this Ecological Dynamics section, including the state-and-transition model (STM), was developed based on current field data, professional experience, and a review of the scientific literature. As a result, all possible scenarios or plant species may not be included. Key indicator plant species, disturbances, and ecological processes are described to inform land management decisions.

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

State 1 submodel, plant communities

1.1. Dwarf birch-marsh Labrador tea

1.2. Marsh Labrador tea-black crowberry

1.3. Black crowberry/Bigelow's sedge

1.1A	-	Grazing.
1.1B	-	Overgrazing and wind erosion.
1.2A	-	Decreased grazing pressure.
1.3A	-	Overgrazing and erosion recovery.

State 1
Reference State

The reference state supports three community phases, which are distinguished by the developed structure and dominance of the vegetation and by their ecological function and stability. The reference community phase is scrubland. The presence of each community is dictated temporally by a disturbance regime of grazing and wind erosion.

This report provides baseline inventory data for the vegetation in this ecological site. Future data collection is needed to provide further information about existing plant communities and the disturbance regime that results in transitions from one community to another. Common and scientific names are from the USDA PLANTS database. Community phases are characterized by the Alaska Vegetation Classification System (Viereck et al., 1992).

Community 1.1
Dwarf birch-marsh Labrador tea

Figure 7. Typical area of community 1.1.

Figure 8. Frequency and canopy cover of plants in community 1.1.

The reference plant community is open low scrubland (Viereck et al., 1992) that consists of low and dwarf shrubs with various dense lichens throughout. This community supports dwarf birch (Betula nana), marsh Labrador tea (Ledum palustre ssp. decumbens), black crowberry (Empetrum nigrum), bog blueberry (Vaccinium uliginosum), and lichens such as cup lichen (Cladonia spp.), reindeer lichen (Cladina spp.), and snow lichen (Stereocaulon spp.). Other species may include lingonberry (Vaccinium vitis-idaea), alpine azalea (Loiseleuria procumbens), alpine bearberry (Arctostaphylos alpina), Bigelow’s sedge (Carex bigelowii), and variegated sedge (Carex stylosa). Individual stunted white spruce (Picea glauca) and quaking aspen (Populus tremuloides) trees may be present, but they are rare. Lichens are the major component of the ground cover. Other ground cover includes herbaceous litter, mosses, rock fragments, and woody litter. Some areas are bare soil.

Dominant plant species

dwarf birch (Betula nana), shrub
marsh Labrador tea (Ledum palustre ssp. decumbens), shrub
black crowberry (Empetrum nigrum), shrub
lingonberry (Vaccinium vitis-idaea), shrub
alpine azalea (Loiseleuria procumbens), shrub
alpine bearberry (Arctostaphylos alpina), shrub
snow lichen (Stereocaulon), other herbaceous
reindeer lichen (Cladina), other herbaceous

Community 1.2
Marsh Labrador tea-black crowberry

Figure 9. Typical area of community 1.2.

Figure 10. Frequency and canopy cover of plants in community 1.2.

The early grazing sere is open low scrubland (Viereck et al., 1992) that consists of low and dwarf shrubs with patches of graminoids and lichens. This community supports marsh Labrador tea, dwarf birch, black crowberry, and lingonberry. Other species commonly interspersed throughout include Bigelow’s sedge, variegated sedge, alpine azalea, and bog blueberry. Lichens and mosses typically are present. The ground cover also commonly includes herbaceous litter, woody litter, and rock fragments. Some areas are bare soil.

Dominant plant species

marsh Labrador tea (Ledum palustre ssp. decumbens), shrub
black crowberry (Empetrum nigrum), shrub
dwarf birch (Betula nana), shrub
lingonberry (Vaccinium vitis-idaea), shrub
bog blueberry (Vaccinium uliginosum), shrub
alpine azalea (Loiseleuria procumbens), shrub
alpine bearberry (Arctostaphylos alpina), shrub
reindeer lichen (Cladina), other herbaceous

Community 1.3
Black crowberry/Bigelow's sedge

Figure 11. Typical area of community 1.3.

Figure 12. Frequency and canopy cover of plants in community 1.3.

This highly disturbed community consists of large areas that have rock fragments on the surface and patches of low and dwarf shrubs. Black crowberry, alpine azalea, marsh Labrador tea, dwarf birch, Bigelow’s sedge, and a small amount of other low and dwarf shrubs may be present. The ground cover includes rock fragments, lichens, mosses, and herbaceous litter. About 9 percent is bare soil.

Dominant plant species

black crowberry (Empetrum nigrum), shrub
marsh Labrador tea (Ledum palustre ssp. decumbens), shrub
dwarf birch (Betula nana), shrub
alpine azalea (Loiseleuria procumbens), shrub
lingonberry (Vaccinium vitis-idaea), shrub
Bigelow's sedge (Carex bigelowii), grass

Pathway 1.1A
Community 1.1 to 1.2

Dwarf birch-marsh Labrador tea

Marsh Labrador tea-black crowberry

Grazing. Grazing of lichen by caribou can create open areas for graminoids and low-lying shrubs to colonize (K. Sonnen, 2014). The period needed for this transition currently is unknown, but it likely is dictated by the intensity and frequency of grazing.

Pathway 1.1B
Community 1.1 to 1.3

Dwarf birch-marsh Labrador tea

Black crowberry/Bigelow's sedge

Overgrazing and wind erosion. Rarely, the community may be susceptible to wind erosion as a result of severe grazing in the exposed convex areas. Scouring of the soil and vegetation by wind may expose surface rock fragments (K. Sonnen, 2014). The period needed for this transition currently is unknown.

Pathway 1.2A
Community 1.2 to 1.1

Marsh Labrador tea-black crowberry

Dwarf birch-marsh Labrador tea

Decreased grazing pressure. Over time, the populations of lichen will increase and the lichen will slowly outcompete shrubs for space (Sonnen, 2014). Based on the known growth rate of lichen, this transition is expected to be very slow.

Pathway 1.3A
Community 1.3 to 1.1

Black crowberry/Bigelow's sedge

Dwarf birch-marsh Labrador tea

For community phase 1.3 to return to the reference community phase, soil formation must be initiated by eolian processes and plant senescence. The colonization and spread of lichens, mosses, graminoids, and forbs may increase as soil formation continues. The period needed for this transition is expected to be very long. It is estimated that 50 to 75 years (Sonnen, 2014) is needed for soil formation to begin, but the period needed for this phase to return to the reference community phase is unknown.

Additional community tables

Table 7. Community 1.1 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 8. Community 1.2 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Table 9. Community 1.3 plant community composition

Group	Common name	Symbol	Scientific name	Annual production ()	Foliar cover (%)

Supporting information

Inventory data references

Modal points for Community 1.1 07MM05201 07MM05303 07MM05305 07SS01805 07SS04502 07AO21701 10SS12102 10SS12401 Modal points for community 1.2 07MM22204 07AO02303 08AO05601 08AO06401 09AO03506 10SS13309 Modal points for community 1.3 07CS00601 09SS13903 10SS08905

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

Kautz, D.R., P. Taber, and S. Nield, editors. 2012. Land Resource Regions and Major Land Resource Areas of Alaska. United States Department of Agriculture, Natural Resources Conservation Service (USDA–NRCS).

PRISM Climate Group. (PRISM) Oregon State University. https://prism.oregonstate.edu. Date created October 2018. Accessed 3 Mar 2023.

Scenarios Network for Alaska and Arctic Planning (SNAP).  Historical Monthly Temperature – 1km, 1901-2009. http://ckan.snap.uaf.edu/dataset/. Accessed 20 Mar 2023.

Scenarios Network for Alaska and Arctic Planning (SNAP).  Historical monthly and derived precipitation products downscaled from CRU TS data via the delta methods – 2km, 1901-2009.  http://ckan.snap.uaf.edu/dataset/. Accessed 20 Mar 2023.

Soil Survey Staff. 2013. Simplified Guide to Soil Taxonomy. USDA-Natural Resources Conservation Service, National Soil Survey Center, Lincoln, NE.

Sonnen, Karin. September 2014. Personal conversation.

United States Department of Agriculture, Natural Resources Conservation Service. 2006. Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook 296.

US Environmental Protection Agency (EPA). Level III Ecoregions of the Conterminous United States. UP ESP Office of Research and Development. Corvallis, OR. http://edg.epa.gov/. Created 16 Apr 2013. Accessed 20 Mar 2023.

Contributors

Phil Barber
Karin Sonnen
Kendra Moseley
Michael Margo
Sue Tester
Steph Schmit
Steff Shoemaker
Jamin Johanson

Approval

Kirt Walstad, 2/13/2024

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	09/24/2026
Approved by
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:

Download reference sheet

Natural ResourcesConservation Service

Ecological site R236XY132AK

Subarctic Dwarf Scrub Dry Loamy Slopes

Last updated: 2/13/2024 Accessed: 09/24/2026

Search

General information

MLRA notes

Classification relationships

Ecological site concept

Associated sites

Similar sites

Table 1. Dominant plant species

Natural Resources
Conservation Service

Last updated: 2/13/2024
Accessed: 09/24/2026