Natural Resources
Conservation Service

Ecological site R236XY173AK

Subarctic Riparian Complex Loamy Flood Plains

Last updated: 2/13/2024
Accessed: 09/23/2026

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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): 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 tall scrubland (II.B.2 - level III) / Willow scrubland (II.B.2.a - level IV)
(Viereck et al., 1992)

Ecological site concept

This ecological site is on convex berm features on flood plains of low energy rivers. Site elevation is between 160 and 980 feet above sea level. Slopes are nearly level (0 – 3 percent). Soil hydrology in the major influencer of vegetation on this site. Soils are somewhat poorly drained. There is a shallow water table during the growing season and non-scouring flooding contributes to water inputs.

The reference state supports one community. The reference plant community is characterized as an open tall scrubland (Viereck et al., 1992). It is composed of one or more willow species with hydrophytic graminoids and forb species throughout. This community is resilient to the hydrologic stressors of this landform position.

Associated sites

R236XY144AK	Subarctic Scrub Peat Terraces R236XY144AK describes terraces that experience ponding disturbances. Terraces are higher in elevation and do not flood like the valley flood plains described by R236XY173AK. Different vegetative communities are supported on these sites due to differences in site and soil characteristics.
F236XY176AK	Boreal Woodland Loamy Flood Plains Both sites are on valley flood plain talfs. F236XY176AK briefly floods and supports a boreal forest community in the reference state. R236XY173AK floods for a long time. This disturbance and site hydrology does not support trees.

R236XY144AK

Subarctic Scrub Peat Terraces

R236XY144AK describes terraces that experience ponding disturbances. Terraces are higher in elevation and do not flood like the valley flood plains described by R236XY173AK. Different vegetative communities are supported on these sites due to differences in site and soil characteristics.

F236XY176AK

Boreal Woodland Loamy Flood Plains

Both sites are on valley flood plain talfs. F236XY176AK briefly floods and supports a boreal forest community in the reference state. R236XY173AK floods for a long time. This disturbance and site hydrology does not support trees.

Similar sites

F236XY176AK	Boreal Woodland Loamy Flood Plains Both sites are on valley flood plain talfs. F236XY176AK supports a forest community in the reference state, which is not present on R236XY173AK. Ecotonal areas exist where trees are present but are not recognized as a forest community.

F236XY176AK

Boreal Woodland Loamy Flood Plains

Both sites are on valley flood plain talfs. F236XY176AK supports a forest community in the reference state, which is not present on R236XY173AK. Ecotonal areas exist where trees are present but are not recognized as a forest community.

Table 1. Dominant plant species

Tree	Not specified
Shrub	(1) Salix pulchra (2) Salix barclayi
Herbaceous	(1) Calamagrostis canadensis (2) Equisetum arvense

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Physiographic features

This site is on flat areas and convex berms along low energy rivers. This site is associated with narrow valley lowland flood plains. Elevation ranges from 160 to 980 feet above sea level. Slopes are nearly level (0 – 3 percent). Flooding is an occasional and long event during the growing season, which limits site plant species. This site is located at all aspects.

Table 2. Representative physiographic features

Slope shape up-down	(1) Linear
Slope shape across	(1) Convex
Geomorphic position, flats	(1) Talf
Landforms	(1) Valley > Flood plain (2) Valley > Flood plain
Runoff class	Negligible to low
Flooding duration	Long (7 to 30 days)
Flooding frequency	Occasional
Ponding frequency	None
Elevation	160 – 980 ft
Slope	0 – 3 %
Water table depth	10 – 20 in
Aspect	W, NW, N, NE, E, SE, S, SW

Table 3. Representative physiographic features (actual ranges)

Runoff class	Negligible to low
Flooding duration	Long (7 to 30 days)
Flooding frequency	Occasional
Ponding frequency	None
Elevation	0 – 1560 ft
Slope	0 – 3 %
Water table depth	7 – 45 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

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Figure 1. Monthly precipitation range

Characteristic range

Actual range

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Figure 2. Monthly minimum temperature range

Characteristic range

Actual range

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Figure 3. Monthly maximum temperature range

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Figure 4. Monthly average minimum and maximum temperature

Figure 5. Annual precipitation pattern

Figure 6 Annual average temperature pattern

Influencing water features

This site is influenced by riparian water features. Occasional, long periods of flooding occur during the early growing season. This disturbance along with negligible to low run off and somewhat poorly drained soils restrict the vegetation on this site. Periods of high precipitation and seasonal ice and snow melt are the main sources of flooding waters.

Soil features

Soils are young and weakly developed Inceptisols (Soil Survey Staff, 2013). Soils are very deep and somewhat poorly drained. They support a cryic temperature regime and an aquic moisture regime. Parent material is comprised of alluvium.

Soil characteristics affecting vegetation include soil hydrology and temperature. The soils are somewhat poorly drained with a shallow water table throughout the year. Aquic conditions and redox concentrations begin at 18 inches of depth. These conditions restrict vegetation to primarily facultative and facultative wet wetland species. An umbric epipedon hints at low natural soil fertility levels, though flooding deposits may contribute to soil fertility.

Correlated soil components in MLRA 236:
D36-Western maritime scrub loamy flood plains
Fluvaquentic Cryaquepts

Table 5. Representative soil features

Parent material	(1) Alluvium
Surface texture	(1) Silt loam
Drainage class	Somewhat poorly drained
Permeability class	Moderate
Soil depth	60 – 0 in
Surface fragment cover <=3"	Not specified
Surface fragment cover >3"	Not specified
Available water capacity (0-10in)	2 – 2.4 in
Soil reaction (1:1 water) (0-10in)	4.8 – 6
Subsurface fragment volume <=3" (Depth not specified)	Not specified
Subsurface fragment volume >3" (Depth not specified)	Not specified

Table 6. Representative soil features (actual values)

Drainage class	Somewhat poorly drained to poorly drained
Permeability class	Moderate
Soil depth	60 – 0 in
Surface fragment cover <=3"	0 %
Surface fragment cover >3"	0 %
Available water capacity (0-10in)	2 – 3 in
Soil reaction (1:1 water) (0-10in)	4.8 – 6
Subsurface fragment volume <=3" (Depth not specified)	0 %
Subsurface fragment volume >3" (Depth not specified)	0 %

Ecological dynamics

This site describes convex berm features along low energy rivers on lowland valley flood plains. Local site factors such as soil hydrology and a non-scouring flood regime support one hydrophytic community. The reference plant community is an open tall scrubland of one or more willow species. Understory vegetation consists of diverse and dense herbaceous species.

This community is shaped by soil hydrology. Soils are somewhat poorly drained and a support a shallow water table. Aquic conditions are present at 18 inches in the soil profile. These conditions support facultative wet to obligate species resilient to seasonal hypoxic and anoxic conditions. These species are resilient to the low energy scouring caused by occasional, long flooding periods. There is no post-flood community phase described for this site.

Moderate to severe willow browse is common in this site. Moose and caribou may both use this as a food source. This does not appear to affect the ecological processes of the 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. Tealeaf willow-Barclay's willow/bluejoint/field horsetail-purple marshlocks

State 1
Reference State

The reference state supports one community phase, which is distinguished by the developed structure and dominance of the vegetation and by their ecological function and stability. The reference community phase is closed tall scrubland.

This report provides baseline inventory data for this 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
Tealeaf willow-Barclay's willow/bluejoint/field horsetail-purple marshlocks

Figure 7. Typical area of the reference plant community that has dense willow in some areas.

Figure 8. Open areas of the reference plant community that support a mix of graminoids and forbs with willows nearby.

Figure 9. Frequency and canopy cover of plants in community 1.1.

The reference plant community is closed tall scrubland (Viereck et al., 1992) that has forbs and graminoids throughout. The plants in this community commonly are facultative or obligate wetland species that thrive in moist soil conditions. The community consists of a mix of tealeaf willow (Salix pulchra) and Barclay’s willow (S. barclayi) with large patches of bluejoint (Calamagrostis canadensis) and forbs, such as field horsetail (Equisetum arvense), purple marshlocks (Comarum palustre), and Canadian burnet (Sanguisorba canadensis). Other species may include arctic raspberry (Rubus arcticus), dwarf bitch (Betula nana), sweetgale (Myrica gale), bog blueberry (Vaccinium uliginosum), water sedge (Carex aquatilis), Northwest Territory sedge (Carex utriculata), woolly geranium (Geranium erianthum), fireweed (Chamerion angustifolium), and violets (Viola spp.). The ground cover includes mosses, including sphagnum mosses (Sphagnum spp.) and feathermosses (Hylocomium splendens, Ptilium crista-castrensis, and Pleurozium schreberi); herbaceous litter; woody litter; and water. Some areas are bare soil.

Dominant plant species

tealeaf willow (Salix pulchra), shrub
arctic raspberry (Rubus arcticus), shrub
Barclay's willow (Salix barclayi), shrub
bluejoint (Calamagrostis canadensis), grass
field horsetail (Equisetum arvense), other herbaceous
purple marshlocks (Comarum palustre), other herbaceous
Canadian burnet (Sanguisorba canadensis), other herbaceous

Additional community tables

Table 7. Community 1.1 plant community composition

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

Supporting information

Inventory data references

Modal points for Community 1.1 08SS08405 09SS02204 09SS02502 10TD12307 10TD12505 10TD13607

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.

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
Sue Tester
Michael Margo
Kendra Moseley
Steph Schmit
Jamin Johanson
Steff Shoemaker

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	09/23/2026
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 R236XY173AK

Subarctic Riparian Complex Loamy Flood Plains

Last updated: 2/13/2024 Accessed: 09/23/2026

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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: 09/23/2026