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Ecological site AX001X01X002

Mesic Udic Flood Plain Forest

Last updated: 5/15/2025
Accessed: 05/20/2025

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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): 001X–Northern Pacific Coast Range, Foothills, and Valleys

This area consists of a long and narrow range of mountains with associated foothills and valleys that parallels the Pacific Ocean. This area is entirely within the Pacific Border Province of the Pacific Mountain System in Oregon and Washington. MLRA 1 is bounded on the north by the highest elevations of the Olympic Mountains and the strait of Juan de Fuca, and by the Klamath Mountains on the south. The Washington portion of this MLRA is primarily composed of young Tertiary sedimentary rocks (siltstone and sandstone) mixed with some volcanic rocks of the same age. Glacial till and outwash deposits are also found in the northern half of this area in Washington. Much of this area is accreted terrane formed by tectonic processes. The average annual precipitation ranges from 60 to 200 inches (1,525 to 5,580 millimeters), increasing with elevation. Most of the precipitation in this area occurs during low-intensity, Pacific frontal storms and is evenly distributed throughout fall, winter, and spring.

The dominant soil orders in this MLRA are Andisols, Inceptisols, and Ultisols. Soil depths broadly range from shallow to very deep. Soils are primarily well drained, however poorly drained soils may be found in depressional areas and on alluvial flood plains. Surface textures are typically medial and loamy or clayey. Soils in this area dominantly have a mesic or frigid temperature regime and a udic moisture regime. Soils with aquic moisture regimes and cryic temperature regimes also occur.

Ecological site concept

Mesic Udic Flood Plain Forest sites occur on low terraces in river valleys. These sites are rarely flooded, i.e., the average probability of flooding is between one and five percent for every year. Mesic Udic Flood Plain Forests are characterized by a dense overstory of western hemlock (Tsuga heterophylla) and bigleaf maple (Acer macrophyllum). Western hemlock is a shade-tolerant species, and may continually regenerate in the shaded understory, but deciduous tree regeneration is generally limited to canopy gaps. The understory shrub layer is dominated by salmonberry (Rubus spectabilis) and vine maple (Acer circinatum). The forb layer is typically composed of western swordfern (Polystichum munitum), small enchanter’s nightshade (Circaea alpina), threepetal bedstraw (Galium trifidum), redwood-sorrel (Oxalis oregana), and coastal hedgenettle (Stachys cooleyae).

Associated sites

F004AA001WA	Udic Flood Plain Forest Isomesic Udic Flood Plain Forests occur at lower elevations in the Sitka Spruce belt. Isomesic Udic Flood Plain Forests are readily distinguished by the presence of Sitka spruce (Picea sitchensis).

F004AA001WA

Udic Flood Plain Forest

Isomesic Udic Flood Plain Forests occur at lower elevations in the Sitka Spruce belt. Isomesic Udic Flood Plain Forests are readily distinguished by the presence of Sitka spruce (Picea sitchensis).

Similar sites

AX001X01X003	Mesic Udic Alluvial Terrace Forest Mesic Udic Alluvial Terraces occur on higher terraces above Mesic Udic Flood Plain Forests. Plant communities in Mesic Udic Alluvial Terrace Forests more closely resemble those of upland forests.
AX001X01X001	Temperate Flood Plain Shrubland Temperate Flood Plain Shrublands occur between stream channels and adjacent Mesic Udic Flood Plain Forest sites. Temperate Flood Plain Shrublands have higher shrub cover versus tree cover than Mesic Udic Flood Plain Forests.
AX001X01X200	Temperate Wet Meadow Temperate Wet Meadow sites occur on depressions and seeps adjacent to or surrounded by Mesic Udic Flood Plain Forests. Temperate Wet Meadow sites lack tree cover.

AX001X01X003

Mesic Udic Alluvial Terrace Forest

Mesic Udic Alluvial Terraces occur on higher terraces above Mesic Udic Flood Plain Forests. Plant communities in Mesic Udic Alluvial Terrace Forests more closely resemble those of upland forests.

AX001X01X001

Temperate Flood Plain Shrubland

Temperate Flood Plain Shrublands occur between stream channels and adjacent Mesic Udic Flood Plain Forest sites. Temperate Flood Plain Shrublands have higher shrub cover versus tree cover than Mesic Udic Flood Plain Forests.

AX001X01X200

Temperate Wet Meadow

Temperate Wet Meadow sites occur on depressions and seeps adjacent to or surrounded by Mesic Udic Flood Plain Forests. Temperate Wet Meadow sites lack tree cover.

Table 1. Dominant plant species

Tree	(1) Tsuga heterophylla (2) Acer macrophyllum
Shrub	(1) Rubus spectabilis (2) Acer circinatum
Herbaceous	(1) Polystichum munitum (2) Circaea alpina

Legacy ID

F001XA002WA

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Physiographic features

This site primarily occurs on terraces on river valleys. Mesic Udic Flood Plain Forest sites occur on higher flood plain positions and low alluvial terraces. These sites only flood occasionally. As a result, these flood plain forest sites support mature trees and are not subject to as frequent severe disturbance from intense flood events.

Table 2. Representative physiographic features

Landforms	(1) River valley > Terrace
Flooding duration	Brief (2 to 7 days)
Flooding frequency	Rare to occasional
Ponding frequency	None
Elevation	328 – 1,640 ft
Slope	15%
Water table depth	59 in
Aspect	W, NW, N, NE, E, SE, S, SW

Climatic features

This site occurs in a mesic temperature regime, and udic moisture regime. Precipitation arrives mostly via low-intensity, Pacific frontal storms. Precipitation is unevenly distributed, with the lowest amounts on the leeward side of the Coast Range mountains. Precipitation falls largely as snow in higher elevations. Precipitation is evenly distributed throughout the fall, winter, and spring, while summers are dry. Air temperatures vary significantly along the elevation gradient.

Table 3. Representative climatic features

Frost-free period (characteristic range)	180-240 days
Freeze-free period (characteristic range)
Precipitation total (characteristic range)	69-108 in

Soil features

The soils that support this ecological site occur in the mesic soil temperature regime and the udic soil moisture regime. Lowdivide soils are well drained, very deep, formed from mixed geology alluvium, and are found on alluvial terraces in river valleys. Saturated hydraulic conductivity is high or very high throughout. These soils have occasional or rare flooding potential in January, February, March, and April. These soils have a texture of silt loam or loam in the upper 20 to 30 inches, and loamy sand or sand with greater than 35 percent rock fragments below that. Flooding frequency is a limiting factor for plant growth. Although representative of this site, these soils may exist across multiple ecological sites because of naturally variable slope, texture, rock fragments, and pH. An on-site soil pit and the most current ecological site key are necessary to classify a site.

Table 4. Representative soil features

Parent material	(1) Alluvium
Surface texture	(1) Silt loam (2) Loam (3) Sandy loam
Drainage class	Well drained
Depth to restrictive layer	59 in
Surface fragment cover <=3"	5%
Surface fragment cover >3"	Not specified
Subsurface fragment volume <=3" (Depth not specified)	Not specified
Subsurface fragment volume >3" (Depth not specified)	Not specified

Ecological dynamics

Plant community dynamics of Mesic Udic Flood Plain Forest sites are driven primarily by the frequency and intensity of flooding events. Alpine snowmelt from high elevation generates large amounts of water and may result in high-intensity flood events. Rarely, flood waters will exceed the capacity of the flood plain and will breach the terrace riser. This ecological site is situated in the transition zone between flood plain shrublands and upland forests. Dominant species in the reference community are generally tolerant of rare flooding events.

High force windstorms are a major source of large-scale disturbance to these riparian forests. Blowdown events are often severe and may be stand replacing. (Van Pelt, 2007). Wildfires are an additional source of disturbance, though they occur much less frequently. The fire regime of this forest type is characterized by infrequent, severe fire events. The fire return interval is very high, 100 to nearly 1,000 years (FEIS, 2012). Major 100 to 500-year flood events may remove litter and scour the mineral soil surface. Windstorms, intense floods, and stand-replacing fire events are all capable of inducing high woody species mortality on these sites. The removal of overstory species will generally favor the regeneration of shade-intolerant species in the aftermath of extreme disturbance events. Stand-replacing disturbance events provide a major source of instream wood recruitment in these riparian systems (Martens et al., 2020).

In the immediate aftermath of a major disturbance event, willow species (Salix spp.) are generally the first to recruit to the site. The most common willow species found on this site are Scouler’s willow (Salix scouleriana) and Sitka willow (Salix sitchensis). Along with willow the sparse understory of the early seral stage consists primarily of western swordfern (Polystichum munitum) and stinging nettle (Urtica dioica). Within a few years, red alder (Alnus rubra) and black cottonwood (Populus balsamifera ssp. trichocarpa) will recruit to the site. As time passes, Western hemlock (Tsuga heterophylla) and bigleaf maple (Acer macrophyllum) will begin to regenerate in the understory. At this point, the forest consists of a single-story canopy with a diminished understory. Western hemlock and bigleaf maple will eventually replace black cottonwood and red alder as the dominant tree species. Individual tree mortality due to windthrow and continual shade-tolerant species regeneration creates a varied-age stand with small canopy gaps.

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

1.1A	-	High-intensity disturbance
1.2A	-	Time without disturbance
1.3B	-	High-intensity disturbance
1.3A	-	Time without disturbance
1.4B	-	High-intensity disturbance
1.4A	-	Time without disturbance
1.5A	-	Time without disturbance
1.5B	-	High-intensity disturbance

State 1
Reference

The Reference state is comprised of five communities is varying stages of regeneration. Communities in the Reference state range from a sparse, emergent understory of shrubs and forbs that is found in the early aftermath of disturbance, to mature stands of conifers, deciduous trees, and shrubs.

Dominant plant species

western hemlock (Tsuga heterophylla), tree
bigleaf maple (Acer macrophyllum), tree
black cottonwood (Populus balsamifera ssp. trichocarpa), tree
red alder (Alnus rubra), tree
willow (Salix), shrub
California blackberry (Rubus ursinus), shrub
vine maple (Acer circinatum), shrub
salmonberry (Rubus spectabilis), shrub
western swordfern (Polystichum munitum), other herbaceous
bedstraw (Galium), other herbaceous
stinging nettle (Urtica dioica), other herbaceous
small enchanter's nightshade (Circaea alpina), other herbaceous

Community 1.1
Mountain Hemlock, Bigleaf Maple, Salmonberry, Vine Maple, Western Swordfern, Small Enchanter's Nightshade

Structure: multistory with small gap dynamics Western hemlock and bigleaf maple are the dominant tree species in the reference community. Individual mortality of mature trees creates small canopy gaps. Western hemlock tolerates shade and will continually regenerate in the understory. Deciduous regeneration is generally limited to canopy gaps. The understory consists of diverse shrub, forb, and grass layers.

Community 1.2
Willow, Western Swordfern, and Stinging Nettle

Structure: sparse understory of emergent shrubs, forbs, and grasses This community follows a stand-replacing disturbance event. Willow quickly establishes where the canopy has been removed. Red alder and black cottonwood seeds may begin to germinate in areas where sunlight continues to reach the mineral soil surface. If downed cottonwood individuals remain on the site, regeneration may occur through sprouting.

Community 1.3
Red Alder, Black Cottonwood, California Blackberry, Vine Maple, and Western Swordfern

Structure: shrubby single story with scattered understory of trees, shrubs, forbs, and grasses This community follows the initial phase of regeneration post-disturbance. As time progresses, red alder and black cottonwood successfully establish. The shrub and forb layers gradually diversify as slow-growing species begin to regenerate.

Community 1.4
Red Alder, Black Cottonwood, Vine Maple, California Blackberry, Western Swordfern, and Bedstraw

Structure: deciduous forest with a mix of shrubs, forbs, and grasses, with conifer regeneration in the understory Red alder and black cottonwood continue to grow and form a discrete canopy layer. Western hemlock begins to regenerate in the understory. Vine maple is a significant understory shrub in this community.

Community 1.5
Red Alder, Western Hemlock, Vine Maple, Salmonberry, and Western Swordfern

Structure: single story with few small openings By this point, black cottonwood has suffered high mortality due to its high susceptibility to rot. Tree mortality creates small canopy openings which are exploited by understory plants. Salmonberry recruits to the site. Western hemlock begins to replace deciduous species and will continually regenerate in the shaded understory.

Pathway 1.1A
Community 1.1 to 1.2

High-intensity disturbance. Severe flooding event that removes existing vegetation, intense windstorm, or stand-replacing wildfire.

Pathway 1.2A
Community 1.2 to 1.3

Time without disturbance allows regeneration, growth, and progression to a later seral stage.

Pathway 1.3B
Community 1.3 to 1.2

High-intensity disturbance. Severe flooding event that removes existing vegetation, intense windstorm, or stand-replacing wildfire.

Pathway 1.3A
Community 1.3 to 1.4

Time without disturbance allows regeneration, growth, and progression to a later seral stage.

Pathway 1.4B
Community 1.4 to 1.2

High-intensity disturbance. Severe flooding event that removes existing vegetation, intense windstorm, or stand-replacing wildfire.

Pathway 1.4A
Community 1.4 to 1.5

Time without disturbance allows regeneration, growth, and progression to a later seral stage. Individual tree mortality creates small canopy openings.

Pathway 1.5A
Community 1.5 to 1.1

Time without disturbance allows regeneration, growth, and progression to a later seral stage. Vertical stratification increases and forb diversity increases. Individual tree mortality creates varied-age patches.

Pathway 1.5B
Community 1.5 to 1.2

High-intensity disturbance. Severe flooding event that removes existing vegetation, intense windstorm, or stand-replacing wildfire.

Additional community tables

Supporting information

Other references

Breemen, Nico van. “How Sphagnum Bogs down Other Plants.” Trends in Ecology & Evolution 10, no. 7 (July 1, 1995): 270–75. 90007-1.

Dwire, K. and Kauffman, J. 2003. Fire and Riparian Ecosystems in Landscapes in the Western United States. Forest Ecology and Management, Vol. 178 pg. 61-74.

Franklin, Jerry F.; Cromack, Kermit, Jr.; Denison, William; [and others]. 1981. Ecological characteristics of old-growth Douglas-fir forests. Gen. Tech. Rep. PNW-118. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 48 p. [7551]

Gavin, D., Brubaker, L. (2015). The Modern Landscape of the Olympic Peninsula. In: Late Pleistocene and Holocene Environmental Change on the Olympic Peninsula, Washington. Ecological Studies, vol 222. Springer, Cham. https://doi.org/10.1007/978-3-319-11014-1_1

Geertsema, Marten & Pojar, James. (2007). Influence of landslides on biophysical diversity — A perspective from British Columbia. Geomorphology. 89. 55-69. 10.1016/j.geomorph.2006.07.019.

Goheen, E.M. and Willhite, E.A. 2006. Field Guide to Common Diseases and Inspect Pests of Oregon and Washington Conifers. Portland, Oregon: USDA Forest Service, Pacific Northwest Region R6-NR-FID-PR-01-06.

Hanley, D.P and D.M. Baumgartner. 2002. Forest Ecology in Washington. Washington State University Extension Publishing. Technical Report EB 1943.

Hanson, E.J., D.L. Azuma and B.A. Hiserote. 2002. Site Index Equations and Mean Annual Increment Equations for Pacific Northwest Research Station Forest Inventory and Analysis Inventories, 1985-2001. USDA Forest Service Pacific Northwest Research Station, Research Note PNW-RN-533.

Hemstrom, M., Franklin, J. 1982. Fire and Other Disturbances of the Forests in Mount Rainier National Park. Quaternary Research, Vol 18 pp 32-61.

James K. Agee and Mark H. Huff. 1987. Fuel succession in a western hemlock/Douglas-fir forest. Canadian Journal of Forest Research. 17(7): 697-704. https://doi.org/10.1139/x87-112

Nielsen, E. M., R. L. Brunner, C. Copass and L. K. Wise, 2021. Olympic National Park map class descriptions. National Park Service, Fort Collins.

Pojar J., and MacKinnon. 1994. Plants of the Pacific Northwest Coast. Lone Pine, Vancouver, British Columbia. 528 pages.

PRISM Climate Group, Oregon State University, http://prism.orgeonstate.edu, visited October 2023.

Reed Wendel, Darlene Zabowskl "Fire History within the Lower Elwha River Watershed, Olympic National Park, Washington," Northwest Science, 84(1), 88-97, (1 January 2010)

Rochefort, R.M. and Peterson, D.L. 1996. Temporal and Spatial Distribution of Trees in Subalpine Meadows of Mount Rainier National Park. Arctic and Alpine Research, Vol. 28, No. 1 pp 52-59.

Seastedt, T.R., Adams, G.A. 2001. Effects of Mobile Tree Islands on Alpine Tundra Soils. Ecology, Vol 82 pp 8-17.

Smith, K., G. Kuhn, and L. Townsend. 2008. Culmination of Mean Annual Increment for Indicator Tree Species in the State of Washington. USDA-NRCS Technical Note Forestry-9.
United States Department of Agriculture, Forest Service, 2015. Silvics Manual Vol 1. http://na.fs.fed.us/spfo/pubs/silvics_manual/Volume_1/vol1_Table_of_contents.htm, visited December 2015.

United States Department of Agriculture, Natural Resources Conservation Service, and United States Department of the Interior, National Park Service. 2014. Ecological Site Descriptions for North Cascades National Park Complex, Washington.

United States Department of Agriculture, Natural Resources Conservation Service, and United States Department of the Interior, National Park Service. Ecological Site Descriptions for Mount Rainier National Park, Washington.

Van Pelt, R. 2007. Identifying Mature and Old Forests in Western Washington. Washington State Department of Natural Resources, Olympia, WA. 104 p

Washington Department of Natural Resources, Natural Heritage Program. 2015. Ecological Systems of Washington State. A Guide to Identification.

Wood, David, and Moral, Roger del. “Mechanisms of Early Primary Succession in Subalpine Habitats on Mount St. Helens.” Ecology 68, no. 4 (1987).

Zhao, Yunpeng, Chengzhu Liu, Simin Wang, Yiyun Wang, Xiaoqing Liu, Wanqing Luo, and

Xiaojuan Feng. “‘Triple Locks’ on Soil Organic Carbon Exerted by Sphagnum Acid in Wetlands.” Geochimica et Cosmochimica Acta 315 (December 2021): 24–37. https://doi.org/10.1016/j.gca.2021.09.028

Contributors

Alec Haulotte
Erin Kreutz
Max Ross
Abigail Field
Erik Dahlke

Approval

Grant Petersen, 5/15/2025

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	05/16/2025
Approved by	Grant Petersen
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

Click on box and path labels to scroll to the respective text.

Ecosystem states

1. Reference

State 1 submodel, plant communities

1.1. Mountain Hemlock, Bigleaf Maple, Salmonberry, Vine Maple, Western Swordfern, Small Enchanter's Nightshade

1.2. Willow, Western Swordfern, and Stinging Nettle

1.3. Red Alder, Black Cottonwood, California Blackberry, Vine Maple, and Western Swordfern

1.4. Red Alder, Black Cottonwood, Vine Maple, California Blackberry, Western Swordfern, and Bedstraw

1.5. Red Alder, Western Hemlock, Vine Maple, Salmonberry, and Western Swordfern

Communities 1, 5 and 2 (additional pathways)

1.1. Mountain Hemlock, Bigleaf Maple, Salmonberry, Vine Maple, Western Swordfern, Small Enchanter's Nightshade

1.5. Red Alder, Western Hemlock, Vine Maple, Salmonberry, and Western Swordfern

1.2. Willow, Western Swordfern, and Stinging Nettle

1.1A	-	High-intensity disturbance
1.2A	-	Time without disturbance
1.3B	-	High-intensity disturbance
1.3A	-	Time without disturbance
1.4B	-	High-intensity disturbance
1.4A	-	Time without disturbance
1.5A	-	Time without disturbance
1.5B	-	High-intensity disturbance

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Natural ResourcesConservation Service

Ecological site AX001X01X002

Mesic Udic Flood Plain Forest

Last updated: 5/15/2025 Accessed: 05/20/2025

General information

MLRA notes

Ecological site concept

Associated sites

Similar sites

Table 1. Dominant plant species

Legacy ID

Ecosystem states

State 1 submodel, plant communities

Communities 1, 5 and 2 (additional pathways)

Natural Resources
Conservation Service

Last updated: 5/15/2025
Accessed: 05/20/2025