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Conservation Service
Ecological site F003XN921WA
Frigid/Udic Coniferous
Last updated: 1/30/2025
Accessed: 09/16/2026
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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.
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Figure 1. Mapped extent
Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated.
Classification relationships
This ecological site falls within the National Vegetation Classification Group G240 - North Pacific Maritime Douglas-fir-Western Hemlock Forest.
This ecological site includes the following USDA Forest Service Plant Association Groups: Mesic GASH-BENE, Mesic POMU, Moist POMU.Associated sites
F003XN920WA Frigid Riparian Forest
Frigid riparian forests.
F003XN922WA Frigid/Udic Active Natural Disturbance
Frigid/udic active natural disturbance.
F003XN924WA Low Cryic/Udic West Coniferous
Low cryic/udic west side coniferous forests.
Table 1. Dominant plant species
Tree (1) Tsuga heterophylla
(2) Thuja plicataShrub (1) Acer circinatum
(2) Vaccinium parvifoliumHerbaceous (1) Linnaea borealis
(2) Polystichum munitumPhysiographic features
This native plant community occurs across many landscape positions generally at lower elevations along the west slope of the North Cascades. Dominating the mountain slopes of the frigid/udic soil temperature/moisture regime, this site also extends to some stream terraces of glacial valleys.
This ecological site has only been mapped within the boundary of the North Cascades National Park Complex.Table 2. Representative physiographic features
Landforms (1) Mountain slope
(2) Valley side
(3) Stream terrace
Flooding duration Very brief (4 to 48 hours) to brief (2 to 7 days) Flooding frequency None to occasional Ponding frequency None Elevation 800 – 3900 ft Slope 5 – 100 % Water table depth 20 – 0 in Aspect Aspect is not a significant factor Climatic features
This ecological site receives most of its annual precipitation from October to April. The mean annual precipitation ranges from 35 to 106 inches and the mean annual temperature ranges from 37 to 51 degrees Fahrenheit. Generally this site occupies areas with warm dry summers and cool wet winters.
Precipitation and temperature data in the tables below was extracted from: PRISM Climate Group, Oregon State University, http://prism.oregonstate.edu, created February 2004. Information from the Ross Dam weather station, was used by the PRISM Climate Group to generate climate data for the North Cascades region.Table 3 Representative climatic features
Frost-free period (average) 90 days Freeze-free period (average) 120 days Precipitation total (average) 110 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
In general, this ecological site is not influenced by wetland or riparian water features but may be found on stream terraces or adjacent to wetland and riparian areas. Occasionally and for brief amounts of time, the site may be flooded by adjacent rivers and streams but overall this has an insignificant influence on the plant community. Typically the Deerlick or Skymo soil series are present in the areas subject to flooding.
Soil features
Applicable soils: Cosho, Damnation, Deerlick, Easy, Ledeir, Ragged, Skymo, Thorton, Tricouni. Based on the composition of detailed soil map units and dominance of mountain slope landform positions, modal soils under this ecological site are the Cosho, Ragged, Thorton, and Tricouni soil series.
The soils that support this native plant community occur in the frigid soil temperature regime and the udic soil moisture regime. These soils are moderately well to well drained and range from shallow bedrock controlled soils to very deep soils. Generally these soils have a mantle of material with significant volcanic ash influence overlying glacial till or colluvium. The upper mantle is characterized by a low bulk density and a high water holding capacity. Soil moisture is not a limiting factor to forest growth on these soils owing to abundance of precipitation and the inherent water holding properties of soils influenced by volcanic ash. Under ideal soil forming conditions enhanced by landscape stability and therefore longevity of pedogenic processes, Spodosols such as the Easy and Ledeir soil series will develop in soils with volcanic ash influence. Soil properties of these Spodosols are very similar to the other soils found under this native plant community, but morphologically Spodosols are visually distinct because of the typically bright albic and spodic horizon sequence in the upper soil profile. Weak expression of this morphology may be visible in the Andisols and Inceptisols of this grouping but generally these soils exhibit an ochric epipedon and cambic subsurface diagnostic horizon.
A blank entry under soil depth column indicates no depth restriction within the soil profile.Table 4. Representative soil features
Surface texture (1) Ashy sandy loam
(2) Ashy loamy sand
Family particle size (1) Loamy
Drainage class Moderately well drained to well drained Permeability class Moderately rapid to rapid Soil depth 10 – 0 in Surface fragment cover <=3" 0 – 10 % Surface fragment cover >3" 0 – 10 % Available water capacity
(0-40in)4.13 – 15.99 in Soil reaction (1:1 water)
(0-40in)3.5 – 6.5 Subsurface fragment volume <=3"
(Depth not specified)5 – 65 % Subsurface fragment volume >3"
(Depth not specified)0 – 35 % Ecological dynamics
This site is found in the cool, moist, lower slopes of the Cascades up to approximately 4600 feet, depending on aspect. It can be found lower in elevation on north- and east-facing slopes and higher on south- and west-facing ones. Western hemlock (Tsuga heterophylla) and western redcedar (Thuja plicata) are the dominant overstory species, often with a co-dominant Douglas-fir (Pseudotsuga menziesii) component. The heavy shade of a hemlock/redcedar forest favors the gradual replacement of Douglas-fir with these more shade-tolerant trees in the absence of a major disturbance. Paper birch (Betula papyrifera), grand fir (Abies grandis) and bigleaf maple (Acer macrophyllum) may all be present, but only as minor overstory components. The most common disturbance on this site is patchy, small pockets of wind-thrown overstory trees, which often occur in conjunction with either root-, butt- or stem-rot. The resulting openings in the canopy allow some sunlight to reach the forest floor, which benefits the understory. The historic fire regime would have been one of low frequency (150-300+ years) and moderate to high intensity. These fires would, in effect, be stand-replacing although individual trees or patches of trees would survive, providing a seed source for reestablishment. The more open the forest canopy, the more dense and diverse the understory. There have been very minimal post-European settlement impacts on the dynamics of this ecological site. Sporadic mining and timber harvests occurred from circa 1870 through World War II but the rough terrain prevented sustained efforts. The construction of the three Skagit River dams (Diablo, Ross and Gorge) required intensive, but narrowly focused, logging. Vine maple (Acer circinatum), red huckleberry (Vaccinium parvifolium), Cascade Oregongrape (Mahonia nervosa), prince’s pine (Chimaphila umbellata) and salal (Gaultheria shallon) are the main shrub species in areas where there is a relatively low overstory canopy closure while twinflower (Linnaea borealis), western swordfern (Polystichum munitum), western rattlesnake plantain (Goodyera oblongifolia) broadleaf starflower (Trientalis borealis ssp. latifolia) and western brackenfern (Pteridium aquilinum) are common forbs.
State and transition model
Custom diagramStandard diagram
Figure 4. F003XN921WA
More interactive model formats are also available. View Interactive Models
More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective textEcosystem states
State 1 submodel, plant communities
State 1
ReferenceCommunity 1.1
Western Hemlock, Western Redcedar, Vine Maple, and Red Huckleberry
Figure 5. Reference Community
Structure: multistory with small gap dynamics.
Western hemlock is the most common overstory species in the historic climax plant community. Western redcedar and Douglas-fir will both be present but there will be minimal Douglas-fir regeneration; grand fir and bigleaf maple would be much smaller components. The dense canopy created by multiple age groups of hemlocks may block most of the sunlight from the forest floor, leading to a sparse understory in some areas. At times vine maple will have this same effect where it grows in thick clumps. Gaps in the mid-canopy and overstory which allow sunlight to reach the ground are where the majority of the understory plants would be found. If there is no mid-canopy the understory will be more continuous. The most common natural disturbance on these sites would be the small gap dynamics following the death of one or two trees. Understory species included in the Canopy Cover Summary table had at least a 50% rate of constancy in 68 inventory plots. For specific data contact site author or your local NRCS office.Community 1.2
Western Hemlock, Western Redcedar, Vine Maple, and Cascade OregongrapeStructure: mosaic of mature overstory and regenerating openings.
CP 1.2 retains some areas that resemble CP 1.1 but also contains moderate sized (2-5 acres) openings. Historically, this spatial pattern would have been caused by pockets of disease (such as annosum root rot or laminated root rot), minor insect infestations or possibly low- to moderate-intensity fires. Depending on the seed sources present, the patches may contain any of the previously mentioned overstory species as well as paper birch and red alder. Many of the shrub species found in the ecological site (including vine maple, red huckleberry, Cascade Oregongrape, bald-hip rose) also respond well to increased sunlight and may delay or even prevent reforestation of the newly formed openings.Community 1.3
Douglas-fir, Western Hemlock, Vine Maple, Salal, and Western SwordfernStructure: single story/shrub.
CP 1.3 is forestland in regeneration, possibly with scattered remnant mature trees; species composition depends on the natural seed sources present and the intensity of disturbance. When resulting from a moderate- to severe fire event, there is a good possibility for shrubs to out-compete tree seedlings. Vine maple, red huckleberry, salal, dwarf rose and Cascade Oregongrape (which may have been only moderately abundant previously) all have the capability to rapidly recover and spread when top-killed, slowing successful overstory regeneration. Seed sources for tree species would be from the surrounding, undisturbed forest and any survivors of the disturbance and would result in a mixed stand which could include Douglas-fir, western hemlock, red alder, paper birch, western redcedar and bigleaf maple.Community 1.4
Douglas-fir, Western Hemlock, Vine Maple, Red Huckleberry, and TwinflowerCP 1.4 is a forest in the competitive exclusion stage, possibly with scattered remnant mature trees; there is increasing competition among individual trees for the available water and nutrients. Canopy closure is almost 100%, leading to a diminished understory however some understory species better adapted to at least partial shade (e.g. red huckleberry or twinflower) will begin to increase. Over time the forest will begin to self-thin due to the elevated competition. Species composition depends on the original seed source(s) available; the forest could be single or mixed-species including Douglas-fir, western hemlock, red alder, paper birch, western redcedar and bigleaf maple.
Community 1.5
Douglas-fir, Western Hemlock, Vine Maple, Red Huckleberry, Twinflower, and Western SwordfernCP 1.5 is a maturing forest which is starting to differentiate vertically. Individual trees are dying (whether due to insects, disease, competition or windthrow) allowing some sunlight to reach the forest floor. This allows for an increase in the understory as well as some pockets of overstory tree species regeneration.
Pathway 1.1A
Community 1.1 to 1.2This pathway is one of minor disturbances which maintain the overall structure of the reference community. The death of one or two trees allows sunlight into the understory, promoting forbs and shrubs as well as the regeneration of overstory species. This perpetuates a multi-storied forest.
Pathway 1.1B
Community 1.1 to 1.2This pathway represents a larger disturbance – an insect infestation, wind storm or rot pocket would create this forest structure. Areas of regeneration would range from approximately 2 to 5 acres.
Pathway 1.1C
Community 1.1 to 1.3This pathway represents a major stand-replacing disturbance such as a high-intensity fire, large scale wind event or major insect infestation.
Pathway 1.2A
Community 1.2 to 1.1This pathway represents growth over time with no further significant disturbance. The areas of regeneration pass through the typical stand phases – competitive exclusion, maturation, understory reinitiation – until they resemble the old-growth structure of the reference community.
Pathway 1.2B
Community 1.2 to 1.3This pathway represents a major stand-replacing disturbance leading to the stand initiation phase of forest development.
Pathway 1.3A
Community 1.3 to 1.4This pathway represents growth over time with no further major disturbance.
Pathway 1.4B
Community 1.4 to 1.3This pathway represents a major stand-replacing disturbance leading to the stand initiation phase of forest development.
Pathway 1.4A
Community 1.4 to 1.5This pathway represents continued growth over time with no further major disturbance.
Pathway 1.5A
Community 1.5 to 1.1This pathway represents no further major disturbance. Continued growth over time, as well as ongoing mortality, leads to continued vertical diversification. The community begins to resemble the structure of the reference community, with small pockets of regeneration and a more diversified understory.
Pathway 1.5B
Community 1.5 to 1.3This pathway represents a major stand-replacing disturbance leading to the stand initiation phase of forest development.
Additional community tables
Table 5. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 6. Community 1.1 forest overstory composition
Common name Symbol Scientific name Nativity Height ft Canopy cover (%) Diameter in Basal area (square ft/acre) Treegrand fir ABGR Abies grandis Native – – – 0 bigleaf maple ACMA3 Acer macrophyllum Native – – – 0 Douglas-fir PSME Pseudotsuga menziesii Native – – – 0 western redcedar THPL Thuja plicata Native – – – 0 western hemlock TSHE Tsuga heterophylla Native – – – 0 Table 7. Community 1.1 forest understory composition
Common name Symbol Scientific name Nativity Height (ft) Canopy cover (%) Forb/Herbclaspleaf twistedstalk STAM2 Streptopus amplexifolius Native 1–3 1–25 broadleaf starflower TRBOL Trientalis borealis ssp. latifolia Native – 1–15 bride's bonnet CLUN2 Clintonia uniflora Native – 1–15 liverleaf wintergreen PYAS Pyrola asarifolia Native – 1–5 western rattlesnake plantain GOOB2 Goodyera oblongifolia Native – 1–5 Fern/fern allywestern swordfern POMU Polystichum munitum Native 1–3 1–60 common ladyfern ATFI Athyrium filix-femina Native 1–3 1–30 western brackenfern PTAQ Pteridium aquilinum Native 1–4 1–25 Shrub/Subshrubsalal GASH Gaultheria shallon Native 1–6 1–60 vine maple ACCI Acer circinatum Native 2–25 1–55 Cascade barberry MANE2 Mahonia nervosa Native 1–3 1–40 red huckleberry VAPA Vaccinium parvifolium Native 1–8 1–35 pipsissewa CHUM Chimaphila umbellata Native – 1–15 twinflower LIBO3 Linnaea borealis Native – 1–15 dwarf rose ROGY Rosa gymnocarpa Native 1–5 1–10 Vine/Lianaorange honeysuckle LOCI3 Lonicera ciliosa Native 1–20 1–5 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 (%) Table 10. Community 1.4 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 11. Community 1.5 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Supporting information
Inventory data references
Type Locality Plot ID: 08-TMR-008
Type locality
Location 1: Whatcom County, WA Township/Range/Section T37N R12E S31 UTM zone N UTM northing 5390293 UTM easting 625187 Latitude 48° 39′ 10″ Longitude 121° 18′ 4″ Other references
Agee, J.K. 1993. Fire ecology of Pacific Northwest forests. Covelo, CA: Island Press. 493 pages.
Crawford, R. C., C. B. Chappell, C. C. Thompson, and F. J. Rocchio. 2009. Vegetation classification of Mount Rainier, North Cascades, and Olympic National Parks. Natural Resource Technical Report NPS/NCCN/NRTR—2009/211. National Park Service, Fort Collins, Colorado. 58 pages.
Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
http://www.fs.fed.us/database/feis/
Henderson, J., R. Lesher, D. Peter, and D. Shaw. 1992. Field guide to the forested plant associations of the Mt. Baker-Snoqualmie National Forest. Technical paper R6-Ecol-TP-028-91.
Miller, Margaret M.; Miller, Joseph W. 1976. Succession after wildfire in the North Cascades National Park complex. In: Proceedings, annual Tall Timbers fire ecology conference: Pacific Northwest; 1974 October 16-17; Portland, OR. No. 15. Tallahassee, FL: Tall Timbers Research Station: 71-83. [6574]
Perry, D.A. Forest Ecosystems. Baltimore, MD: The Johns Hopkins University Press; 1994. 649 pages.
Pojar, J., and A. MacKinnon. 1994. Plants of the Pacific Northwest Coast. Lone Pine,
Vancouver, British Columbia. 528 pages.
Contributors
Kathy Smith
Approval
Kirt Walstad, 1/30/2025
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 01/30/2025 Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
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Presence of water flow patterns:
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Number and height of erosional pedestals or terracettes:
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Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
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Number of gullies and erosion associated with gullies:
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Extent of wind scoured, blowouts and/or depositional areas:
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Amount of litter movement (describe size and distance expected to travel):
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Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
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Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
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Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
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Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
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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:
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Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
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Average percent litter cover (%) and depth ( in):
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Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
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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:
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Perennial plant reproductive capability:
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