Natural Resources
Conservation Service
Ecological site F003XN926WA
Cryic/Udic Active Natural Disturbance
Last updated: 1/30/2025
Accessed: 09/08/2026
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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
Related National Park Service Plant Alliances:
Alnus viridis ssp. sinuate Shrubland, Abies amabilis - Abies lasiocarpa Forest and Woodland Alliance, Abies amabilis - Tsuga heterophylla - (Pseudotsuga menziesii) / (Rhododendron albiflorum) Cold Forest Alliance (Crawford 2009).
This ecological site is related to the United States Forest Service Plant Association Groups: Cool VAME and Mesic VAME (Silver Fir Series). (Henderson 1992 p.83)Associated sites
F003XN924WA Low Cryic/Udic West Coniferous
F003XN925WA High Cryic/Udic Coniferous
F003XN929WA Low Cryic/Udic East Coniferous
R003XN512WA Subalpine Parkland Active Natural Soil Disturbance
Table 1. Dominant plant species
Tree (1) Alnus viridis ssp. sinuata
Shrub (1) Sambucus racemosa
Herbaceous (1) Veratrum viride
(2) Athyrium filix-feminaPhysiographic features
This native plant community is of limited extent on mountain slope positions at higher elevations of the North Cascades. Typically this site is confined to avalanche paths and runout areas or similar areas with a higher frequency of disturbance such as talus slopes or debris torrent deposits.
This ecological site has only been mapped within the boundary of the North Cascades National Park Complex. This site, where mapped, ranged from 2000 to 7000 feet in elevation. The table below refers to the representative elevations of this site.Table 2. Representative physiographic features
Landforms (1) Avalanche chute
(2) Valley side
(3) Mountain slope
Flooding frequency None Ponding frequency None Elevation 3000 – 6000 ft Slope 15 – 65 % Water table depth 60 – 0 in Aspect Aspect is not a significant factor Climatic features
This ecological site receives most of its annual precipitation from October to April in the form of snow that will commonly persist into late spring and early summer. The mean annual precipitation ranges from 60 to 115 inches and the mean annual temperature ranges from 31 to 47 degrees Fahrenheit. Generally this site occupies areas with cool dry summers and cold 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) 60 days Freeze-free period (average) 90 days Precipitation total (average) 120 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
This ecological site is not influenced by wetland or riparian water features.
Soil features
Applicable soils: Stetattle, deciduous, Triumph, deciduous.
The soils that support this native plant community occur in the cryic soil temperature regime (average annual temperature less than 8 degrees C, with less than 5 degrees C difference from winter to summer) and udic soil moisture regime (the rooting zone is usually moist throughout the winter and the majority of summer). These soils are well drained and deep to very deep. Generally these soils have a mantle of material with significant volcanic ash influence overlying colluvium. The upper mantle is characterized by a low bulk density and high water holding capacity although an abundance of coarse fragments within the profile may limit the amount of moisture available. Soil profiles under this plant community will typically have a darker color than their coniferous forest counterparts owing to the abundance of deciduous forest litter and herbaceous root matter incorporated into the soil profile.
A blank entry under soil depth column indicates no depth restriction within the soil profile.
For more information on soils and their terminology, please refer to Soil taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys (Soil Survey Staff, 1999; http://soils.usda.gov/technical/classification/taxonomy/).Table 4. Representative soil features
Surface texture (1) Medial fine sandy loam
(2) Ashy sandy loam
Family particle size (1) Loamy
Drainage class Well drained Permeability class Moderately rapid to very rapid Soil depth 40 – 0 in Surface fragment cover <=3" 5 – 25 % Surface fragment cover >3" 0 – 25 % Available water capacity
(0-40in)4.2 – 15.99 in Soil reaction (1:1 water)
(0-40in)4.3 – 6.5 Subsurface fragment volume <=3"
(Depth not specified)35 – 80 % Subsurface fragment volume >3"
(Depth not specified)35 – 60 % Ecological dynamics
This site is found on cold, moist, higher elevation active avalanche chutes. Sitka alder (Alnus viridis ssp. sinuata) is the dominant species and will grow almost prostrate in response to snow load and the force of avalanches. Repetitious disturbance by avalanches does not allow for the establishment of a forested overstory, but seedlings of tree species, such as subalpine fir (Abies lasiocarpa), mountain hemlock (Tsuga mertensiana) and Pacific silver fir (Abies amabilis) may encroach from the forest edges. Over time, the majority of these rigid-trunked species will be snapped off by the force of an avalanche. Common understory shrubs include red elderberry (Sambucus racemosa), salmonberry (Rubus spectabilis), Sitka mountain-ash (Sorbus sitchensis), prickly currant (Ribes lacustre); common forbs include false hellebore (Veratrum viride), common ladyfern (Athyrium filix-femina), fireweed (Chamerion angustifolium) and Sitka valerian (Valeriana sitchensis).
State and transition model
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Figure 4. State and Transition Model
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
ReferenceCommunity 1.1
Sitka Alder, Red Elderberry, False Hellebore, and Common Ladyfern
Figure 5. Reference Community (mid-ground on slope)
Structure: mosaic of tall shrubs, short shrubs and forbs.
Sitka alder will form large areas of continuous canopy cover especially toward the lower end of avalanche chutes where the slope becomes less steep. These areas tend to have less varied shrub composition but higher amounts of forbs and ferns such as false hellebore, fireweed (Chamerion angustifolium) and common ladyfern. Where Sitka alder becomes more patchy, other tall shrubs such as red elderberry, salmonberry, Sitka mountain-ash and prickly currant will be present. These species don’t take on a prostrate form, instead they resprout basally, becoming stunted and multi-stemmed. All of these species (with the possible exception of prickly currant) can readily sprout from the root crown and are therefore able to persist in avalanche chutes.Community 1.2
Subalpine Fir, Mountain Hemlock, Sitka Alder, Red Elderberry, False Hellebore, and Common LadyfernStructure: sparse overstory species ‘invading’ avalanche path from the edges.
The forest surrounding avalanche chutes provide a continual seed source for recruitment into the community. Typically these rigid-stemmed species will not survive repeated onslaughts from avalanches when they establish in the main snow path. They can, however, slowly encroach from the forest edges where mature trees offer some buffer against less forceful snow movements. Over time and in the right circumstances (less overall snowfall, more stable snowpack), this can lead to a narrowing of the original chute.Pathway 1.1A
Community 1.1 to 1.2This pathway represents an extended time with minimal major avalanche disturbance.
Pathway 1.2A
Community 1.2 to 1.1This pathway represents a particularly powerful avalanche or serious of avalanches which reclaim the original extent of the avalanche chute.
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 understory composition
Common name Symbol Scientific name Nativity Height (ft) Canopy cover (%) Forb/Herbgreen false hellebore VEVI Veratrum viride Native 1–3 1–40 Sitka valerian VASI Valeriana sitchensis Native 0.5–2 1–20 fireweed CHANA2 Chamerion angustifolium ssp. angustifolium Native 1–3 1–15 Fern/fern allycommon ladyfern ATFI Athyrium filix-femina Native 1–3 1–40 Shrub/SubshrubSitka alder ALVIS Alnus viridis ssp. sinuata Native 3–15 30–80 salmonberry RUSP Rubus spectabilis Native 2–6 5–40 Sitka mountain ash SOSIS2 Sorbus sitchensis var. sitchensis Native 2–10 5–40 red elderberry SARA2 Sambucus racemosa Native 2–12 5–30 prickly currant RILA Ribes lacustre Native 1–4 1–15 Table 7. Community 1.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Table 8. Representative site productivity
Common name Symbol Site index low Site index high CMAI low CMAI high Age of CMAI Site index curve code Site index curve basis Citation subalpine fir ABLA 50 70 39 63 120 – – Supporting information
Inventory data references
Type Locality Plot ID: 07-PHR-054
Type locality
Location 1: Skagit County, WA Township/Range/Section T35N R14E S16 UTM zone N UTM northing 5375979 UTM easting 648541 Latitude 48° 31′ 8″ Longitude 120° 59′ 19″ Other references
Agee, J.K. 1993. Fire ecology of Pacific Northwest forests. Covelo, CA: Island Press. 493 pages.
Bebi, P., Kulakowski, D. & Rixen, C. 2009. Snow avalanche disturbances in forest ecosystems – State of research and implications for management. Forest Ecology and Management 257: 1883-1892.
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. 196 pages.
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. 1994. Baltimore, MD: The Johns Hopkins University Press. 649 pages.
Pojar, J., and A. MacKinnon. 1994. Plants of the Pacific Northwest Coast. Lone Pine,
Vancouver, British Columbia. 528 pages.
Rixen, C., Haag, S., Kulalowski, D. & Bebi, P. 2007. Natural avalanche disturbance shapes plant diversity and species composition in subalpine forest belt. Journal of Vegetation Science 18: 735-742.
Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys. 2nd edition. Natural Resources Conservation Service. U.S. Department of Agriculture Handbook 436. http://soils.usda.gov/technical/classification/taxonomy/
Stokes, A., Mine, F., Mao, Z., Brancheriau, L. & Vandvik, V. 2012. Multi-stemming and mechanical traits ensure persistence of subalpine woody plants exposed to a disturbance gradient. Journal of Vegetation Science 23: 325.
Contributors
Kathryn 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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