Pacific Northwest Avalanche Chute Shrubland

EVT 7083North Pacific Avalanche Chute Shrubland
CES204.854GNRShrubShrubland
Summary
This tall shrubland system occurs throughout mountainous regions of the Pacific Northwest, from the southern Cascades and Coast Ranges north into the mountains of British Columbia. This system occurs on sideslopes of mountains on glacial till or colluvium. These habitats range from moderately xeric to wet and occur on snow avalanche chutes at montane elevations. In the mountains of Washington, talus sites and snow avalanche chutes very often coincide spatially. On the west side of the Cascades, the major dominant species are Acer circinatum, Alnus viridis ssp. sinuata, Rubus parviflorus, and small trees, especially Callitropsis nootkatensis. Forbs, grasses, or other shrubs can also be locally dominant. Prunus virginiana, Amelanchier alnifolia, Vaccinium membranaceum or Vaccinium scoparium, and Fragaria spp. are common species on drier avalanche tracks on the east side of the Cascades. The main feature of this system is that it occurs on steep, frequently disturbed (snow avalanches) slopes. Avalanche chutes can be quite long, extending from the subalpine into the montane and foothill toeslopes.
Source: NatureServe Explorer
Vegetation
On the west side of the Cascades, the major dominant species are Acer circinatum, Alnus viridis ssp. sinuata, Rubus parviflorus, and small trees, especially Callitropsis nootkatensis (= Chamaecyparis nootkatensis). Forbs, grasses, or other shrubs can also be locally dominant. Prunus virginiana, Amelanchier alnifolia, Vaccinium membranaceum or Vaccinium scoparium, and Fragaria spp. are common species on drier avalanche tracks on the east side of the Cascades.
Source: NatureServe Explorer
Environment
This system occurs on sideslopes of mountains on glacial till or colluvium. These habitats range from moderately xeric to wet and occur on snow avalanche chutes at montane elevations. In the mountains of Washington, talus sites and snow avalanche chutes very often coincide spatially. The main feature of this system is that it occurs on steep, frequently disturbed (snow avalanches) slopes. Avalanche chutes can be quite long, extending from the subalpine into the montane and foothill toeslopes.
Source: NatureServe Explorer
Distribution
This system occurs throughout mountainous regions of the Pacific Northwest, from the southern Cascades and Coast Ranges north to the mountains of British Columbia.
Source: NatureServe Explorer
Ecologically Associated Plant Species

Plant species that characterize this ecosystem type, organized by vegetation stratum. These are species ecologically associated with the ecosystem, not confirmed present in any specific area.

Tree canopy

Callitropsis nootkatensis

Shrub/sapling (tall & short)

Acer circinatum, Alnus viridis ssp. sinuata, Amelanchier alnifolia, Prunus virginiana, Rubus parviflorus, Vaccinium membranaceum

Short shrub/sapling

Vaccinium scoparium

Herb (field)

Chamaenerion angustifolium ssp. angustifolium

Nonvascular

Hypogymnia oceanica, Umbilicaria angulata
Source: NatureServe Ecological System assessment
Ecologically Associated Animals (6)

Animal species ecologically associated with this ecosystem type based on NatureServe assessment. These are species whose habitat requirements overlap with this ecosystem, not confirmed present in any specific roadless area.

Mammals (4)

Common NameScientific NameG-Rank
Mountain BeaverAplodontia rufaG5
Long-tailed VoleMicrotus longicaudusG5
American ErmineMustela richardsoniiG5
Shrew-moleNeurotrichus gibbsiiG5

Reptiles (2)

Common NameScientific NameG-Rank
Northwestern GartersnakeThamnophis ordinoidesG5
Common GartersnakeThamnophis sirtalisG5
Source: NatureServe Ecological System assessment
Component Associations (2)

Plant community associations that occur within this ecological system. Associations are the finest level of the U.S. National Vegetation Classification (USNVC) and describe specific, repeating assemblages of plant species. Each association represents a distinct community type that may be found where this ecosystem occurs.

NameG-Rank
Alnus viridis ssp. sinuata / Acer circinatum Shrub SwampG4 NatureServe
Callitropsis nootkatensis / Oplopanax horridus SwampG3 NatureServe
State Conservation Ranks (2)

Subnational conservation status ranks (S-ranks) assigned by Natural Heritage Programs in each state where this ecosystem occurs. S1 indicates critically imperiled at the state level, S2 imperiled, S3 vulnerable, S4 apparently secure, and S5 secure. An ecosystem may be globally secure but imperiled in specific states at the edge of its range.

StateS-Rank
ORSNR
WASNR
Roadless Areas (14)

Inventoried Roadless Areas where this ecosystem is present, identified from LANDFIRE 2024 Existing Vegetation Type spatial analysis. Coverage indicates the proportion of each area occupied by this ecosystem type.

Oregon (2)

AreaForestCoverageHectares
ElkhornWillamette National Forest2.7%103.5
CornpatchWillamette National Forest2.0%60.48

Washington (12)

AreaForestCoverageHectares
Heather LakeWenatchee National Forest2.0%86.67
South RidgeOkanogan National Forest1.9%47.07
Norse PeakMt Baker-Snoqualmie National Forest1.8%67.5
Norse PeakWenatchee National Forest1.7%71.64
Hidden LakeMt Baker-Snoqualmie National Forest1.1%28.35
Long SwampOkanogan National Forest0.9%247.14
Glacier Peak BMt Baker-Snoqualmie National Forest0.9%67.68
Eagle RockMt Baker-Snoqualmie National Forest0.5%65.61
Mt. Baker Noisy - DiobsudMt Baker-Snoqualmie National Forest0.5%104.85
TeanawayWenatchee National Forest0.4%130.14
Dark DivideGifford Pinchot National Forest0.4%78.93
SawtoothOkanogan National Forest0.4%175.5
Methodology and Data Sources

Ecosystem classification: Ecosystems are classified using the LANDFIRE 2024 Existing Vegetation Type (EVT) layer, mapped to NatureServe Terrestrial Ecological Systems via a curated crosswalk. Each EVT is linked to the USNVC (U.S. National Vegetation Classification) hierarchy through pixel-level co-occurrence analysis of LANDFIRE EVT and NatureServe IVC Group rasters across all roadless areas.

Vegetation coverage: Coverage percentages and hectares are derived from zonal statistics of the LANDFIRE 2024 EVT raster intersected with roadless area boundaries.

Ecosystem narratives and community species: Sourced from the NatureServe Explorer API, representing professional ecological assessments of vegetation composition, environmental setting, dynamics, threats, and characteristic species assemblages.

IVC hierarchy: The International Vegetation Classification hierarchy is sourced from the USNVC v3.0 Catalog, providing the full classification from Biome through Association levels.

Component associations: Plant community associations listed as components of each NatureServe Ecological System. Association data from the NatureServe Explorer API.

State ranks: Conservation status ranks assigned by NatureServe member programs in each state where the ecosystem occurs.