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A0306 Alnus rhombifolia Cascadian Riparian Woodland Alliance

Type Concept Sentence: The upper canopy is dominated by Alnus rhombifolia. This alliance is found along riparian areas and habitats include narrow ravines and draws of coast and interior valleys of the Columbia River of Oregon and Washington, the Snake and Salmon river canyons of Idaho, south into tributaries of central and eastern Oregon, and into the west side of the Cascade Range and eastern side of the Coast Ranges.

Common (Translated Scientific) Name: White Alder Cascadian Riparian Woodland Alliance

Colloquial Name: Cascadian Riparian White Alder Woodland

Hierarchy Level:  Alliance

Type Concept: This alliance is found along riparian areas where the upper canopy is dominated by Alnus rhombifolia. Few other trees except for conifers from neighboring upslopes may be included, such as Abies grandis. Stands often have a subcanopy shrub layer with Amelanchier alnifolia, Betula occidentalis, Celtis laevigata var. reticulata, Philadelphus lewisii, Prunus virginiana, Rosa woodsii, and Sambucus nigra ssp. cerulea. It occurs in ravines and draws of the coastal and interior valleys of the Columbia River of Oregon and Washington, into the Snake and Salmon river canyons of Idaho, south into central and eastern Oregon, and into the west side of the Cascade Range and eastern side of the Coast Ranges. Elevation range is 100 to 1000 m (500-3280 feet), with a rough average of 500 to 800 m (1640-2624 feet).

Diagnostic Characteristics: Stands of Alnus rhombifolia within Washington, northern and central Oregon, and Idaho.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: This alliance contains the somewhat disjunct populations of Alnus rhombifolia found in Washington, Oregon and Idaho, which have distinct floristics from stands occurring in southwestern Oregon and California.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: The tree layer is dominated by broad-leaved deciduous trees (20-35 m tall) and/or with a mix of conifer trees. The canopy consists of trees with overlapping crowns, generally forming 60-100% cover. The shrub and forb layers are present; however, there was no percent cover given (Miller 1976).

Floristics: Vegetation of this alliance are dominated by Alnus rhombifolia. Some stands are dominated by a mix of Abies grandis with Alnus rhombifolia. Tree canopy cover is usually high, often with a dense, multi-layered, and diverse shrub layer, also primarily deciduous. In some cases, both the tree and shrub canopy can be sparse, but Alnus rhombifolia is always a dominant. Associated trees (usually more than isolated individuals) include Pseudotsuga menziesii, Pinus ponderosa, and Populus balsamifera ssp. trichocarpa. Shrub-layer dominants include Amelanchier alnifolia, Betula occidentalis, Celtis laevigata var. reticulata, Cornus sericea, Crataegus douglasii, Lonicera spp., Philadelphus lewisii, Prunus virginiana, Rosa woodsii, Salix scouleriana, Sambucus nigra ssp. cerulea (= Sambucus caerulea), Spiraea betulifolia, and Taxus brevifolia. The herb layer can be sparse or with high cover and includes such dominant species as Adenocaulon bicolor, Maianthemum stellatum, Polystichum munitum, Rubus parviflorus, and Trillium ovatum.

Dynamics:  Stands appear to thrive when disturbed by periodic flooding, mud and rock flows, and moderate fluvial disturbance to create canopy gaps and diverse floodplain substrates (Miller 1976). Lack of disturbance will allow the more shade-tolerant species to dominate the stand to the exclusion of Alnus rhombifolia.
Environmental Description:  Elevation ranges from subalpine over 2740 m to canyon bottoms below 600 m. Topography is characterized by precipitous canyon walls along the rivers, steep upland slopes, and smaller tributary streams with cliffs, rocky slopes and mass-wasting features such as slumps and mud-rock flows. The soils of this region are especially prone to erosion and slippage. Slopes often exceed the angle of repose and periodic severe thunderstorms with intense rains will supersaturate the soil mantle. The resulting slumping and mud-rock flows often deposit materials into stream channels and can collapse streambanks. This alliance occurs on riparian sites in canyon bottoms, from 385 m to 640 m elevation along the Snake River tributaries, and from 550 m to 760 m along the Salmon River tributaries. The climatic conditions in these deep canyon bottoms are strikingly different from surrounding uplands and mountains with cold-air drainage and stable canyon-bottom water tables. Soils are alluvial with regular disturbance from flooding, and stands are generally within 5 m of flowing water.
Geographic Range: This alliance occurs along the Columbia River corridor, central and eastern Oregon, river canyons of western Idaho, and southern Washington.

Nations: US

States/Provinces:  CA, ID, OR, WA


Confidence Level: Low

Confidence Level Comments: No Data Available
Grank: GNR

Greasons: No Data Available
Type Name Database Code Classification Code
Class 1 Forest & Woodland Class C01 1
Subclass 1.B Temperate & Boreal Forest & Woodland Subclass S15 1.B
Formation 1.B.3 Temperate Flooded & Swamp Forest Formation F026 1.B.3
Division 1.B.3.Ng Vancouverian Flooded & Swamp Forest Division D193 1.B.3.Ng
Macrogroup 1.B.3.Ng.1 Vancouverian Flooded & Swamp Forest Macrogroup M035 1.B.3.Ng.1
Group 1.B.3.Ng.1.b Mountain Hemlock - Fir species / Willow species Montane Riparian Woodland Group G507 1.B.3.Ng.1.b
Alliance A0306 White Alder Cascadian Riparian Woodland Alliance A0306 1.B.3.Ng.1.b
Association CEGL000630 White Alder - Grand Fir Riparian Forest CEGL000630 1.B.3.Ng.1.b
Association CEGL000631 White Alder / Saskatoon Serviceberry Riparian Forest CEGL000631 1.B.3.Ng.1.b
Association CEGL000632 White Alder / Water Birch Riparian Forest CEGL000632 1.B.3.Ng.1.b
Association CEGL000633 White Alder / Netleaf Hackberry Riparian Forest CEGL000633 1.B.3.Ng.1.b
Association CEGL000634 White Alder / Lewis'' Mock Orange Riparian Forest CEGL000634 1.B.3.Ng.1.b
Association CEGL000635 White Alder / Chokecherry Riparian Forest CEGL000635 1.B.3.Ng.1.b
Association CEGL000636 White Alder / Woods'' Rose Riparian Forest CEGL000636 1.B.3.Ng.1.b
Association CEGL000637 White Alder / Blue Elderberry Riparian Forest CEGL000637 1.B.3.Ng.1.b
Concept Lineage: A.306, in part

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: No Data Available
Concept Author(s): G. Kittel, in Faber-Langendoen et al. (2013)

Author of Description: G. Kittel

Acknowledgements: No Data Available

Version Date: 12-18-14
  • Burns, R. M., and B. H. Honkala, technical coordinators. 1990a. Silvics of North America: Volume 1. Conifers. Agriculture Handbook 654. USDA Forest Service, Washington, DC. 675 pp.
  • Faber-Langendoen, D., J. Drake, M. Hall, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, M. Russo, K. Schulz, L. Sneddon, K. Snow, and J. Teague. 2013-2019b. Screening alliances for induction into the U.S. National Vegetation Classification: Part 1 - Alliance concept review. NatureServe, Arlington, VA.
  • Johnson, F. D. 1968. Taxonomy and distribution of northwestern alders. Pages 9-22 in: J. M. Trappe, J. F. Franklin, R. F. Tarrant, and G. M. Hansen, editors. Biology of Alder. Pacific Northwest Forest and Range Experimental Station, Portland, OR.
  • Miller, T. B. 1976. Ecology of riparian communities dominated by white alder in western Idaho. Unpublished thesis, University of Idaho, Moscow. 154 pp.
  • Reid, M. S., L. S. Engelking, and P. S. Bourgeron. 1994. Rare plant communities of the conterminous United States, Western Region. Pages 305-620 in: D. H. Grossman, K. L. Goodin, and C. L. Reuss, editors. Rare plant communities of the conterminous United States, an initial survey. The Nature Conservancy, Arlington, VA.