Alnus rhombifolia Forest & Woodland Alliance
White alder groves

USDA Ecological Section Map

Summary Information

  • Primary Life FormTree
  • Elevation0-2500 m
  • State RarityS4
  • Global RarityG4
  • DistributionUSA: CA, ID, OR, WA, WY. Mexico (NatureServe)
  • Endemic to CaliforniaNo
  • Endemic to California Floristic Province and DesertsNo
  • Date Added1995/11/01

Characteristic Species

Alnus rhombifolia is dominant or co-dominant in the tree canopy with Acer macrophyllum, Chamaecyparis lawsoniana, Fraxinus latifolia, Notholithocarpus densiflorus, Platanus racemosa, Populus fremontii, Populus trichocarpa, Pseudotsuga menziesii, Quercus lobata and Salix spp.

Vegetation Layers

Trees < 35 m; canopy is open to continuous; it may be two tiered. Shrub layer is sparse to continuous. Herbaceous layer is variable.

Membership Rules

  • Alnus rhombifolia > 30% relative cover in the tree canopy (Klein et al. 2007).
  • Alnus rhombifolia > 5% absolute cover in the tree canopy; dominant plants are mature trees (Potter 2005).
  • Alnus rhombifolia > 50% relative cover in the tree canopy; it does not co-dominate with conifers. (Keeler-Wolf et al. 2003b).
  • Alnus rhombifolia comprises > 10% absolute cover in the tree canopy; Salix cover in the understory may be significantly higher than A. rhombifolia but Quercus lobata < 5% cover (Keeler-Wolf et al. 2003a).


Riparian corridors, incised canyons, seeps, stream banks, mid-channel bars, floodplains, and terraces. The USFWS Wetland Inventory (1996 national list) recognizes Alnus rhombifolia as a FACW plant.

Other Habitat, Alliance and Community Groupings

MCV (1995) White alder series
NVCS (2009) Alnus rhombifolia temporarily flooded forest alliance
Calveg Riparian mixed shrub, White alder
Holland White alder riparian forest, Southern sycamore-alder riparian woodland
Munz Foothill woodland
WHR Montane riparian
CDFW CA Code 61.420.00

National Vegetation Classification Hierarchy

Formation Class Mesomorphic Tree Vegetation (Forest and Woodland)
Formation Subclass Temperate Forest
Formation Temperate Flooded and Swamp Forest
Division Western North America Flooded and Swamp Forest
Macro Group Western Cordilleran montane-boreal riparian scrub
Group Vancouverian riparian deciduous forest