Tsuga heterophylla Forest Alliance
Western hemlock forest

USDA Ecological Section Map

Summary Information

  • Primary Life FormTree
  • Elevation10-400 m
  • State RarityS2
  • Global RarityG5
  • DistributionCAN: BC. USA: CA, OR, WA (NatureServe)
  • Endemic to CaliforniaNo
  • Endemic to California Floristic Province and DesertsNo
  • Date Added1995/11/01

Characteristic Species

Tsuga heterophylla is dominant or co-dominant in the tree canopy with Arbutus menziesii, Chamaecyparis lawsoniana, Notholithocarpus densiflorus, Pseudotsuga menziesii, Sequoia sempervirens and Umbellularia californica.

Vegetation Layers

Trees < 60 m tall; canopy is continuous. Shrub layer is open to intermittent. Herbaceous layer is sparse or abundant.

Membership Rules

  • Tsuga heterophylla > 50% relative cover, or with Pseudotsuga menziesii and T. heterophylla > 25% relative cover in the tree canopy (NatureServe 2007).


Raised stream benches, terraces, and lower slopes.

Other Habitat, Alliance and Community Groupings

MCV (1995) Western hemlock series
NVCS (2009) Pseudotsuga menziesii-Tsuga heterophylla forest alliance
Calveg Pacific Douglas-fir
Holland Western hemlock forest, Coastal Douglas-fir-western hemlock forest
Munz Douglas fir forest
WHR Douglas fir
CDFW CA Code 84.200.00

National Vegetation Classification Hierarchy

Formation Class Mesomorphic Tree Vegetation (Forest and Woodland)
Formation Subclass Temperate Forest
Formation Cool Temperate Forest
Division Western North America Cool Temperate Forest
Macro Group Vancouverian Rainforest
Group Vancouverian hypermaritime lowland rainforest