Tanoak grows within the life zones classified as the Canadian and  Transition. It is the most abundant hardwood species in timber  stands of the Coast Ranges of California (6) and southwestern  Oregon. Tanoak is a common component in the following forest  cover types (4): Redwood (Society of American Foresters Type  232), Pacific Ponderosa Pine (Type 245), Pacific Ponderosa  Pine-Douglas-Fir (Type 244), Sierra Nevada Mixed Conifer (Type  243), and California Coast Live Oak (Type 255). It is a  particularly important component of Pacific Douglas-Fir (Type  229) and Douglas-Fir-Tanoak-Pacific Madrone (Type 234).

   

The principal body of tanoak is a broad band along the inland side  of the redwood belt. Here tanoak sometimes forms almost pure  stands (6). More often it is an understory tree with Douglas-fir  or is a component of hardwood stands or mixed hardwood-conifer  forests. The most common hardwood associated with tanoak is  Pacific madrone. Other frequent hardwood associates include giant  chinkapin (Castanopsis chrysophylla), canyon live oak  (Quercus chrysolepis), California black oak Q.  kelloggii), and California-laurel (Umbellularia  californica). Tanoak is found most often with Douglas-fir and  redwood. Other common conifer associates are California white fir  (Abies concolor var. lowiana), Sitka spruce (Picea  sitchensis), sugar pine (Pinus lambertiana), ponderosa  pine (P. ponderosa var. ponderosa), California  torreya (nutmeg) (Torreya californica), and western  hemlock (Tsuga heterophyl1a).

   

A large variety of shrubs, forbs, grasses, sedges, and ferns are  also associated with tanoak. Generally these plants are not  abundant on forested land, but, with tanoak sprouts, often become  aggressive on burned or cutover areas. Among the most common  shrubs are blueblossom (Ceanothus thyrsiflorus), California  hazel (Corylus cornuta var. californica), salal  (Gaultheria shallon), Pacific bayberry (Myrica  californica), Pacific rhododendron (Rhododendron  macrophyllum), flowering currant (Ribes sanguineum), thimbleberry  (Rubus parviflorus), western poison-oak (Toxicodendron  diversilobum), and California huckleberry (Vaccinium  ovatum).

   

Two smaller plants producing woody growth above ground are  prince's-pine (Chimaphila umbellata var. occidentalis)  and Oregon grape (Berberis nervosa). Many forbs and  grasses are plentiful in the tanoak range. Among the most  important forbs are bull thistle (Cirsium vulgare), New  Zealand fireweed (Erechtites arguta), Australian fireweed  (E. minima), and western whipplea (Whipplea modesta).  Common grass species include California brome (Bromus  carinatus), soft chess (B. mollis), California fescue  (Festuca californica), and California sweetgrass (Hierochloe  occidentalis). Western swordfern (Polystichum munitum)  and western bracken (Pteridium aquilinum var. pubescens)  sometimes grow abundantly with tanoak. Sedges (Carex  spp.) also are represented in some places.