Common (Translated Scientific) Name: Tanoak - Pacific Madrone Forest Alliance

Colloquial Name: Tanoak - Madrone Forest

Hierarchy Level:  Alliance

Type Concept: This alliance consists of forests dominated by Notholithocarpus densiflorus and/or Arbutus menziesii. Other tree species include Acer macrophyllum, Alnus rubra, Calocedrus decurrens, Chamaecyparis lawsoniana, Chrysolepis chrysophylla, Cornus nuttallii, Pinus coulteri, Pinus lambertiana, Pseudotsuga menziesii, Quercus agrifolia, Quercus chrysolepis, Quercus kelloggii, Sequoia sempervirens, Torreya californica, Tsuga heterophylla, and Umbellularia californica. Conifers are generally not abundant. Trees are <45 m in height and the canopy is continuous. The shrub layer is sparse to intermittent and the herbaceous layer is sparse. This alliance is found in the southern Cascades and Klamath Mountains of southern Oregon and into northern California, extending south into the northern California Coast Ranges, and northern and central coast of California. A few disjunct stands occur in the northern sections of the Sierra Nevada of California. Stands of Arbutus menziesii occur as far south as the southern California mountains and valleys in the Transverse and Peninsular ranges. Elevation ranges from 100-1500 m. Habitats include stream terraces and upland slopes with deep and well-drained productive soils or steep slopes with shallow, rocky, infertile soils.

Diagnostic Characteristics: Notholithocarpus densiflorus >50% relative cover and >10% absolute cover in the tree layer; present in the regeneration layer (Jimerson et al. 1996); or Arbutus menziesii >50% relative cover in tree canopy.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: From Sawyer et al. (2009): "Stands of this and other alliances with Lithocarpus densiflorus are often referred to as mixed evergreen forest (Sawyer 2006, 2007), but Bingham''s (1999) study found that stands with a dominance of Lithocarpus densiflorus segregated significantly in species composition and environmental conditions from others containing Lithocarpus densiflorus with other evergreens. Pseudotsuga menziesii is a small component of this alliance. Stands of the shrub form (var. echinoides) are placed in ~Western North American Montane Sclerophyll Scrub Group (G282)$$. Forest ecologists have used the name Lithocarpus densiflorus series or alliance to refer to stands that have a low presence of conifers such as Pseudotsuga menziesii or Sequoia sempervirens (e.g., Atzet and Wheeler 1982, Jimerson et al. 1996). We place such stands in the Pseudotsuga menziesii - Lithocarpus densiflorus or Sequoia sempervirens alliances.

"Arbutus menziesii groves usually are considered part of the mixed evergreen forest, and not treated as a separate type (Sawyer 2007). Even though the species is common as a secondary species in many forest types, it does form distinctive stands of high cover worthwhile of recognition. Arbutus menziesii stands are ecologically most similar to those of Umbellularia californica. They tend to segregate from Umbellularia californica stands by occurring on upper slopes and convexities, but they tend to occur in somewhat more mesic settings than do Quercus agrifolia stands."

Review with California ecologists whether Umbellularia californica associations belong in this group / alliance, or should remain in ~Californian Broadleaf Forest & Woodland Group (G195)$$. J. Evens (pers. comm. 2013): Both Notholithocarpus densiflorus and Arbutus menziesii stands are related to Umbellularia californica stands. Hard to see these two former hardwoods split out from the latter, but better placed here than in the oak/hardwood group.

Similar NVC Types: No Data Available

note: No Data Available