Print Report

A0104 Chamaecyparis lawsoniana Forest Alliance

Type Concept Sentence: This coniferous forest alliance consists of mixed conifer forests dominated by Chamaecyparis lawsoniana in the tree canopy. Pseudotsuga menziesii is common in most stands, and additional codominants include Tsuga heterophylla and Picea sitchensis. This alliance occurs in a very restricted range in the Klamath-Siskiyou mountain region of northern California and southern Oregon.


Common (Translated Scientific) Name: Port Orford-cedar Forest Alliance

Colloquial Name: Port Orford-cedar Forest

Hierarchy Level:  Alliance

Type Concept: This coniferous forest alliance is dominated by Chamaecyparis lawsoniana, usually codominated with other tree species such as Abies lowiana, Abies magnifica, Callitropsis nootkatensis, Picea breweriana, Picea sitchensis, Pseudotsuga menziesii, Taxus brevifolia, and Tsuga heterophylla. Other trees that may be present are broad-leaved tree species such as Acer macrophyllum, Alnus rubra, Chrysolepis chrysophylla, and Notholithocarpus densiflorus. The tall-shrub stratum can be dominated by Acer circinatum, Gaultheria shallon, Rhododendron macrophyllum, or Vaccinium parvifolium. Shorter shrubs may include Chimaphila umbellata, Leucothoe davisiae, Mahonia nervosa, Paxistima myrsinites, Rosa gymnocarpa, Rubus ursinus, or Vaccinium membranaceum. Herbaceous layers commonly have shade-tolerant species such as Clintonia uniflora, Goodyera oblongifolia, Linnaea borealis, Oxalis oregana, and Polystichum munitum. This alliance has a restricted range in the Klamath-Siskiyou mountain region of northern California and southern Oregon, but shows wide ecological amplitude within that range.

Diagnostic Characteristics: Upland (non-flooded) stands dominated by Chamaecyparis lawsoniana.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: Often a mix of several trees, the extremely limited range of Chamaecyparis lawsoniana makes it difficult to place, and it seems housed best with its adjacent redwoods.

Similar NVC Types: No Data Available
note: No Data Available

Physiognomy and Structure: Vegetation within this alliance typically has a canopy of evergreen, scale-leaved trees of moderate to high density and high (60-100%) cover. This canopy can be over 50 m in height in some stands. Cold-deciduous or sclerophyllous broad-leaved trees commonly form a subcanopy. On serpentine soils, these forests grade into woodlands with irregular canopy closure. The understory usually contains a layer of tall (2-5 m tall), ericaceous shrubs of moderate (25-60%) cover and a short-shrub layer (0.5-2 m tall) with 10-40% cover. The herbaceous understory is typically a dense layer of shade-tolerant ferns and forbs.

Floristics: Despite the small range of Chamaecyparis lawsoniana, vegetation within this alliance is diverse. In the northern portion of its range, Chamaecyparis lawsoniana grows with Tsuga heterophylla, and in coastal stands with Picea sitchensis. Pseudotsuga menziesii is common, or codominant, in most stands. Other conifers that may be found include Abies lowiana (= Abies concolor var. lowiana), Abies magnifica, Callitropsis nootkatensis (= Chamaecyparis nootkatensis), Picea breweriana, and Taxus brevifolia. The northern stands lie north of the Rogue River, Oregon, and are the most extensive, continuous, and productive forests within this alliance. Understories are somewhat typical of the coastal forests of central Oregon, often with a broad-leaved tree subcanopy of Acer macrophyllum, Alnus rubra, Chrysolepis chrysophylla (= Castanopsis chrysophylla), or Notholithocarpus densiflorus (= Lithocarpus densiflorus), and a tall-shrub stratum of Acer circinatum, Gaultheria shallon, Rhododendron macrophyllum, or Vaccinium parvifolium. Shorter shrubs that can be common include Chimaphila umbellata, Leucothoe davisiae, Mahonia nervosa, Paxistima myrsinites, Rosa gymnocarpa, Rubus ursinus, or Vaccinium membranaceum. Herbaceous layers commonly have shade-tolerant species such as Clintonia uniflora, Goodyera oblongifolia, Linnaea borealis, Oxalis oregana, and Polystichum munitum.

South of the Rogue River, stands become more scattered and extend into the interior to become important components of the mixed evergreen and montane forests of the Klamath-Siskiyou mountains. In the mixed evergreen forests, Arbutus menziesii, Calocedrus decurrens, Notholithocarpus densiflorus, Pseudotsuga menziesii, and Umbellularia californica are common in the tree canopy, and ericaceous and other shrubs, such as Quercus sadleriana, Quercus vacciniifolia, and Morella californica (= Myrica californica), may be abundant. Important herbs may include Xerophyllum tenax, in addition to the species above.

Dynamics:  Chamaecyparis lawsoniana is a somewhat shade-tolerant conifer. It regenerates under its own shade and will eventually dominate stands where it co-occurs with Pinus spp., if disturbance is absent. Conversely, it appears to be less shade-tolerant and much more fire-tolerant than Tsuga heterophylla or Picea sitchensis, and can vigorously colonize recently burned substrates. Mature individuals of Chamaecyparis lawsoniana have thick, fire-resistant bark which allows them to persist through repeated fires. Phytophthora root rot, a water-borne disease spread by logging and other anthropogenic disturbances, is severely impacting stands of this alliance throughout its range. Many stands have been lost to this pathogen and populations are presently in decline throughout the range of the species.

Environmental Description:  This alliance occurs in a very narrow geographic area within the Klamath-Siskiyou mountains, but shows wide ecological amplitude within that range. Most of this area is strongly influenced by maritime air and lies at the northern cusp of the Mediterranean climate region of the Pacific coast. Winters are cool and wet; summers are warm and dry. Annual precipitation ranges from 100-225 cm, with only 2-4% falling between June and August (Burns and Honkala 1990a). Stands of this alliance are usually associated with penetration of ocean fog, and are particularly well-developed on moist toeslopes and valley bottoms of coastal river drainages. Disjunct inland stands occur at up to 2000 m elevation in the southern Cascades and inner Klamath Mountains; stands become increasingly dependent upon moist, topographically protected microhabitats in the interior, often in association with streams or springs.

Geologically, this region is very complex and of very old deposits. Rock types include volcanic tuffs and sedimentary rocks which have been metamorphosed into schists, gneisses, marbles, and other metavolcanic and metasedimentary rocks. Although communities within this alliance occur on a variety of soil types, they are particularly abundant on moist ultramafic soils with perched water tables. These soils are often derived from alluvium or colluvium and are typically coarse in texture. Adjacent vegetation is varied, from Picea sitchensis, Abies grandis, or Tsuga heterophylla forests near the coast, to Abies lowiana, Abies magnifica, or Calocedrus decurrens forests in high-elevation interior stands, to Pinus jeffreyi or Pinus monticola forests on serpentine soils.

Geographic Range: Vegetation types within this alliance are restricted to the Klamath-Siskiyou mountains region of northwestern California and southwestern Oregon. The northern and southern extremes are the Coos Bay region of Oregon and the Mad River drainage of Humboldt County, California. The range is fairly continuous near the coast, but becomes more scattered in the interior. A large disjunct distribution occurs in the southeastern Trinity Mountains southwest of Mount Shasta, California.

Nations: US

States/Provinces:  CA, OR




Confidence Level: Moderate

Confidence Level Comments: No Data Available

Grank: G3

Greasons: No Data Available


Concept Lineage: No Data Available

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available

Synonomy: = Chamaecyparis lawsoniana (Port Orford cedar forest) Alliance (Sawyer et al. 2009) [81.100.00]
= Chamaecyparis lawsoniana Forest Alliance (CNPS 2017) [81.100.00]
= Port Orford cedar series (Sawyer and Keeler-Wolf 1995)
>< Port Orford-Cedar: 231 (Eyre 1980)
= Port-Orford-Cedar Forest (#82500) (Holland 1986b)

Concept Author(s): M.S. Reid and D. Sarr, in Faber-Langendoen et al. (2013)

Author of Description: G. Kittel

Acknowledgements: No Data Available

Version Date: 09-26-14

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