Note: This website is no longer being updated and is being maintained for archive purposes by the Department of Botany, National Museum of Natural History, Smithsonian Institution. Please see About the Project for further details.

Link to North America map of regional study sites
North America map

Link to Middle America map
Middle America map

Link to South America
South America map

Link to Centres of Plant Diversity home page

Link to Smithsonian Institution

Link to Department of Botany, National Museum of Natural History


Link to North America Regional Overview
North America Regional Centre of Endemism: CPD Site NA16c

California and Oregon, U.S.A.

Location: South-western Oregon and north-western California at latitudes c. 41°-43°N and longitudes 121°-124°W.
55,000 kmē.
600-2280 m. Highest peak is Mount Ashland in Oregon.
Mixed evergreen, montane and subalpine forests; also serpentine vegetation, redwood forest and other types
A rich flora, estimated 3500 vascular plant species, with representatives of many floristic elements; nearly 280 endemic taxa, but few palaeoendemics.
Useful plants:
Timber species, medicinal species (e.g. Taxus brevifolia), craft and horticultural species.
Other values:
Scenery, wilderness experience, white-water boating.
Logging, mining, agriculture and grazing; potentially hydroelectric dams.
Large areas designated Wilderness Areas (although mining permitted); small areas of selected habitats protected by Federal Research Natural Area Program.

Map 4: CPD Site NA16


The Klamath-Siskiyou region of south-western Oregon and north-western California is an area of old and geologically complex mountains (see Map 4, California Floristic Province Data Sheet NA16). It forms a bridge between the Cascade-Sierra axis and the Pacific Ocean, and also bridges the Coast ranges of Oregon and California. It covers an area of 55,000 kmē (Smith and Sawyer 1988). The land surface rose above sea-level in the Mesozoic, mainly as islands, but then as part of the continental land mass (since the beginning of the Tertiary). The Coast ranges to the north and south are much younger and the volcanoes of the Cascades only a few million years old, or less.

The topography is rugged, with numerous fault systems. Elevation ranges from 600 m in the western portion to as high as 2280 m at Mount Ashland (Oregon). The main rivers are the Rogue and Klamath rivers. The oldest rocks are schists, presumably originating in the Palaeozoic (but their exact age is uncertain due to faulting and extensive metamorphosis in the late Jurassic). Thick beds of metasedimentary and volcanic rocks are of Triassic age. Granitic intrusions and folding occurred during the Nevadan Orogeny in the late Jurassic-early Cretaceous. It was preceded by intrusions of pyroxenite and peridotite which have been altered to various serpentine minerals. Deposits of sedimentary and volcanic rocks were emplaced at later times. Being the leading point of a continental plate, compression, folding, uplift and erosion have continuously affected the region.

The Klamath region is still affected by earth movements today. As a result of the complex geological history, a mosaic of parent materials is concentrated in a relatively small area, giving rise to a variety of soil types.

The climate of the region is Mediterranean, that is with mild, moist winters and a period of drought in the summer. Near the coast, annual precipitation may exceed 2500 mm, while in interior valleys it can be less than 250 mm.

Frosts at any time are rare at low altitudes in the southern part of the region; the summit areas of higher peaks receive enough snow in the winter to support ski facilities. Severe storms with high winds almost never occur.

Return to Top


The Klamath-Siskiyou region is notable for its complex mosaic of vegetation types. It represents the contact between the Pacific Northwest Floristic Province and the Californian Province. In addition to a mixing of formations from the north and south, it contains a substantial complement of elements from the east. The presence of extensive deposits of serpentine substrates adds much to the complexity of vegetation patterns. The classic treatment of the vegetation of the area is that of Whittaker (1960) which describes three main types of vegetation on normal soils:

1. Mixed evergreen forests: These occur at lower elevations, inland from the coast. The only ubiquitous conifer is Pseudotsuga menziesii, while Chamaecyparis lawsoniana and Pinus spp. are frequent. The type is characterized by prominence of evergreen hardwood trees, Arbutus, Lithocarpus, Castanopsis, Umbellularia and Quercus spp. being typical. Other broadleaved trees, such as Acer macrophyllum and Alnus rubra, are equally widespread on more mesic sites (Sawyer, Thornburgh and Griffin 1977). Mixed hardwood forests and oak woodlands occur along the southern fringe of the region.

2. Montane forests: Above 600-1300 m are conifer-dominated forests best defined by the presence of Abies concolor (Sawyer and Thornburgh 1977). Pseudotsuga, Pinus spp. and Chamaecyparis are prominent, as well as Calocedrus. Evergreen hardwoods are found at lower altitudes. The shrub and herb layer is rich in species. Extensive shrub fields are common on drier sites.

3. Subalpine forests: Above 1400 m there are three forest zones dominated by various conifers. The lowest is dominated by Abies magnifica or A. procera, the next by Tsuga mertensiana and the highest by Pinus albicaulis. Open meadows are found at sites where soils are too thin to support trees. The upper tree-line is defined by edaphic, rather than climatic, limits.

Serpentine soils support a distinctive vegetation, which is usually quite sparse, with the trees widely spaced and much bare ground exposed. Within these areas are pine woodlands (Pinus jeffreyi) at lower elevations, a forest-shrub complex with Pseudotsuga, Chamaecyparis lawsoniana and Pinus monticola, and subalpine communities with Pinus balfouriana (Whittaker 1960; Sawyer and Thornburgh 1977).

The Klamath-Siskiyou region, as defined here, also includes a portion of the magnificent redwood forest near the coast (Zinke 1977), coastal prairie and coastal scrub (Franklin and Dyrness 1973; Heady et al. 1977), Interior Valley grasslands (Franklin and Dyrness 1973), as well as fragments of typical forests of the Tsuga heterophylla zone (Franklin and Dyrness 1973) and Californian chapparal (Hanes 1977).

Return to Top


Although several botanists had visited the area earlier, the exploration of Thomas Jefferson Howell in the latter part of the 19th Century first brought to light the richness of the endemic flora of the region. He found the serpentine region around Waldo, in south-western Oregon, to be particularly rich and many new discoveries were made there. The endemic flora has recently been enumerated by Smith and Sawyer (1988). Their paper lists nearly 280 endemic taxa, many of which are infraspecific taxa. Although there are a number of species which can be considered relicts - Picea breweriana and Kalmiopsis leachiana are the best known examples - most of the endemic taxa are not palaeoendemics. Endemism above the rank of species is limited, the monotypic Bensoniella and Tracyina being the only endemic genera. Smith and Sawyer (1988) contend that the high degree of endemism at the infraspecific level reflects a pattern of recent diversification of the flora into the region's heterogeneous habitats. The open habitats of serpentine materials are particularly rich in endemics.

The area has served as a refugium for species that moved into the area in the past and which have been stranded in small sites of favourable relief and climate. The diversity of relictual species in such refugia is notable. For example there may be as many as 12 different species of conifers in one small valley (D. Axelrod, pers. comm.). At various times in the past, beginning early in the Tertiary, when the climate was warmer or cooler, wetter or drier, species moved into the area. They have come from all directions and now occur mixed together in complex plant communities. For this reason, Whittaker (1961) suggested that the area has a "central" significance.

There is no floristic treatment that covers the whole region well. The California portion of the region is covered by the new Jepson Manual (Hickman 1993), and is estimated to contain over 3500 taxa of vascular plants (Smith and Sawyer 1988). The most useful references for the area north of the California border, in addition to the Jepson Manual, are Abrams and Ferris (1923-1960), Munz and Keck (1959), Munz (1968) and Peck (1961).

Return to Top

Useful plants

The region, as much of the Pacific Northwest, has been a major source of timber. As the more productive forests further to the north have begun to show signs of being depleted, pressure on logging in the Klamath area has increased. The old-growth forests near the coast, in particular, have been extensively logged during the 1960s-1990s. Decorative foliage is a significant product; boughs for Christmas wreaths are exported to Europe. The bark of the western yew, Taxus brevifolia, is being stripped at a rapid rate for the production of taxol, a new anti-cancer drug of great promise. There is an annual harvest of beargrass (Xerophyllum tenax) by native Americans for trade. It is used to make fine baskets. Commercial mushroom picking has increased dramatically in recent years. Grasslands have value as livestock forage; grazing permits are issued in suitable areas. Many species are of horticultural value; several nurseries specialize in rare plants of the area.

Return to Top

Social and environmental values

As there are no roads throughout much of the region, its remoteness provides significant amounts of land for people seeking wilderness experiences. The Rogue and Klamath rivers are famous for spectacular scenery and exciting white water, and are used for kayak, canoe and rafting expeditions. The pressure is so intense that a permit system is in effect on both of these rivers during the most popular months. Other forms of outdoor recreation are practised extensively.

Economic assessment

The bulk of revenue generated from forestry comes from four forests in the area. In fiscal year 1990, nearly US$80,000,000 was received from cut timber. The Bureau of Land Management also manages forests in the area, but data are not available. Lesser amounts (less than $50,000 per item per forest) are received from grazing fees, campground fees, power generation, land use fees, mineral leases and other recreation fees. Mining has also been an important activity in the area.

Return to Top


Old-growth stands of trees have been much reduced in extent, with most outside the Wilderness Areas or parks scheduled for clear-cutting. Placer mining has disturbed many of the valley gravel deposits in the past. There are plans for utilizing the weathered soils for extraction of chromium and other rare metals; this process could have significant impacts on large areas, since only the overburden is desired. Over-collecting by commercial plant dealers has reduced some populations of rare plants. Road building has had a similar effect on the periphery of the area. Off-road vehicles damage open slopes where the substrate is unstable. Agriculture and urbanization has eliminated almost all of the valley bottom grasslands, while the grassy areas on hillsides are grazed by livestock. Many of the watersheds on the eastern side of the region, especially in their upper reaches, have been severely impacted by nearly a century of overgrazing. There is pressure to develop the hydroelectric potential of some of the rivers. Conflicts have led to halting construction on a partially completed dam in Oregon.

Return to Top


Much of the area is protected by its remoteness and the rugged nature of the terrain. Large areas have been designated Wilderness Areas (although mining is still permitted in such areas). The central and western Siskiyous of Oregon are within the Siskiyou National Forest and the eastern Siskiyous in the Rogue River National Forest (Whittaker 1960). Extensive Wilderness Areas have been set aside in the Yolla Bolly (2891 ha), Salmon and Trinity Alps (1871 ha), and the Marble Mountains (97,831 ha) (IUCN 1992); and small areas of the coastal redwood forests are protected as parks. Several conservation groups have proposed a Siskiyou National Park, but the likelihood of this proposal being implemented seems remote at present. The federal Endangered Species Act is having significant impact on conservation, especially in areas that are classified as old-growth forests. Both Oregon and California have state endangered species legislation. Oregon has very strong land use laws that specify conservation of natural values, although they are not always carefully enforced in the less-populated counties. The Federal Research Natural Area Program is important for protecting small areas of selected habitats. State programs are less successful in this area; private groups such as The Nature Conservancy are more effective. Conservation organizations such as the Sierra Club, the Audubon Society, the Wilderness Society and the Oregon Natural Resources Council are important for promoting conservation issues in the political arena.

Return to Top

Map 4. California Floristic Province, U.S.A. and Mexico (CPD Site NA16)

Return to Top


Abrams, L. and Ferris, R.S. (1923-1960). Illustrated flora of the Pacific states. Vols. 1-4. Stanford University Press, Stanford.

Franklin, J.F. and Dyrness, C.T. (1973). Natural vegetation of Oregon and Washington. USDA Forest Service Gen. Tech. Rep. PNW-80. Portland.

Hanes, T.L. (1977). California chaparral. In Barbour, M.G. and Major, J. (eds), Terrestrial vegetation of California. John Wiley and Sons, New York. Pp. 417-469.

Heady, H.F., Foin, T.C., Hektner, M.M., Taylor, D.W., Barbour, M.B. and James Barry, W. (1977). Coastal prairie and northern coastal scrub. In Barbour, M.G. and Major, J. (eds), Terrestrial vegetation of California. John Wiley and Sons, New York. Pp. 733-760.

Hickman, J. (ed.) 1993. The Jepson manual: higher plants of California. University of California Press, Berkeley. 1400 pp.

IUCN (1992). Protected areas of the world. A review of national systems. Vol. 4: Nearctic and Neotropical. IUCN, Gland, Switzerland and Cambridge, U.K. (Compiled by the World Conservation Monitoring Centre.) 459 pp.

Munz, P.A. (1968). Supplement to a California flora. University of California Press, Berkeley. 224 pp.

Munz, P.A. and Keck, D.D. (1959). A California flora. University of California Press, Berkeley. 1681 pp.

Peck, M.E. (1961). A manual of the higher plants of Oregon. 2nd ed. Binsford and Mort, Portland.

Sawyer, J.O. and Thornburgh, D.A. (1977). Montane and subalpine vegetation of the Klamath Mountains. In Barbour, M.G. and Major, J. (eds), Terrestrial vegetation of California. John Wiley and Sons, New York. Pp. 699-732.

Sawyer, J.O., Thornburgh, D.A. and Griffin, J.R. (1977). Mixed evergreen forest. In Barbour, M.G. and Major, J. (eds), Terrestrial vegetation of California. John Wiley and Sons, New York. Pp. 359-381.

Smith, J.P. and Sawyer, J.O. Jr. (1988). Endemic vascular plants of northwestern California and southwestern Oregon. Madroņo 35(1): 54-69.

Whittaker, R.H. (1960). Vegetation of the Siskiyou Mountains, Oregon and California. Ecological Monographs 30(3): 279-338.

Whittaker, R.H. (1961). Vegetation history of the Pacific coast states and the "central" significance of the Klamath region. Madroņo 16(1): 5-23.

Zinke, P.J. (1977). The redwood forest and associated north coast forests. In Barbour, M.G. and Major, J. (eds), Terrestrial vegetation of California. John Wiley and Sons, New York. Pp. 679-698.


This Data Sheet was written by Dr David H. Wagner (Northwest Botanical Institute, P.O. Box 30064, Eugene, Oregon 97403, U.S.A.).

Return to Top

North | Middle | South

CPD Home  

Botany Home Page  | Smithsonian Home