Why is the Flora of California So Diverse? John Willoughby G.L. Stebbins and J. Major. 1965. Ecological Monographs 35: 1‐35. P. H. Raven and D.I. Axelrod. 1978. University of California Publications in Botany 72: 1‐ 134. California Department of Fish and Game. 2003. D.D. Ackerly. 2009. Journal of Biogeography 36: 1221‐1223. The California Floristic Province is essentially the area in which a Mediterranean climate prevails. It includes some of southwestern Oregon and northwestern Baja California. I’ll be talking about both California as a whole and about the California Floristic Province. Geology of California California is in the process of describing and naming its vegetation types. When this process is complete, it is likely that California will have over 2,000 distinct types of plant associations. This is almost half of the currently identified number of associations in the entire U.S. Evolution of California’s flora • California’s flora consists primarily of components of two major Tertiary floras: – Arcto‐Tertiary Geoflora: Conifers and broadleaf plants once existed together in a nearly contiguous belt across North America and Eurasia. – Madro‐Tertiary Geoflora: Mostly sclerophyllous plants that began expanding their range during the cooling and drying period of the mid‐Tertiary. Evolution of California’s flora • Significant remnants of the Tertiary geoflora remain in parts of California that did not experience harsh climatic conditions during past geologic periods. • For example, many areas of California did not experience the Pleistocene glaciation that occurred throughout much of the area covered by Gray’s Manual. California Endemic Plant Species • As of 2003 there were 6,272 plant taxa (species and infraspecific taxa) recorded for California (Atlas of the Biodiversity of California). • 2,153 of these taxa are endemic to California. • This represents an endemism rate of 34%. CFP Endemic Plant Species • 2,124 of the 3,488 species in the California Floristic Province are endemic. • This represents an endemism rate of 61%, a very high rate for an area that is not an island. The CFP as an island • Various authors have suggested that the CFP is like an island because there are physical barriers to dispersal of plant species into the CFP. • The CFP, like the other MT regions of the world, sits at the edge of a continent, surrounded by mountains. • Ackerly (2009) points out that the physical barriers afforded by mountains are not as effective as oceans over long time periods. The CFP as an island • Of more importance to the CFP functioning as an island is its Mediterranean climate. • Thus, even if propagules from outside the CFP somehow arrive, most will not be able to survive in the presence of a completely different environment. • Regions with distinctive environments promote ecological speciation among colonizing species similar to the speciation observed in islands. Types of Endemics • Paleoendemics: Relatively ancient species, often once of much wider distribution, that continue to exist only in California or the CFP. • Neoendemics: Species that have evolved in more recent times, many since the uplifting of the Sierra Nevada, Klamath, Coast, and Transverse ranges in the Pliocene epoch. • Edaphic endemics: Species that are endemic to a particular bedrock or soil type. Examples of Paleoendemics Sequoia sempervirens, coast redwood. Sequoiadendron giganteum, Sierra redwood, big tree Photo by Robert Potts Photo by Gerald and Buff Corsi Neoendemics • A large percentage of California’s neoendemics are annual dicots, such as members of the genera Amsinckia, Collinsia, Eriogonum, Lasthenia, Layia, Lupinus, and Mimulus. • Neoendemics can also be perennial or even woody species. Neoendemics • The following large families are noteworthy for their degree of endemism in California (Raven and Axelrod 1978): – Malvaceae (mallow family) 53.0% – Rhamnaceae (buckthorn family) 47.5% – Scrophulariaceae (figwort family) 41.1% * – Asteraceae (sunflower family) 51.6% * This family will no longer be “large” in Jepson Manual 2nd edition. Edaphic endemics • Most edaphic endemics are neoendemics. • Serpentine endemics (plants endemic to soils derived from ultramafic rocks) are the most famous and probably most numerous. • Other species are endemic to soils derived from carbonate, granitic, or volcanic rocks. Vernal pool endemics • Vernal pools are seasonal wetlands that form in depressions in the soil surface that are underlain by an impermeable soil or rock layer. • California has one of the most extensive distributions of vernal pools in the world. Photo by Carol Witham Some examples of neoendemics Including edaphic endemics The genus Arctostaphylos (Manzanita) Ericaceae (heath family) • 94 taxa in California, most endemic. Photo by Walter Knight Photo by Charles Webber Arctostaphylos myrtifolia, Ione manzanita. Endemic to the Ione soil formation in the Sierra Nevada foothills east of Sacramento. Federally listed as threatened. In addition to habitat destruction, more recent threats to preserved habitat Come from a root and crown rot caused by Phytophora cinnamomi. Arctostaphylos canescens ssp. sonomensis, Sonoma canescent manzanita. Endemic to the North Coast Ranges. Considered rare, threatened, or endangered in California by the California Native Plant Society. Photos by Dean Wm. Taylor Arctostaphylos uva‐ursi, bear‐berry, kinnikinnick. Circumpolar distribution. Occurs in many habitats in CA, from coastal dunes to subalpine forest. Photo by Charles Webber. The genus Ceanothus (California‐Lilac) Rhamnaceae (buckthorn family) • 60 taxa in California, most endemic. Photo by Br. Alfred Brousseau Ceanothus cuneatus, buck‐brush. A common component of chaparral in The Coast Ranges and Sierra Nevada foothills. Ceanothus roderickii, Pine Hill ceanothus. Endemic to the gabbro soils of Pine Hill and vicinity in the Sierra Nevada foothills east of Sacramento. Federally listed as endangered. Photo by Dean Wm. Taylor Ceanothus thyrsiflorus, blue blossom. Native along the coast of California from the north to Baja California. Endemic to the CFP. Photo by Br. Alfred Brousseau The genus Clarkia (farewell‐to‐spring) Onagraceae (evening‐primrose family) • 59 taxa, all annual, most endemic to California. Clarkia concinna ssp. concinna, red ribbons. Endemic to the hills around the Bay Area and the northern Sierra Nevada. Other subspecies are considered rare by CNPS. Photo by Joseph Doughtery Clarkia fransciscana, Presidio Clarkia. Endemic to serpentine soils. Known only from 2 occurrences at the Presidio in San Francisco and 3 occurrences in the Oakland Hills. Federally listed as endangered. Photo by Jo‐Ann Ordano The genus Streptanthus (jewelflower) Brassicaceae (mustard family) • 35 or more taxa, most endemic to California. Streptanthus morrisonii ssp. elatus, Three Peaks jewelflower. Endemic to serpentine soils in the North Coast Ranges. Considered rare, threatened, or endangered by CNPS. Photo by Dean Wm. Taylor Streptanthus polygaloides, milkwort jewelflower. Endemic to mostly serpentine soils in the Sierra Nevada. A hyperaccumulator of nickel. Photo by Aaron Arthur The genus Allium (onion, garlic) Alliaceae (onion or garlic family) • 51 taxa, most endemic to California. Allium peninsulare var. peninsulare, peninsular onion. Native to the Sierra Nevada and Coast Ranges south to Baja California. Endemic to the CFP. Photo by Steven Thorsted. Allium tuolumense, Rawhide Hill onion. Endemic to serpentine soils in the foothills of the Sierra Nevada in Tuolumne County. Considered to be rare, threatened, or endangered by CNPS. Photo by Dean Wm. Taylor California grasslands Most of California’s grasslands now dominated by naturalized annual grasses of Eurasian origin. Harold Heady called these species “new natives.” Avena barbata, slender wild oat Bromus hordeaceus, soft chess Land Management Total 100 million acres Federal 48% (colors below correspond to map) FS 20% BLM 15% NPS 8% Military 4% Other Federal 1% State 7% Lands Commission 4% Other State 2% Parks 1%