What Makes California California: Biodiversity

There are a lot of reasons to love California, particularly as a naturalist.

The world's six major biomes, represented in California:
Top row: Forest (Redwood State Park); Freshwater (Sword Lake); Desert (Joshua Tree National Park)
Bottom row: Marine (Monterey Bay); Grassland (Stanislaus County prairie); Alpine tundra (Yosemite high country)

California is a land of extremes, from submarine canyons to alpine peaks, from high heat and aridity to remarkable snow pack.  It boasts the tallest trees, the most massive trees, and the oldest [non-clonal] trees.  Within its borders, one can stand on the tallest point in the conterminous United States (Mount Whitney, 14,500 feet above sea level) as well as the lowest (Badwater Basin, 282 feet below sea level).

In addition to the greatest difference in elevation, California also has the greatest range of latitude, the highest soil diversity, the largest range of average annual rainfall and the greatest range of average annual temperature in the continental U.S.  While northwestern California may receive over eight feet of rain in a given year, Death Valley may experience less than two inches.  At the same time, temperatures may be well below freezing in the High Sierra, and in the balmy 70's in the desert regions.  At times, California records both the highest and lowest daily temperatures in the nation!

California is, without question, a land of extreme beauty as well, from majestic granite cathedrals and fog-shrouded groves of redwoods, to boundless fields of golden wildflowers and glorious desert sunrises.  California also leads the nation with the most national parks: we have nine, plus the only national seashore on the Pacific Coast and 18 additional units under the National Park Service umbrella, which protect not only natural beauty and biodiversity, but sites of cultural and historic significance as well.

But it is the biodiversity of the state that really makes California astounding.

With all of the world's six major biomes represented - marine, freshwater, forest, grassland, desert and tundra - there is great opportunity for species to adapt to vastly different habitats and specific niches, and thrive within a relatively small area.  Not only is California high in species richness, or sheer number of species represented, but it is also high in endemism.  Endemic species, those found only within a limited range and nowhere else on Earth, abound in California, where they have adapted to a wide variety of very specific habitats.

Map of the California Floristic Province.
Image source: bioone.org

The California Floristic Province, which spills over the borders of California into the very southern tip of Oregon and the northern edge of Baja California (since plants don't recognize political boundaries), is considered one of only three dozen biodiversity hotspots worldwide.  The region includes the northwest coastal forests and Cascade Range, the Sierra Nevada, central west and southwest coasts, the Great Valley, and small portions of southwestern Oregon and northwestern Baja that share similar floras.  Excluded are desert regions with wider distributions outside the state.

To be classified as a biodiversity hotspot, a region must have at least 1,500 species of endemic vascular plants, irreplaceable species found nowhere else.  The region must also be considered threatened, having lost 70% or more of its original vegetation to anthropogenic activities.  Worldwide, biodiversity hotspots account for less than 2.5% of earth's terrestrial surface area, but they are home to almost half of the world's plant and animal species, which are endemic to these hotspot regions.

Collectively, around 2 billion people make their homes in biodiversity hotspots, including some of the world's most impoverished people, who rely on diverse, functioning ecosystems for their livelihoods, as well as for clean water, pollination of vital food crops, and climate regulation.

Map showing the locations of the world's 30+ biodiversity hotspots.
Image source: berkeley.edu

About one third of all species of plants and animals found in the United States are found in California.  Additionally, about one third of all of California's species are considered threatened, and more threatened species are found in California than in any other state.  Habitat loss and invasive species are the two biggest factors contributing to species loss.  Nearly half of California's land area is protected, and a number of conservation actions have been implemented to prevent further loss.

California has the highest plant species richness in the United States, which is another way of saying it is home to more different types of plants than any other state!  Out of California's over 5,000 plant species, nearly one third (about 1,300 species) are endemic, found nowhere else in the world.  A few well-known examples of endemic plants include valley oak (Quercus lobata) and giant sequoia (Sequoiadendron giganteum), but there are many endemic wildflowers and smaller plants as well.  The highest rates of endemism occur in the Coast Ranges, which is also where California's booming human population is concentrated; a disproportionately high number of endemics are found in the highly urbanized San Francisco Bay Area.  Around 200 species of plants are considered by the state to be rare, threatened, or endangered, and about 2,000 more are at risk and considered species of conservation concern.

More than 1,000 distinct vegetation associations have been recognized in California, which is over half of all plant associations found in the entire western United States.  While oak woodland is an example of a plant community, examples of specific alliances or associations within that community include coast live oak woodland and forest, mixed oak woodland and forest, scrub oak chaparral, blue oak woodland and forest, etc.  (Thanks to the California Native Plant Society, a list of all California's vegetation alliances can be found in A Manual of California Vegetation Online.)

A very small selection of endemic California wildflowers.
Top row: Menzie's wallflower (Erysimum menziesii); butterfly mariposa lily (Calochortus venustus); Lindley's blazingstar (Mentzelia lindleyi)
Bottom row: elegant clarkia (Clarkia unguiculata); Monterey Indian paintbrush (Castilleja latifolia); coast rockcress (Arabis blepharophylla)

While much overlooked and oft-maligned, invertebrates account for over 95% of all described animal species on the planet.  Of the world's estimated 1.25 million invertebrate species, which include everything spineless, from worms and octopuses to jelly fish and corals, about 90% are insects.  Perhaps it is not surprising that in California, invertebrate diversity is high; the state leads the nation in invertebrate species richness with an estimated 34,000 species, which is about one third of all invertebrates found in the U.S.  1,600 species of native bees are found in California, which amount to half of all bee species in the United States and Canada.  Just over thirty species of endangered invertebrates are found in California, which is over half of the country's total.  Some noteworthy endangered invertebrates include abalone (Haliotis spp.), fairy shrimp (Branchinecta spp.), and around fifteen species of butterflies.

In our household, starting a conversation with, "Name your top ten favorite California invertebrates" is not uncommon. 
Here are some of mine.
Top row: male Valley carpenter bee; sea anemone; Western tiger swallowtail
Bottom row: hermit crab; green darner; tarantula

67 freshwater fish are native to California's waters, many of which have suffered dramatically due to habitat loss and degradation.  Nearly half of our native fish species are at risk, and freshwater ecosystems have seen greater densities of species extinction than terrestrial systems.  27 species of California's freshwater fish are anadromous, living their adult lives in the ocean and returning to freshwater to spawn, thus linking marine and terrestrial ecosystems.  Salmon are the quintessential anadromous fish, and both Chinook and Coho salmon (Oncorynchus tshawytscha and O. kisutch) are considered threatened in California.

California is home to 51 species of amphibians, which include native frogs, toads and salamanders, and 84 native reptiles, including lizards, snakes, and turtles.  The highest diversity of amphibians is found in the cool, wet parts of the state where rainfall is high, such as mountainous regions and the northwest coastal forests.  Conversely, reptile diversity is highest in hot, dry parts of the state, like the state's desert regions.  Though other states have greater herpetological species richness (more types of reptiles and amphibians), California ranks number one in the nation in terms of the highest number of endemic reptiles and amphibians.  About a quarter of California's 171 species of herptiles are found nowhere else in the world, and about 35 species are listed as threatened or endangered.  Some notable endemics include the Central Valley's own giant garter snake (Thamnophis gigas), the blunt-nosed leopard lizard (Gambelia sila), the California tiger salamander (Ambystoma californiense) and the Yosemite toad (Anaxyrus canorus), all of which are also threatened or endangered.  (Find a complete list of endemic amphibians and reptiles here, and threatened or endangered species here.)

A few herptiles of California.
Top row: desert horned lizard; mountain garter snake; Pacific tree frog
Middle row: long-nosed leopard lizard; desert tortoise; Western fence lizard
Bottom row: Pacific giant salamander; zebra-tailed lizard; chuckwalla

With over 600 observed species of birds (eBird lists 700 as an all-time record) California is considered to have the most species-rich avifauna - the most number of bird species recorded as well as the most number of breeding species - in the United States (followed closely by Texas, Arizona and Florida).  Around 450 species of birds are regularly seen in the state, and more than 300 species breed in California's rich mosaic of habitats.  California contains 177 of Audubon's Important Bird Areas, which is also more than any other state.  Although California only has two truly endemic bird species (the Yellow-billed Magpie [Pica nuttalli] and the Island Scrub-jay [Aphelocoma insularis]), it still has more endemic birds than any other state except Hawaii!  The California Condor (Gymnogyps californianus) is technically an endemic, though in an effort to bring the species back from the brink of extinction, it has been introduced to ranges outside the state, like parts of Grand Canyon National Park.

The California Floristic Province, described above, is home to around ten more endemic and nearly endemic birds, including the California Thrasher (Toxostoma redivivum), California Towhee (Melozone crissalis), Wrentit (Chamaea fasciata), Nuttall's Woodpecker (Dryobates nuttallii), Oak Titmouse (Baeolophus inornatus), and Tricolored Blackbird (Agelaius tricolor); Allen's Hummingbird (Selasphorus sasin), Lawrence's Goldfinch (Spinus lawrencei) and Ashy Storm-Petrel (Hydrobates homochroa) are considered "breeding endemics," which breed almost entirely in the state but migrate or disperse widely outside of California.

Endemic and nearly endemic California birds.
Top row: Lawrence's Goldfinch; Oak Titmouse; Tricolored Blackbird
Middle row: California Thrasher; Yellow-billed Magpie, our TRUE endemic; California Towhee
Bottom row: Nuttall's Woodpecker; Allen's Hummingbird; not our endemic Island Scrub-jay, but the similar California Scrub-jay, a placeholder until I see our island endemic!

Over 200 species of mammals call California and its offshore waters home: 38 species are marine, including whales and dolphins, and 163 are terrestrial.  An additional 26 species of terrestrial mammals have been introduced to California, including troublesome species like nutria (Myocastor coypus), feral pigs (Sus scrofa) and red foxes (Vulpes vulpes), which differ from our native Sierra Nevada red fox (Vulpes vulpes necator) and are a story for another day.  California's mammals represent seven of North America's ten native mammalian orders: the even toed ungulates (Artiodactyla), carnivores (Carnivora), whales and dolphins (Cetacea), bats (Chiroptera), shrews and moles (Insectivora), rabbits and hares (Lagomorpha), and rodents (Rodentia).  An eighth order, Didelphimorphia, to which opossums belong, has been introduced.  The two single-species North American orders California lacks are the manatees (Sirenia) and the armadillos (Xenarthra).  The highest amount of species diversity is found in the small mammal taxa: around half of California's land mammals are rodents (woodrats, kangaroo rats, pocket mice, chipmunks and the like).

Not only does California lead the nation in number of mammal species, it also ranks first in number of both endemic mammals and threatened mammals.  The 17 endemic mammals include the Island gray fox (Urocyon littoralis), the California red tree vole (Arborimus pomo), the salt-marsh harvest mouse (Reithrodontomys raviventris), six species of kangaroo rats (Dipodomys spp.), two species of pocket mice (Perognathus spp.), the San Joaquin antelope squirrel (Ammospermophilus nelsoni), the Mohave ground squirrel (Spermophilus mohavensis), three species of chipmunk (Tamias spp.), and the Mount Lyell shrew (Sorex lyelli).  While these rodents may not be glamorous animals, they are vital to the health of California's ecosystems, acting as seed dispersers and forming a significant amount of protein-rich biomass near the bottom of a complex food web (a nice way of saying rodents are on just about everyone's menu!)  Perhaps unsurprisingly, most of the state's rare and threatened species are found in the southern portion of the state and the San Francisco Bay area, coastal regions with high species richness and endemism, as well as high human populations and detrimental amounts of habitat fragmentation.

Mammals of California
Top row: Belding's ground squirrel; Southern sea otter; coyote
Bottom row: tule elk; American badger; golden-mantled ground squirrel

As I hope you have come to realize, California truly is a remarkable place: a fascinating slice of complex topography and diverse habitat that is perfectly situated along the western edge of the North American continent to lead the nation in biodiversity.  There is no other place quite like it on this great Earth.

Though our state has been plagued by careless human actions over the last two or three hundred years (overhunting, overfishing and overharvesting; urban, suburban and agricultural development; resource mismanagement, land reclamation and water diversion; pollution of soil, water and air; and the introduction of something like 1,500 non-native and potentially invasive species), surprisingly few species have been lost forever to global extinction.  Some have been extirpated from the state, like wolves, grizzly bears, and jaguars, and some have come perilously close to extinction, like the California Condor, but only about 32 species have been lost entirely in the last 200 years.  Despite our history of wanton disregard for the value of intact ecosystems, a new era began around 50 years ago with the birth of the environmental movement and a push toward conservation.  California, it could be said, now also leads the nation in terms of ecological and conservation-mindedness.

A few years ago, a story titled "Back From the Brink" was published by the Endangered Species Coalition spotlighting the ten greatest North American conservation success stories that took place in the forty years following the implementation of the Endangered Species Act in 1973.  Of those ten conservation success stories, seven took place at least partly in California: the Southern Sea Otter, the Humpback Whale, the Peregrine Falcon, the Bald Eagle, the Brown Pelican, the Green Sea Turtle and the diminutive El Segundo Blue Butterfly of Los Angeles and Santa Barbara counties.  While some of these species, plus many others, remain threatened or endangered, things are looking up: greater awareness, both in the scientific community and among the general public, coupled with improved land use practices and the potential for new, innovative ways to coexist alongside wildlife are paving the way toward a brighter future where the value of intact natural ecosystems is more widely appreciated.


Sources:
California Department of Fish and Wildlife
California Native Plant Society
Conservation International
Ecosystems of California
National Audubon Society