Paula M. Schiffman, Ph.D.
Department of Biology
California State University
Northridge, CA 91330-8303

Mediterranean-type Climate and the Local Ecological Landscape

Southern California’s climate of hot, dry summers and cool winters with annually varying rainfall is largely responsible for determining the species composition of our wildlands.  This climate, which is known as a Mediterranean-type climate because it is very much like that of the region surrounding the Mediterranean Sea, is produced by the complex interactions of cold ocean currents, latitude, and continental terrain.  This type of climate is found nowhere else in North America.  In fact, other than parts of California and the Mediterranean region itself, only a few other far-flung places on Earth are characterized by Mediterranean-type climates:  central Chile, South and Western Australia, and the Cape region of South Africa.

Our local native plants and animals are adapted to this Mediterranean-type climate.  They have special biological features that enable them to deal with the stresses produced by very bright sunlight, tremendous summertime heat, and many months without rainfall.  The chaparral and coastal sage scrub ecosystems developed on southern California’s hillsides after the Pleistocene ice age ended about 10,000 years ago.  Chaparral vegetation is made up of very densely growing shrubs with sclerophyllous leaves (tough, leathery, evergreen leaves that resist wilting in the summer).  Plants species such as chamise (Adenostoma fasciculatum), California lilac (Ceanothus spp.), and scrub oak (Quercus berberidifolia) dominate this ecosystem.  Like chaparral, coastal sage scrub is a shrubby type of vegetation capable of growing on steep, rocky slopes.  However, the plants do not grow as densely and many of them are drought deciduous (they avoid drought stress by dropping their leaves in the heat of summer and only produce new leaves when winter rains begin).  Buckwheat (Eriogonum fasciculatum), sages (Salvia spp.), and sagebrush (Artemisia californica) are important coastal sage scrub species.  In addition, some slopes and canyons support woodlands of oak (Quercus agrifolia and Q. lobata) and walnut (Juglans californica).  These hillside vegetations provide habitat for a multitude of wildlife species including mammals such as bobcats (Felis rufus), mountain lions (Felis concolor), and coyotes (Canis latrans), and birds including Wrentits (Chamaea fasciata), California Thrashers (Toxostoma redivivum), Western Scrub-Jays (Aphelocoma californica), California Quail (Callipepla californca), and Anna’s Hummingbirds (Calypte anna), to name just a few.  Although our local hillside ecosystems have become increasingly vulnerable to clearing for suburban development, tracts of chaparral, coastal sage scrub, and woodland still remain intact in the Santa Monica Mountains, Santa Susana Mountains, Simi Hills, and Verdugo Hills surrounding the San Fernando Valley.

But what about the San Fernando Valley itself?  Today it is a complex human-dominated environment of suburban houses, backyard gardens, businesses, streets, and freeways.  What was its ecology like before people so massively transformed it, when it was still a wild environment?  Historically, the Valley’s rather flat terrain and often dense, clayey soils were carpeted by a prairie (or grassland) of colorful wildflowers, grasses, and other plants of rather low stature.  In addition, riparian (riverside) corridors of willow (Salix spp.), alder (Alnus rhombifolia), sycamore (Platanus racemosa), and mulefat (Baccharis salicifolia) grew along the Los Angeles River floodplain and the creeks that flow across the Valley and feed into it.  This prairie and riparian vegetation was quite different than chaparral and coastal sage scrub and, therefore, the ecology of the Valley floor was also quite different than that of the surrounding shrubby hillsides.  For example, groups of pronghorn antelope (Antilocapra americana), North America’s fastest running mammal, roamed the Valley floor.  They ate the native wildflowers that carpeted the Valley and, because they were adapted to the open and mostly treeless environments of plains and prairies, they did not venture too far into hillside thickets of chaparral and coastal sage scrub. In 1775, Pedro Font, a Spanish priest described in his diary an observation made in the Conejo Valley (west the San Fernando Valley) of “a very large drove of antelopes which as soon as they saw us, fled like the wind, looking like a cloud skimming across the earth.”  Early records like this one help us visualize what this historical prairie ecosystem was like because it no longer exists today.

In fact, the historical San Fernando Valley prairie was habitat to a great deal of wildlife diversity.  Birds adapted to wide open spaces, such as Western Meadowlarks (Sturnella neglecta) and Horned Larks (Eremophila alpestris), were particularly common. The magnificent California Condor (Gymnogyps californicus; now an endangered species protected by the state and federal governments), was also frequently seen soaring above the Valley.  Small mammals, particularly cottontail rabbits (Sylvilagus audubonii), black-tailed hares (Lepus californicus), California ground squirrels (Spermophilus beecheyi) and valley pocket gophers (Thomomys bottae) were also extremely numerous.  The large numbers of these animals so impressed southern California’s earliest European and American settlers that several people actually wrote vivid descriptions in their journals about seeing thousands of rodents in flatland areas like the San Fernando Valley.  Ground squirrels and pocket gophers were especially notable because their burrowing activities left holes in the soil that made travel by horseback or wagon difficult.  In 1832, an early Los Angeles resident, Hugo Reid noted that ground squirrel diggings “so honeycombed the surface of the ground as to make it dangerous to ride anywhere off the roadway faster than a walk.”  

These small mammals were the food base for a large number of native predators, including coyotes, long-tailed weasels (Mustela frenata), and badgers (Taxidea taxus), as well as many snake and hawk species.   The region’s most high profile predator, however, was the grizzly bear (Ursus arctos).  Grizzlies excavated the soil with their enormous claws in search of rodents, roots, bulbs, fungi, and insect grubs.  Because of the abundance of these foods in the prairie ecosystem, the San Fernando Valley was grizzly bear habitat.  In 1861, concern about the danger of grizzly bears was on the mind of the scientist, William H. Brewer, as he explored the Santa Susana Mountains.   In his journal he described hurrying back to the perceived safety of his group’s campsite at the base of the mountains because “I was alone, far from camp – grizzlies might come out as the moon came up, for the weather was warm.”  Because California’s early European and American settlers felt threatened by grizzly bears, they aggressively hunted down bears and shot them.  A skull of a grizzly killed in 1875 at the San Fernando Mission is now housed as a museum specimen at the Smithsonian Institution in Washington, D.C.  Because of this intense hunting, grizzlies were extinct in California by the early part of the 20th Century.  One of the last surviving individuals was killed in 1916 just north of the San Fernando Valley in Big Tujunga Canyon.  Ironically, the fierce, but locally extinct, grizzly bear still emblazons the California state flag and we proudly recognize it as our official state animal.

Native People and Their Ecological Effects

The first human inhabitants of the Los Angeles area were the Tong-va (also known as Gabrielino) people.  In the San Fernando Valley there is archeological evidence of 10 distinct Tong-va communities.  Each of these communities was located where the prairie of the valley floor interfaced with the surrounding mountain slopes.  Locations where settlements were established had dependable sources of freshwater and wild foods, as well as protection from flooding.  The number of people living in these native communities is difficult to estimate because, within just a few years of their first contact with European explorers and Spanish missionaries, mortality caused by European diseases and brutal treatment devastated the Tong-va population.  It is clear, however, that the pre-contact population would have been considerably larger in size than the 100 inhabitants (or less) per community documented in mission records in 1797.

The people in the San Fernando Valley’s Tong-va communities utilized a diversity of natural resources for food, shelter, and cultural purposes.  The acorns produced by oaks were a staple of their diet.  They also ate many other types of fruits and seeds, including prickly pear cactus (Opuntia littoralis), hollyleaf cherry (Prunus ilicifolia), chia (Salvia columbariae), and red maids (Calandrinia ciliata), and onion-like bulbs such as blue dicks (Dichelostemma capitatum).  They ate grasshoppers and a variety of insect larvae.  Rabbits, rodents, antelope, and mule deer (Odocoileus hemionus) were hunted using bows and arrows constructed from branches and twigs of plants including elderberry (Sambucus mexicana), willows, and wild rose (Rosa californica).  Baskets were woven from skunkbrush (Rhus trilobata), grasses, willows, and rushes (Juncus spp.) and the wood from trees such as oaks, willows, and sycamore were used to construct houses, canoes, mortars, platters and many other basic items used in daily life.

Because the Tong-va depended upon local organisms for survival, they actively managed their environment in the San Fernando Valley to promote and maintain habitats of useful plants and animals.  For example, they purposefully set fires to increase the productivities of important food plants such as chia, red maids, clovers (Trifolium spp.), and blue dicks.  These fires also improved hunting by increasing forage for wildlife.  In addition, it is likely that the Tong-va people promoted the growth of useful plants through small-scale cultivation, broadcasting seed, and coppicing (pruning stems from shrubs or trees to enhance new growth).  These intentional manipulations of the environment enabled the native people to exert considerable control over the region’s vegetation and animal populations.  Nonetheless, compared to the modern-day extent of human dominance in the San Fernando Valley environment, the landscape that the Tong-va inhabited was still very wild.


Ecosystem Changes During the Past 200+ Years

European settlement, which was initiated by the Spanish missionaries in the late 1700s, radically changed southern California.  Flatlands, including the San Fernando Valley, were converted to agricultural uses and livestock grazing became the region’s most widely established agricultural practice.  Enormous herds of cattle fed on the prairie vegetation.  In an 1861 diary entry, William H. Brewer described the San Fernando Valley as having “no fences, the cattle half wild and require many horses to tend them.  A ranch with a thousand head of cattle will have a hundred horses.”  In addition, numerous sheep and hogs were also released to forage in the prairie ecosystem.  These large domesticated animals were very different from the Valley’s native herbivores (antelope, rabbits, rodents, grasshoppers, etc).  Intense livestock grazing was a new mode of disturbance in this habitat and it was extremely disruptive to native species.  Many wild plants were unable to tolerate so much herbivory.  According to cowboy chronicler Dane Coolidge, “in 1805, thirty-five years after the first herd was brought in, they were killing cattle in the San Fernando Valley because they were destroying the grass.”  Not only did overgrazing disrupt the livestock industry, it also severely disrupted the wild ecosystem that provided the food base.  Overgrazing magnified the natural stresses caused by periodic floods and droughts.  The effects cascaded through the entire system negatively affecting native species in unexpected ways.

One of the major ecological changes that resulted was a massive invasion of plants from Europe’s Mediterranean region.  These species included yellow mustards (Brassica nigra and Hirschfeldia incana), filaree (Erodium cicutarium), and many annual grasses including wild oats (Avena spp.) and red brome (Bromus madritensis).  These invasive species were inadvertently transported to California as seed contaminants of ship ballast, crop seed and nursery stock, or by adhering to the fur of imported livestock.  Once here, their seeds were spread by livestock and they rapidly became naturalized.  These invasive alien species were very opportunistic.  They were more tolerant of the effects of livestock grazing than most native plant species and they competed intensively for water, nutrients, and space.  They displaced native plants and came to dominate prairie environments like the San Fernando Valley.  These invaders are still widespread today and can be found in Valley parks and vacant lots, and also in the hills in open spaces between shrubs or trees.  They continue to compete with native species for limited amounts of resources and, therefore, these invaders are considered to be biological pollutants.

Over time, large citrus orchards replaced the herds of livestock in many San Fernando Valley prairie areas.  Later, following World War II, suburban development began to displace the orchards.  These citrus orchards and then housing tracts transformed the Valley’s once largely treeless prairie landscape into a landscape in which non-native trees were increasingly common. This trend has continued and today our gardens, streets, and parks are planted with an enormous array of ornamental trees and shrubs – species that originated all over the world.   Not only is the Valley’s prairie gone, the Los Angeles River and its feeder creeks now flow through stark cement channels and the riparian woodland corridors of alder, willow, mulefat, and sycamore that once dissected the prairie are also gone.  

Yet, despite the tremendous environmental changes associated with increasing urbanization, wildlife still can be found throughout the San Fernando Valley.  In particular, a wide variety of wild birds, including Mockingbirds (Mimus polyglottos), Lesser Goldfinches (Carduelis psaltria), Bushtits (Psaltriparus minimus), Mourning Doves (Zenaiada macroura), Western Scrub-Jays, Great-horned Owls (Bubo virginianus) and hummingbirds can be found inhabiting our garden shrubbery and street trees.  Interestingly, most of these species naturally occur in the woodlands, chaparral, and coastal sage scrub in the hills surrounding the Valley.  They have simply expanded their habitat usage to include the suburban ornamental woodland that replaced the prairie on the Valley floor.  This human-dominated environment also provides habitat for several bothersome, opportunistic, and invasive animal species that are not native to California including black and Norway rats (Rattus rattus and R. norvegicus), fox squirrels (Sciurus niger), Virginia opposums (Didelphis virginiana), Rock Doves (Colulmba livia), European Starling (Sturnus vulgaris), and House Sparrows (Passer domesticus).


Challenge for the Future

The ecology of the Valley has changed considerably since the time when the Tong-va were its human inhabitants and prairie plants supported pronghorn antelope, grizzly bears, and thousands of ground squirrels.  Although the San Fernando Valley prairie no longer exists, many wildlands do still remain in relatively intact condition in the mountains and canyons throughout the Mediterranean-type climate region of California.  Much of this land is owned by federal, state, and municipal government agencies, along with a few private conservation organizations, and environmental protection and ecological restoration are the primary management objectives in these areas.  Still, suburban development continues at a breakneck pace and our remaining wildlands are increasingly threatened by human encroachment.  Recently, California’s Mediterranean-type climate region was ranked by an international group of scientists as being among the Earth’s top twenty-five “biodiversity hotspots” for which stepped up conservation efforts should be a priority.  This hotspot designation highlights the uniqueness and variety of plants and animals in our wonderful natural environment.  It also points to our duty to serve as its vigilant stewards and vocal advocates.  This is a responsibility that we all share as members of the San Fernando Valley ecosystem.

Recommended Additional Reading

Dallman, Peter R. 1998. Plant Life in the World’s Mediterranean Climates.  California Native Plant Society (Sacramento, California) and University of California Press (Berkeley, California).

Gumprecht, Blake. 1999. The Los Angeles River:  Its Life, Death, and Possible Rebirth.  Johns Hopkins University Press (Baltimore, Maryland).

McCawley, William. 1996. The First Angelinos:  The Gabrielino Indians of Los Angeles. Malki Museum Press (Banning, California) and Ballena Press (Novato, California).

Schoenherr, Allan. A. 1992. A Natural History of California. University of California Press (Berkeley, California).


All Rights Reserved