The Hills and Mountains ringing Los Angeles(Chaparral and Sage Scrub natural communities) had a far different eco-complex than did the actual San Fernando and Ventura Valley floors which were prairies with riparian(rivers and streams) corridors interlaced throughout..............The Chaparral/Sage mountains saw Pumas, Coyotes and Bobcats at the top of the carnivore food chain with the Prairie valleys featuring Grizzly Bears and Coyotes..........."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"

https://www.sfvaudubon.org/natural-history-of-the-san-fernando-valley/


NATURAL HISTORY OF THE SAN FERNANDO VALLEY

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. 

Chaparral on hillside in Los Angeles

 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).

Coastal Sage/Oak in the Los Angeles foothills

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.

 Puma and Coyote in the Chaparral/oak sage communities

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. 

Rendition of Pronghorns in the San Fernando Valley-prairies ecosystem

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 of 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. 

What Grizzlies would have appeared like on the prairie
floor of the San Fernando Valley

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.

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.”

 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.  

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.

   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.