Southern California Plant Communities
begin with, the area of Southern California is generally considered to be
from Santa Barbara County on the north, stretching eastward and northward
across the Santa Ynez Mountain Range to Mt. Pinos in Ventura County, and
continuing in a northwesterly direction to include the east slopes of the
White and Inyo Mountains, across the Panamint Range and into Death Valley,
southward to Los Angeles and San Bernardino Counties including the San Gabriel
and San Bernadino Mountains, the Mojave Desert, the New York and Providence
Mountains, and southward still to include Orange, Riverside, San Diego and
Imperial Counties, with areas of Colorado Desert, the San Jacinto Mountains,
Santa Rosa and Santa Ana Mountains, Joshua Tree National Park, and the Salton
Sea region, being bounded by the Mexican border to the south, the Pacific
Ocean to the west, and the Colorado River and Nevada state line to the east.
Thus there are three distinct floristic areas to be considered, the cismontane
area between coast and mountains, the montane areas, and the transmontane
area on the inland or desert side of the mountains. The Channel Islands
off the coast may be considered a fourth floristic area. Technically speaking,
California is divided into two Floristic Provinces, the California Floristic
Province and the Desert Floristic Province. The Great Basin Floristic Province
extends a narrow wedge-shaped area in a southward direction between the
eastern side of the Sierras and the Death Valley region, which at one time
reached its southern terminus in the San Bernadino Mountains.
Rainfall in Southern California can vary from 0-2" annually in Death Valley to around 50" in the higher, wetter reaches of the mountains. The ocean moderates the temperatures of the coastal regions and also adds to their moisture load with fog. Frost is rare near the coast, while above 5000' snow falls in the winter and there are many days of morning frost. Coastal regions are more even in temperature, while inland temperatures, both higher and lower, are more extreme. Southern California is characterized generally by a fairly long dry season with temperatures that can exceed 100 degrees on many days, and relatively short mild winters during which almost all the annual precipitation falls. Another important consideration with regard to rainfall is the recurring cycle of El Nino years which have been occurring on an irregular basis roughly every seven or so years. El Nino years bring increased rainfall to Southern California, and depending upon how they develop may distribute rainfall throughout the fall, winter, and spring seasons. It is during these years that the desert in particular comes to spectacular life. The winter of 1997-1998 was the last El Nino season that we have had in Southern California with roughly three times normal rainfall and ephemeral plants springing up in the desert that hadn't been seen in many years. A further complication in the rainfall pattern is what is being referred to as the Pacific Decadal Oscillation, which is a 10-20 year cycle of dry years and wet years that is not yet well understood, such that if an El Nino occurs during the dry phase, its effects will be significantly mitigated. It appears that Southern California is in the midst of such a dry phase at the moment.
It is important to recognize that plant communities are not always clearly defined entities with strictly delineated boundaries, and that a given species may well inhabit two or more different such communities. Plant communities or associations are typically dependent on or affected by such factors as geographical location, soil types, precipitation rates, angle and direction of slopes, elevations, microclimates and successional considerations, and thus it is not uncommon to find a particular plant or grouping of plants growing outside what would be thought of as its customary habitat if some of the above factors are advantageous to that growth. Depending upon what sources you refer to, there can be literally dozens of plant communities in Southern California, but the major and most widely recognized ones are as follows: (1) coastal salt marsh, (2) freshwater marsh, (3) coastal strand, (4) coastal sage scrub, (5) chaparral, (6) southern oak woodland, (7) valley grassland, (8) riparian woodland, (9) yellow pine or montane coniferous forest, (10) pinyon-juniper woodland, (11) sagebrush scrub, (12) shadscale scrub, (13) creosote bush scrub, (14) desert riparian woodland, (15) joshua tree woodland and (16) alkali sink. I will attempt to give a brief description of each with some of its associated plants.
1. Coastal salt marshes typically include low areas, estuaries and wetlands in immediate proximity to the coast and in the tidal zone of the ocean, often protected lagoons such as Mugu and Malibu, and places which are characterized by at least seasonal inundation by salt water and a high salt content in the soil. Plants in these localities must be adapted to being in salt water at least part of the time and are referred to as halophytes. This necessity produces a distinct succulence and/or compactness compared to similar plants further inland which results in a reduced evaporating surface. Typical plants of coastal salt marsh would include such genera as Salicornia (pickleweed), Suaeda (seepweed) and Limonium (sea lavender), Batis maritima (saltwort), Cuscuta salina (saltmarsh dodder), Jaumea carnosa (jaumea), Spartina foliosa (California cordgrass), Frankenia salina (alkali heath), and several species of Atriplex.
2. Freshwater marshes are the end result of water draining from the mountains, including standing or slowly moving water, mostly below 500', and are wet or semi-dry areas, but with a usually wet substratum. Plants that characterize such habitats include Rorippa nasturtium-aquatica (water-cress), the water smartweeds Polygonum amphibium and punctatum, Polygonum arenastrum (knotweed), Nuphar luteum (pond lily), Typha latifolia (common cattail), Anemopsis californica (yerba mansa), Euthamia occidentalis (western goldenrod), Artemisia biennis (biennial sagewort), Azolla filicoides (mosquito fern), Cyperus eragrostis (tall flatsedge), and species of Lemna (duckweed), Scirpus (tule), Carex (sedge), Juncus (rush) and Potamogeton (pondweed). Examples of freshwater marsh areas may be found at Century Lake, Nicholas Flat Pond, Rocky Oaks Pond, and La Jolla Pond, all in the Santa Monica Mountains. Between salt and freshwater marshes, there may be brackish areas where plants must be adapted to both salty and fresh water.
3. Coastal strand refers to the vegetation of a thin strip of land along the coast, including beaches, dunes and the area between ocean and bluffs. Plants here are customarily succulent, herbaceous, evergreen, perennial and xerophytic. Salt spray and wind have a drying effect, and of course plants on the beaches and dunes above the beaches are periodically affected by significant and powerful storm surges. Species diversity is low and vegetation is spare. A drive along the Pacific Coast highway from Santa Monica to Point Mugu passes through this plant community. Typical plants include Abronia maritima (red sand verbena), Cakile maritima (sea rocket), Ambrosia chamissonis (silver beach-bur), Atriplex leucophylla (beach saltbush), Ericameria ericoides (mock heather), Camissonia cheiranthifolia (beach primrose), Lupinus chamissonis (dune lupine), Distichlis spicata (saltgrass), and the iceplants of genus Carpobrotus and Mesembryanthemum.
4. Coastal sage scrub is often referred to as 'soft chaparral' because its shrubs are not as densely-spaced or as rigid as those of true chaparral, and their leaves are not the thick, tough, sclerophyllus and drought-tolerant leaves that characterize that community. Coastal sage scrub exists mainly below about 3000' and occupies generally drier sites than does chaparral, being developed primarily on western slopes above the beaches, on steep, south-facing wind-exposed slopes, and in areas where the marine layer penetrates further inland to foothills and canyons. This community receives on average about 10"-20" of annual rainfall and is subject only rarely to frost conditions. Shrubs here are not the completely woody shrubs of chaparral and are adapted to long, dry summers in a number of ways. Remaining dormant through the dry season, they either drop leaves or produce smaller leaves on secondary shoots during the summer, which can result in a reduction of water loss by as much as 80%, a characteristic known as seasonal dimorphism. Root systems are generally shallow because the plant is inactive so much of the time. Some shrubs may store water in succulent leaves and stems, and others produce aromatic oils from the leaf surfaces which makes them less appealing to grazing animals and may reduce water loss, but which also increases their flammability during the frequent fires. Coastal sage scrub shrubs are typically fire adapted by seed germination so that there are usually individuals of all ages present. Typical species in this community are Artemisia californica (California sagebrush), Eriogonum cinereum (ashyleaf buckwheat), E. elongatum (long-stemmed buckwheat), E. fasciculatum (California or wild buckwheat), Salvia apiana (white sage), S. mellifera (black sage), S. leucophylla (purple sage), Mimulus longiflorus (bush monkeyflower), Encelia californica (bush sunflower), Baccharis pilularis (coyote brush), Hazardia squarrosus and Isocoma menziesii (sawtooth and coast goldenbush), Malosma laurina (laurel sumac), Trichostema lanatum (woolly blue curls), Venegasia carpesioides (canyon sunflower), Lotus scoparius (deerweed), Eriophyllum confertiflorum (golden yarrow), Opuntia littoralis (coast prickly pear), Lupinus spp. (lupines) and Elymus canadensis (Canadian wildrye).
5. Chaparral is
a plant community which derives its name from the Spanish word
6. Southern oak woodland consists of woody vegetation generally over 15' tall and typically occupies north-facing slopes, shaded canyon ravines and sheltered interior valleys below about 5000', and grades into both valley grassland and riparian woodland. There are sometimes intermittant streams that cross areas of oak woodland, and the annual rainfall is usually between 15" and 25". The dominant trees are the oaks, Quercus lobata, Quercus agrifolia and Quercus engelmannii (valley oak, coast live oak and engelmann oak), Juglans californica (black walnut), Platanus racemosa (western sycamore), Umbellularia californica (California bay laurel), Heteromeles arbutifolia (toyon), and Sambucus mexicana (mexican elderberry), accompanied by Rhamnus californica (coffeeberry), Rhus ovata (sugarbush), Rhus integrifolia (lemonadeberry), Rhus trilobata (squawbush), Toxicodendron diversilobum (poison oak), Dryopteris arguta (coastal wood fern), and Pteridium aquilinium (bracken fern). These smaller trees and shrubs along with herbaceous plants and grasses form a vegetative understory which is an important part of this community.
7. Valley grassland is a community that is regrettably scarce in Southern California and growing scarcer because of agriculture and development. Much of the Central Valley of California remains in some form of grassland, but in our region there are not many areas of more than a few acres. A primary one occupies the La Jolla Valley at the western end of the Santa Monica Mountains and is some 600 acres in extent, and another is the Santa Rosa Plateau adjacent to the Santa Ana Mountains. Beyond the scarcity of grasslands in general, there is the further consideration that such grasslands as do exist have changed greatly in character, passing from native, perennial grasses to introduced, annual species. In Southern California, valley grassland occupies deep, sometimes rocky but usually well-drained soils in hot, interior valleys generally below 4000', often on south-facing slopes but more typically on flatter land, adjacent to and often mixed in with chaparral, coastal sage scrub and southern oak or riparian woodland. Annual rainfall is customarily between 6" and 20", summers are hot and dry and frost is not uncommon in the winter. Although sometimes dotted with oak species such as Quercus lobata (valley oak) and Q. integrifolia (coast live oak), grasslands unsurprisingly are characterized primarily by shrinking expanses of native genera of grasses such as Stipa (needle-grass), Poa (bunchgrass) or Aristida (three-awn), and expanding areas of introduced genera such as Bromus (brome grass), Avena (wild oats) Festuca (fescue), Lolium (ryegrass) and Phalaris (harding grass). Springtime also can bring masses of wildflowers, many native, some introduced, such as Ranunculus (buttercup), Delphinium (larkspur), Calochortus (mariposa lily), Hemizonia (tarweed), Sisyrinchium (blue-eyed grass), Dichelostemma (blue dicks), Castilleja (both paintbrush and owl's clover), Nemophila (both baby blue eyes and meadow nemophila), Lupinus (lupines), Sonchus (sow-thistle), Centaurea (star-thistle) and Erodium (filaree).
8. Riparian woodland is a fairly restricted community because it is dependent on the presence of or proximity to non-seasonal water courses, but nevertheless since water is not abundant in Southern California, this community can be a striking one. Surface water is not always a requirement and may be substituted for by underground water in some places. Where non-seasonal streams flow out of the mountains and onto flatter grasslands, the riparian woodland community may be a relatively broad one, but in the higher elevations where water flows down a narrow passageway often confined by steep hillsides, this community may be only a few meters in width. Riparian woodland may also occupy areas such as the margins of man-made lakes and reservoirs. Typical species of this community include Platanus racemosa (western sycamore), Populus fremontii and trichocarpa (fremont and black cottonwood), Alnus rhombifolia (white alder), Juglans californica (black walnut), Acer macrophyllum (big-leaf maple), Umbellularia californica (California bay laurel), Salix spp. (willows), Baccharis salicifolia (mule fat), and smaller plants such as Epipactis gigantea (stream orchid), Toxicodendron diversilobum (poison oak), Rubus ursinus (California blackberry), Equisetum spp. (horsetails), Lilium humboldtii (humboldt lily), and Mimulus cardinalis and guttatus (scarlet and creek monkeyflower).
9. Montane coniferous forest is here treated as a combination of yellow pine forest and subalpine forest, the former occupying mountain slopes from between 5000' and 8000', and the latter above that to around 9000'-9500'. Because of the elevation, the average annual precipitation is between 35" and 50", some of which falls in the form of winter snow. This forest community is one that inhabits ridgetops and cismontane slopes primarily, which are considerably moister than the slopes on the desert side of the mountains. Typical species encountered in the lower belt of montane forest in Southern California are Pinus coulteri (coulter pine), P. ponderosa (yellow or ponderosa pine), P. jeffreyi (jeffrey pine), P. lambertiana (sugar pine), Calocedrus decurrens (incense cedar), Abies concolor (white fir), Pseudotsuga macrocarpa (big-cone spruce), Juniperus occidentalis (western juniper), Quercus kelloggii and chrysolepis (black oak and canyon live oak), Cercocarpus ledifolius (curlleaf mountain mahogany), Arctostaphylos spp. (manzanitas), Ceanothus integerrimus and cordulatus (deerbrush and snowbush), Chrysolepis sempervirens (bush chinquapin), Rubus parviflorus (thimbleberry), Ribes nevadense and roezlii (Sierra current and Sierra gooseberry), in addition to many species of Lupinus, Eriogonum, Penstemon and Phacelia. Above the yellow pine belt and growing to 9500' are Pinus contorta (lodgepole pine) and P. flexilis (limber pine), and many species of small subalpine wildflowers. One of longest living plant species in North America, Pinus longaeva (bristlecone pine), cannot be truly considered a Southern California species, but it can be found at elevations of from 10,000' to 11,000' in the White and Inyo Mountains to the east of the Sierra Nevadas, and in the Panamint Mountains near the edge of Death Valley.
10. Pinyon-juniper woodland clothes the desert side of the mountains, generally the eastern slopes of north-south trending ranges and the northern slopes of east-west trending ranges, at elevations from about 5000' to 8000'-9000', extending from the Tehachapi Mountains southward and including the higher mountains of the Mojave Desert. This vegetative community is typically sandwiched between either sagebrush scrub or joshua tree woodland and yellow pine forest. Average annual precipitation is between 12" and 20", and some of that is in the form of snow, so obviously this is a much drier environment. As the name suggests, the dominant trees are Pinus monophylla (single-leaf pinyon pine) and Juniperus californica and osteosperma (California and Utah juniper), along with Quercus turbinella (desert scrub oak), Q. john-tuckeri (Tucker's oak), Q. cornelius-mulleri (Muller's oak), Yucca shidigera and baccata (Mojave and banana yucca), Purshia mexicana and tridentata (cliff rose and bitterbrush), Fallugia paradoxa (apache plume), Cercocarpus ledifolius (curlleaf mountain mahogany), and most of the shrubs that make up sagebrush scrub which will be discussed next.
11. Sagebrush scrub is often adjacent to pinyon-juniper woodland and exists on generally deep, permeable soils on the desert side of the mountains along the western edge of the Mojave Desert from the Sierra Nevadas south to the San Bernardinos, and also the mountains bordering the Colorado Desert in San Diego County, in an elevational belt of about 4000' to 7000'-9000'. Summers are very hot and winters can be quite cold, so of the 8"-15" of annual precipitation, a good proportion falls as snow. Generally speaking, this community can be characterized as one of fairly low, silvery-gray shrubs of less than 6' in height, and it takes its name from three species of sagebrush that inhabit it: Artemisia cana (silver sagebrush), A. nova (black sagebrush), and A. tridentata (great basin sagebrush). Other species common in this community are Chrysothamnus nauseosus and viscidiflorus (rubber and yellow rabbitbrush), Coleogyne ramosissima (blackbrush), Atriplex canescens and confertifolia (fourwing and shadscale saltbush), Tetradymia spp. (horsebrush) and Purshia tridentata (bitterbrush or antelope bush).
12. Shadscale scrub is another desert scrub community, and whereas herbaceous and woodland communities in California are best developed in the northern part of the state, so-called scrub communities are best developed in Southern California. Scrub is a term that refers to the fact that most of the plants in the community are fairly low (< 6') shrubs. This community occupies areas near or adjacent to joshua tree woodland, but on quite different types of soils. Shadscale scrub typically grows on very heavy, often alkaline or saline soils which are underlain by an impermeable hardpan strata, and is found on mesas and flatlands from about 3000' to 6000' in various parts of transmontane desert regions such as the Owens Valley and the Mojave Desert, where the summers are very hot and dry and the annual rainfall averages only 6"-10". It is rare in the Colorado Desert where its niche is usually taken up by creosote bush scrub. The shrubs in this community are generally small, with small leaves and small flowers, grayish, intricately-branched and often spiny. This community takes its name from its dominant shrub, Atriplex confertifolia (shadscale), and includes such other species as Grayia spinosa (hopsage), Kraschenennikovia lanata (winter fat), Artemisia spinescens (spiny sagebrush or budsage), Gutierrezia spp. (matchweeds), Hymenoclea salsola (cheeseweed), Coleogyne ramosissima (blackbrush), Menodora spinescens (spiny desert olive or greenfire), and various species of Ephedra (mormon tea).
13. Creosote bush scrub is one of the most widely distributed desert communities, and anyone who drives through any areas of either the Mojave or Colorado Deserts is bound to pass through seemingly endless miles of almost symmetrically-spaced creosote bushes. The majority of the desert floor and the lower slopes of foothills to about 3500' is covered by this scrub community, the soils being well-drained, and the climate consisting of very high summer temperatures and winter temperatures rarely approaching freezing, with annual average rainfall being about 0"-2" in a dry year to about 8" in a wet one. One of the things that distinguishes both this community and joshua tree woodland is the fact that some of the annual rainfall arrives in the form of summer showers, so that there are many shrubs and annual species that bloom either in the summer or in the fall. And although creosote bush scrub is dominated by woody shrubs, both herbaceous annuals and perennials are well represented, and in a rainy season such as we had in 1997-1998, the normally barren ground is literally covered with bloom. As the name indicates, this community is dominated by Larrea tridentata (creosote bush), but also heavily populated by Ambrosia dumosa (burroweed), Fouquieria splendens (ocotillo), Psorothamnus arborescens and schottii (Mojave and Schott's indigo bush), Lycium brevipes and andersonii (desert thorn and Anderson's desert thorn), Hymenoclea salsola (cheesebush), Encelia farinosa and frutescens (brittlebush and rayless encelia), Sphaeralcea ambigua (apricot or desert mallow), and Opuntia basilaris, bigelovii and echinocarpa (beavertail, teddybear and silver or golden cholla).
14. Desert riparian woodland is a community that exists along permanent or seasonal watercourses through several other communities in both deserts, and is not always considered as a separate community, but I feel that enough of the plants that grow there are more or less confined to that area to justify it as such. During a dry year, very little water may pass along these washes, but in a wet year they are inundated, and it is during those periods that the plants can germinate and disperse. Many of the species that grow there produce seeds that require scarification, that is, the grinding action of water and stony soil, to break open their outer casings and begin the germination process. Often such plants appear to go into a dormant state after germination and the production of a few leaves, but what is actually happening is that the plant is using its energy to send down deep roots to be able to take advantage later of sources of water when surface water has disappeared. Typical plants that inhabit this community are Prosopsis glandulosa (honey mesquite), Psorothamnus spinosus (smoke tree), Cercidium floridum (blue palo verde), Olneya tesota (ironwood), Pluchea sericea (arrowweed), Chilopsis linearis (desert-willow), Acacia greggii (catclaw acacia), Justicia californica (chuparosa), and Hyptis emoryi (desert lavender). Some of these species can be found in areas other than riparian ones, but along desert washes this is a fairly distinct community.
15. Joshua tree woodland is another community that is marked by a total domination by a single species. The joshua tree, Yucca brevifolia, is actually a member of the lily family, and it is joined by another lily, Yucca shidigera (mojave yucca), in covering an area that extends right across the Mojave Desert from the Owens Valley to the Little San Bernadino Mountains at elevations of about 2500' to 6000' on generally well-drained slopes and flatlands. In addition to the two lilies mentioned above, neither of which would be recognized by the average person as a lily, other typical species that grow here are Juniperus californica (California juniper), Salazaria mexicana (paperbag bush), Lycium andersonii and cooperi (Anderson's desert thorn and boxthorn), Salvia spp. (sages), Eriogonum fasciculatum and inflatum (wild buckwheat and desert trumpet), Ephedra spp. (mormon tea), Opuntia spp. (chollas), and Tetradymia axillaris, glabrata and stenolepis (cottonthorn, little horsebrush and mojave horsebrush). As was true of creosote bush scrub, joshua tree woodland can produce an extraordinary wildflower display in years when the rainfall has been abundant, and anyone who has travelled through Joshua Tree National Park at such a time is fortunate indeed.
16. Alkali sink is a rather unattractive community dominated by members of the family Chenopodiaceae, a family many of whose members are exceedingly salt tolerant. The environment where this community prospers is one of generally poorly drained alkaline soils and dry Mojave Desert lake beds on the desert floor, especially in the Panamint Valley and Death Valley regions, low places which are only resupplied by water by the occasional heavy winter rainfall and where standing water evaporates rather quickly. Representative plants of this community are Atriplex polycarpa (allscale), A. spinifera (spinescale), A. lentiformis (big saltbush), A. parryi (Parry's saltbush), Suaeda moquinii (bush seepweed), Allenrolfea occidentalis (iodine bush), Salicornia spp. (pickleweeds), and Sarcobatus vermiculatus (greasewood). Just as is true of many plants in the saltwater marsh community, a normal characteristic of alkali sink plants is fleshy leaves and stems, and it is not surprising that a couple of these species occupy both habitats.