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Lecture: The Coastal Sage Scrub Plant Community
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Coastal Sage Scrub: The native vegetation bordering the Palomar College Arboretum is called coastal sage scrub, a unique plant community or assemblage of dominant plants that are indigenous to this region. This is a low scrubland plant community along the California coastal mountains extending south into northern Baja California. It is divided into two geographical subtypes: Northern and southern coastal sage scrub. It is characterized by low-growing, aromatic, drought-tolerant shrubs adapted to a Mediterranean climate characterized by a winter wet season followed by a prolonged summer drought. It is often referred to as "soft chaparral" because the shrubs are not as tall, woody and densely spaced or as rigid as those of true chaparral, and their leaves are not as thick, tough and leathery (sclerophyllous). Coastal sage scrub receives an average of 10 to 20 inches of annual rainfall, and is subject only rarely to frost conditions. The presence of scattered shrubs of laurel sumac (Malosma laurina) above the Arboretum indicate a relatively frost free climate. In fact, Avocado growers in southern California have used laurel sumac as an indicator of frost free areas. Coastal sage scrub generally occurs below 2,000 feet, primarily on dry, west-facing or south-facing slopes. For example, the south and west-facing slopes of Owens Peak ("P" Mountain) north of Palomar College are covered by coastal sage scrub; however, the northern slopes contain some indicator shrubs of true chaparral. Native soil in the Arboretum hillside is decomposed granite (DG) derived from the gray monzogranite bedrock. Nearby Owens Peak ("P" Mountain) is composed of Santiago Peak metavolcanic rock, a dark, fine-grained, very hard rock that dates back to the Jurassic Period, 145 million years ago, when dinosaurs walked the earth. This heavy rock is resistant to erosion and forms some of the higher topography in coastal San Diego County, including Owens Peak and nearby Double Peak in San Marcos.

Behr's Metalmark
Most of the dominant shrubs in coastal sage scrub are classified as "semi-woody," compared with scattered woody shrubs of toyon (Heteromeles arbutifolia), lemonade berry (Rhus integrifolia) and laurel sumac. Dominance refers to the percentage cover, typically measured by line intercepts (transects) placed randomly over the hillsides. By far, the dominant shrubs are California sagebrush (Artemisia californica), black sage (Salvia mellifera), bush sunflower (Encelia californica), red bush monkeyflower (Mimulus aurantiacus var. puniceus) and golden yarrow (Eriophyllum confertiflorum). Another dominant shrub called wild buckwheat (Eriogonum fasciculatum), is the primary food source for the caterpillar of Behr's metalmark (Apodemia mormo virgulti). In fact, this butterfly is an indicator of coastal sage scrub.

Shrubs of the coastal sage scrub are adapted to the long, dry summers in several ways. Remaining dormant throughout the dry season, they may lose 80% of their water. During this time they may drop many of their brittle, shriveled leaves or produce smaller leaves on secondary shoots. Root systems are generally shallow because the plants are inactive much of the time. It is relatively easy to clear away desiccated shrubs with a heavy hoe during the summer drought season, compared with well-anchored shrubs of true chaparral. The oily, resinous leaves also help to conserve vital moisture, but increase their flammability. The dominant shrubs are fire adapted with seeds that readily germinate after fire. This also includes numerous species of post burn wildflowers that bloom in profusion following the winter and spring rains. These shrubs are vulnerable to excessive or poorly-timed fires, particularly when competing with naturalized grasses and other weedy species. The common vine throughout the coastal sage scrub called wild cucumber (Marah macrocarpus) sprouts soon after fires from a large, subterranean caudex. Under ideal natural conditions, complete recovery of coastal sage scrub after a fire is about 15 to 20 years.

The native scrub vegetation adjacent to the Palomar College Arboretum is not chaparral. It does not contain all the dominant shrubs of true chaparral, such as chamise (Adenostoma fasciculatum), scrub oaks (Quercus), California lilacs (Ceanothus), mountain mahogany (Cercocarpus) and manzanitas (Arcostaphylos & Xylococcus), although the latter shrubs are common in the nearby San Marcos and Merriam Mountains that border Twin Oaks Valley. Our coastal sage scrub is an endangered plant community in coastal San Diego County, primarily due to the clearing of land for agriculture and housing developments. It has been estimated that less than 20% of the original extent of this vegetation may remain in southern California. Coastal sage scrub contains some seriously threatened birds, reptiles and insects, such as the California gnatcatcher (Polioptila californica). In fact, the latter bird was documented in our local coastal sage scrub during an environmental impact study contracted to Palomar College. This plant communty has been extensively studied by wildlife biologists and numerous articles have been published about it. Governmental agencies such as the U.S. Fish & Wildlife Service and California Department of Fish & Game are well aware of its endangered status. For these reasons, it is very important to refer to our local native vegetation as coastal sage scrub and not chaparral. In a given region, the most dominant species has the greatest percent cover. One method for determining dominance is called the line intercept. This method is useful for analyzing a shrub community such as the chaparral or coastal sage scrub. A 100 foot steel tape measure is placed at random in the area to be sampled. The distance that each species overlies (or underlies) the transect line is recorded in feet to the nearest tenth. Dominance is then calculated from the following relationship: Dominance = total distance covered by a species divided by the total distance of line intercepts.

Above figure from Biology Laboratory Manual & Workbook (Fifth Edition) by W. P. Armstrong (1988).
Dominance refers to the area covered by the crown of a shrub or tree species, and is usually expressed as a percent. The shrub or tree canopy provides food, shelter and numerous niches for animal inhabitants. It supplies a layer of litter or duff to the forest floor in the form of dead branchlets and leaves. The vegetation canopy greatly modifies the understory environment by providing shade that results in cooler temperatures and less evaporation. Dense chaparral and coastal sage scrub vegetation on rugged hillsides of southern California also help to reduce excessive soil erosion due to heavy rains. Dominance may be expressed in absolute or relative values.

Absolute Dominance = total distance covered by a species divided by the total distance of line intercects x 100.

For large trees such as ponderosa pine, dominance is based on the total basal area of trunks rather than the area covered by the crown (canopy). The basal area of each trunk is measured at breast height or 4 1/2 feet from the ground. The total basal area can be determined from the density of a species. Absolute dominance is often expressed in square feet per acre rather than as a percent.

Relative Dominance = dominance value of a species divided by total dominance values of all species in study area x 100.

Other useful quantitative values include density and frequency of occurrence: Absolute Density = total number of individuals of a species divided by total area of sample.

Relative Density = Number of individuals of a species divided by total number of individuals of all species x 100.

Absolute Frequency = Number of samples in which a species occurs divided by the total number of samples x 100.

Relative Frequency = Frequency of a species divided by total frequency values for all species in study area x 100.

After calculating the relative values for dominance, density and frequency, importance values (IV) can be determined for each species in study area in order to rank the species according to their magnitude of importance. Importance value is a very useful quantitative parameter, especially when comparing the composition of vegetation from different study areas. The importance values of all species in a given study area should add up to 300.

Importance Value = Relative Dominance + Relative Density + Relative Frequency.

Coastal sage scrub in dormant, dessicated, very flammable state during early September. The leaves are dried up, shriveled and brittle. In the picture are three dominant shrubs: California sagebrush (Artemisia californica), black sage (Salvia mellifera) and wild buckwheat (Eriogonum fasciculatum).

Left: Woodson Mt. Granodiorite from the Merriam Mts. Right: Bedrock "gray granite" (monzogranite) from construction site of new Palomar College Science Building adjacent to the Arboretum. Steve Spear of Palomar College and Mike Walawender of San Diego State University (retired) recently mapped this bedrock as monzogranite (personal communication, 2007).

Santiago Peak Metavolcanic rock from the summit of Owens Peak, better known as Palomar "P" Mountain. This dark, fine-grained, very hard rock dates back to the Jurassic Period, 145 million years ago, to a time when dinosaurs walked the earth. This heavy rock is resistant to erosion and forms some of the higher topography in coastal San Diego County.

Rock & Lichens On OwensPeak
  San Marcos and Merriam Mountains  

Behr's metalmark (Apodemia mormo virgulti), a small butterfly with a wingspan of 2.5 cm, is an indicator of coastal sage scrub. The caterpillar feeds on wild buckwheat (Eriogonum fasciculatum). These butterflies were hilltopping on Owens Peak north of Palomar College (10 September 2010).

Silver argiope (Argiope argentata) on Owens Peak (28 October 2010).

  See Banded Argiope On Owens Peak  
See A Tarantula on Owens Peak

Division Lycophyta: Selaginellaceae (Club-Moss Family)

Spike-Moss (Selaginella bigelovii) growing in crevice of granite boulder.

This is a primitive vascular plant in the ancient division Lycophyta that included tree-like forms dating back to the Carboniferous era 300 million years ago. It is related to club-mosses of the genus Lycopodium. The evergreen, scale-like leaves resemble a conifer, except these plants are low-growing and mat-like (cespitose). In size and growth form they superficially resembling mosses; however, true mosses are nonvascular plants that belong to the division Bryophyta.

  Major Botanical Divisions  
Images Of Lycophytes

Paeoniaceae: Peony Family

Wild peony (Paeonia californica), showing many stamens and three pistils.

This is an interesting native perennial that appears in the Arboretum each spring after sufficient rainfall. The fruit is composed of three (or five follicles), each developing from a separate carpel (pistil). When describing flowers such as these, the term gynoecium is preferable to the term pistil. The gynoecium is a collective term for the carpels of a flower. Monocarpous flowers are composed of one carpel (a simple pistil). The terms apocarpous and syncarpous refer to compound pistils composed of more than one carpel. Apocarpous flowers contain two or more distinct carpels (such as the peony shown above). In syncarpous flowers, two or more carpels are fused together.

See The Apocarpous Gynoecium Of Larkspur
  See The Syncarpous Gynoecium Of Cheeseweed  

Buttercup Family (Ranunculaceae)

Left: A population of scarlet larkspurs (Delphinium cardinale) in the coastal sage scrub adjacent to the Palomar College Arboretum. Right: A magnificent scarlet larkspur in full bloom. The five sepals are bright red, one of which forms an elongate spur.

Southern California clematis or virgin's bower (Clematis pauciflora) climbing down granite boulders in Palomar College Arboretum. There are 3 species native to San Diego County.

Lily Family (Liliaceae)

Weed's Mariposa Lily (Calochortus weedii var. weedii). This beautiful native wildflower grows wild in the coastal sage scrub adjacent to the Palomar College Arboretum.

Snapdragon Family (Scrophulariaceae)

Note: Computer generated monophyletic clades based on chloroplast DNA have resulted in drastic changes to the Scrophulariaceae. Plantago, Penstemon, Veronica, Linaria, Antirrhinum, Keckiella, & Digitalis are now placed in the Plantaginaceae. Mimulus with its thigmotropic stigma is placed in the Phrymaceae. Traditional genera retained in the Scropulariaceae include Verbascum and Scrophularia. Other genera placed in the Scrophulariaceae include Buddleja and Myoporum. Indian paintbrush (Castilleja), Indian warrior (Pedicularis), and owl's clover (Orthocarpus) are placed in the parasitic family Orobanchaceae with the broomrapes (Orobanche). Other closely-related families representing separate clades are the Paulowniaceae, Lentibulariaceae, Acanthaceae and Bignoniaceae.

Red bush monkeyflower (Mimulus puniceus), one of the most colorful shrubs of the coastal sage scrub during late spring. Close-up view at right shows the white stigma in the open and closed positions. The remarkable stigma is "thigmotropic" and can close up rapidly with the slightest touch of your finger or an incoming pollinator, such as the bill of a hummingbird. This action decreases the chance of self pollination and favors cross pollination, especially if the incoming pollinator is covered with pollen from another monkeyflower blossom. When the bill or head of the hummingbird enters the blossom and touches the stigma it immediately closes. Pollen carried by the bird is trapped within the closed stigma lobes. As the bird probes for nectar deep in the corolla it also picks up fresh pollen from the anthers. But when it leaves, there is little chance of this newly acquired pollen touching the stigma because it is already closed, thus averting any self pollination. Note: In the epson Flora of California(1993), this species is listed under M. aurantiacus, in a complex hybridizing, intergrading population that includes a number of subpopulations that were considered separate species in older references. [Incl. M. puniceus, M. longiflorus, M. flemingii and M. aridus.] In the revised Jepson Flora of California it will be listed as Mimulus aurantiacus var. puniceus in the family Phrymaceae.

Red bush monkeyflower (Mimulus aurantiacus var. puniceus). Thigmotropic stigma is in open position.

Waterleaf Family (Hydrophyllaceae)

Yerba santa (Eriodictyon crassifolium) native to the coastal sage scrub east of Palomar College. Unlike the sticky, resinous yerba santas, this species has gray, feltlike foliage covered with a layer of dense, matted, woolly hairs.

Pale lavender flowers and gray, feltlike leaves of yerba santa (Eriodictyon crassifolium). This drought resistant species is an ideal landscaping shrub for southern California.

  Another Species Of Yerba Santa In San Diego County  

Poppy Family (Papaveraceae)

Matilija poppy (Romneya coulteri). Two species of this beautiful shrub are native to southern California, R. coulteri and R. trichocalyx. Cultivated matilija poppies are often hybrids of these species. The large white petals and central mass of bright yellow stamens have been compared with a fried egg. This striking shrub is eagerly sought after by gardeners in Europe. According to the Jepson Manual of California Plants (1996), this plant produces the largest flower of any plant native to California. I would definitely consider the blossom of jimsonweed (Datura wrightii) a close rival in size.

See Blossom of Jimsonweed (Datura wrightii)
See The Yellow Bush Poppy (Dendromecon rigida)
  See The Similar Prickly Poppy (Argemone munita)  

Four O'Clock Family (Nyctaginaceae)

Wild four o'clock (Mirabilis californica), a native shrub in the coastal sage scrub.

  The Giant Four O'Clock In San Diego County  

Cucumber Family (Cucurbitaceae)

The massive caudex and spiny seed capsules of wild cucumber (Marah macrocarpus), a native caudiciform member of the gourd family (Cucurbitaceae) that climbs over shrubs of the coastal sage scrub adjacent to the Arboretum. The entire caudex was about 2 feet (0.6 m) long and weighed approximately 40 pounds (18 kg). I have seen other specimens in the wild that were three times this size. This is one of the first species to resprout after brush fires, particularly during the rainy season of early spring in southern California. Unlike edible fruits of the gourd family called pepos, the wild cucumber is a capsule that splits open at one end.

  See The Wayne's Word Article About The Gourd Family  

Pea Family (Fabaceae)

Deerweed (Lotus scoparius var. scoparius), a native shrubby perennial found throughout the Palomar College Arboretum and adjacent coastal sage scrub. Much to the chagrin of botanists like myself, this genus has been renamed and the new scientific trinomial is Acmispon glaber var. glaber. In the desert var. brevialatus, the keel is longer than the wings.


  1. Cladonia chlorophaea Gray-green lichen with podetia
  2. Diploschistes scruposus Grayish white lichen


  3. Candelaria concolor Lemon-yellow lichen on shrubs
  4. Flavoparmelia caperata Gray foliose lichen on shrubs
  5. Flavopunctelia flaventior Greenish foliose lichen


  6. Acarospora bullata Brown rock lichen
  7. Acarospora socialis (A. schleicheri) Yellow rock lichen
  8. Buellia pullata See Identification of Buellia pullata
  9. Caloplaca bolacina Orange rock lichen
  10. Dimelaena radiata Gray rock lichen
  11. Verrucaria nigrescens Pyrenocarpous black rock lichen
  12. Xanthoparmelia cumberlandia Foliose rock lichen
  13. Xanthoparmelia mexicana Foliose rock lichen


  14. Calvatea gigantea Giant Puffball
  15. Cyathus olla Bird's Nest Fungus
  16. Geastrum sp. Earth Star
  17. Lysurus cruciatus Lizard's Claw Stinkhorn
  18. Tulostoma brumale "group" (cf. T. berteroanum) Stalked Puffball
  Wayne's Word Lichen Links  
Wayne's Word Fungus Links
Unusual Bird's Nest Fungus

Coastal Sage Scrub In Baja California

In the coastal sage scrub south of Ensenada, Baja California there is an interesting endemic species of buckeye (Aesculus parryi). Like other species of shrubs in this plant community it is drought deciduous, but this one has showy leaves that turn gold during late spring and early summer. This picture was taken near the turnoff leading east into the Sierra San Pedro Martir.