Coastal scrub communities are characterized by low shrubs and an absence of trees. Types of shrubs include either pure stands, or mixtures of low, thick-leaved evergreens and coarse, deciduous species that drop their leaves in response to periodic drought conditions. Three representative scrub assemblages (not strictly limited to the coast) are the northern coastal scrub, southern coastal sage scrub or soft-chaparral, and arid hard-chaparral.
Low shrubby overstory and lush herbaceous undergrowth often characterize the northern coastal scrub community, which may grade into adjacent coastal prairie. Many northern scrub species retain their leaves throughout the year. Native coyote brush, Baccharis pilularis, is the most abundant plant in this community and is easily identified by its white fall flowers. California blackberry, Rubus ursinus, and poison oak, Toxicodendron diversilobum, are other common shrubs. The predominantly gray-green northern scrub landscape is accented by colorful monkeyflowers, Mimulus spp., and tall cow parsnip, Heracleum lanatum, with its characteristic yellow-green foliage and flat, slivery-white flower clusters.
In contrast, the more arid and gravelly soils along the southern coast support mostly drought-adapted shrubs with few or no understory species. This is the southern coastal sage scrub, or soft-chaparral, community named for the ubiquitous black, purple, and white sages, Salvia spp. Sage scrub communities are easily identified by their characteristic fragrance and long flowering season, which may extend over half the year. Ecological adaptations include the production of two sets of leaves. In sages, the larger leaves fall off during the dry summer season, reducing evaporative water loss, while the smaller ones remain intact. Other species, such as deerweed, Lotus scoparius, drop their leaves completely. Sage ensures its success as a dominant community member by releasing chemical compounds into the soil that prevent other plants from establishing themselves. This is called allelopathy. Additional inhabitants of this community include California sagebrush, Artemisia californica; lemonadeberry, Rhus integrifolia; and poison oak.
Hard-chaparral is a scrub community unique to California and southwestern Oregon. It occurs in drier regions characterized by mild, wet winters and very hot summers. In the northern part of the state this community occurs inland, but in the southern Coast Ranges it is contiguous with sage scrub community. Hard-chaparral shrubs can form dense, impenetrable stands of a few species, or diverse species assemblages. More than 900 plant species have been found in association with different chaparral communities. Common inhabitants include chamise, Adenostoma spp.; California lilac, Ceanothus spp.; and manzanita, Arctostaphylos spp. Fire is an important ecological factor in maintaining hard-chaparral communities because, among other things, it helps to cleanse the soil of allelopathic compounds and clear space for new and different plant species.