VI. PLANT COMMUNITIES

A plant community is a recognizable and complex assemblage of plant species which interact with each other as well as with the elements of their environment and is distinct from adjacent assemblages. A plant community is not a static entity: rather it may vary in appearance and species composition from location to location and also over time. What makes each of these communities distinguishable to us is its general physiognomy or physical structure. This overall appearance is created by the particular species present, as well as their size, abundance, and distribution relative to one another. Dominant species, those whose presence most influences the community environment and composition, are often the largest or the most abundant and may be a single species or several codominant species. Dominance may also be sociologic, expressed in the form of allelopathogens, chemical compounds manufactured by some plants that inhibit the growth and development of other species and/or seedlings of the same species within a certain distance. Community structure and distribution are dictated by the delicate balance of environmental factors: soils, climate, topography, geography, fire, time, and humans and other living beings.

Plant communities may occur as relatively obvious ribbons across a landscape, such as the lush green path of a river through the desert. More often, however, adjacent communities interdigitate, their boundaries less distinguishable. Ecotones are areas where adjacent plant communities overlap with, transition, and grade into one another and have a unique set of characteristics which are defined spatially, temporally, and by diverse interactions among the adjacent communities. Earlier literature referred to these conspicuous components of the landscape as "edge" or "margin" habitats, and numerous current studies focus on the "edge effect" and "landscape boundaries." Ecotones vary in size and species composition, containing elements of each of the bordering communities. They may be predictable and recognizable entities whose physiognomy and even species composition may be similar from one geographical area to another. In other instances, the boundary between communities may be a band of barren soil caused by animal browsing or by phytotoxins (plant-produced allelopathogens), for example, between the grassland and the black sage (Salvia mellifera)-dominated coastal scrub on several hillsides of Poly Canyon. Where chaparral and coastal scrub adjoin in the Canyon, the ecotones vary in proportion, probably most directly as a result of varying soils and topography. Another example is on steep slopes above Brizzolara Creek. Where coastal live oak woodland and riparian communities meet, ecotones can be quite broad. This makes it very difficult to tell exactly where one community ends and the other begins. Regardless of their scale, "ecotones have important characteristics... and play an integral part in the behavior of the landscape as a whole." Whatever characteristics specific ecotones may have, this report will be limited to the broader categorization, plant communities.

Communities vary over time. Fires, floods, grazing, and plowing are some disturbances which quickly change a community. As the vegetation returns to a disturbed area, it may represent the same species that were there before, or other species may invade the area. This change in communities is called succession. Natural ecological succession tends to proceed at a relatively gradual pace, sometimes taking hundreds of years. During this time, communities evolve from one to another, through a series of seral (temporary, non-climax) stages. Eventually, in the absence of further disturbance, a climax community develops, one which is at equilibrium with the environment. In Poly Canyon, there are areas whose probable climax community is chaparral, but which now are dominated by black sage (Salvia mellifera). Black sage is primarily a component of coastal scrub, but it invades areas previously dominated by chaparral which have burned or have otherwise been disturbed (e.g., in the chamise chaparral that burned in 1975 just north of the 'P').

Just as individual plants and animals are named and sorted into groups of similar types, plant communities are also classified. There are many ways of looking at communities. One can focus on the characteristics of the habitat, such as alpine meadow, where the habitat remains the same although the species composition and physiognomy or community structure may vary from site to site. Another focus is the physiognomy of a community, for example chaparral: dense vegetation of woody shrubs with evergreen hardened leaves and relatively little understory or leaf litter. The species composition varies from locality to locality, but the overall appearance of the community remains the same. A third focus of community classification is the species composition. For example, the sole dominant species of a coastal live oak woodland is the coast live oak (Quercus agrifolia).

Numerous plant community classification systems have been formulated for California, each based on distinct experiences and with differing goals. Four of these most commonly used locally include: Holland and Keil , Barbour and Major , Natural Diversity Data Base (NDDB) Natural Communities Program , and California Native Plant Society. The first two are more didactic and provide a basic understanding of the California flora for the academic community and general public. The second two share the objective of recognition of all natural plant communities and ecosystems and their inclusion in the state data base for the purpose of legally pursuing their protection. With this more holistic approach, the protection of whole ecosytems would reduce the number of state and federal listings while increasing the number of species protected. See Table 10.

The plant communities (per Holland and Keil) found in Poly Canyon are chaparral, coastal scrub, coastal live oak woodland, riparian, grassland, serpentinite, rock outcrop, and anthropogenic (i.e., man-caused, disturbed, or ruderal areas such as roadsides and pastures). A discussion of each of these follows, along with descriptions and illustrations of the dominant and most common associated plant species.

Table 10.
COMPARISON OF COMMUNITY CLASSIFICATION SYSTEMS
restricted to communities observed in Poly Canyon)