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Vegetation

The vegetation of the field station has developed through time under the primary control of the factors discussed in under Climate and Geography, that is, climate, substrate, and groundwater regimen. It has been modified secondarily through processes initiated by disturbance, especially fire and off-road vehicle use and, in the eastern part, agriculture.

An aerial view of the field station gives the impression of a mixed but intergrading patchwork of plant cover. The eastern quarter is now occupied by a community composed of both native and non-native species of annual herbs and grasses, providing food and shelter for a number of native animal species not normally found in undisturbed coastal sage scrub. Native shrubs are beginning to recolonize, however, and this area is returning to a Coastal Sage Scrub community, which is the plant community that occupies most of the remainder of the Station.

Coastal Sage Scrub is the dominant vegetation of undisturbed coastal and cismontane valley floors in southern California where the rainfall averages approximately 15' per annum. It is replaced on sites with better water status (usually more upland sites) by either Chaparral or Southern Oak Woodland.

The rather shallow-rooted, only semi-woody shrubs which characterize Coastal Sage Scrub vegetation survive the summer drought by losing most of their leaves and becoming semidormant. This is in contrast to Chaparral shrubs which are evergreen and more deeply rooted, and which continue to metabolize actively through the drought season.

Characteristic Coastal Sage Scrub species at the field station include Coastal Sagebrush (Artemisia californica), White Sage (Salvia apiana), and Flat-top Buckwheat Brush (Eriogonum fasciculatum). Intermixed with these are some evergreen species which are also found in Chaparral — for example, Laurel Sumac (Rhus laurina), Redberry (Rhamnus crocea), and Coffeeberry (Rhamnus californica).

The west central part of the field station supports a grove of Coast Live Oak (Quercus agrifolia) and Sycamore (Platanus racemosa). These, along with Water Wally (Baccharis emoryi), suggest that a permanent ground water source may be closer to the surface here than in other parts of the field station. Given the mixed nature of the underlying alluvial deposits (as discussed above), this seems plausible.

Whether the oaks were once more widespread here, or whether they could become so, is an interesting question. Oak seedlings are slow-growing and notably susceptible to most forms of disturbance including fire, and acorns have low dispersal capabilities. Thus, while adult oaks can weather all but the hottest fires, they do not reproduce well when burning is frequent.

Coastal Sage Scrub species, on the other hand, not only can crown-sprout after burning but produce numerous, light, easily-dispersed seeds which can recolonize burns and reestablish quickly. Thus in a frequently burned area Coastal Sage Scrub will maintain the upper hand even though the area is moist enough to support oaks.

It is difficult to tell the degree to which Coastal Sage Scrub at the field station is successional (i.e., maintained by disturbance). The best present surmise is that most of the area is too well-drained and therefore too dry to support oaks — that is, the depth to the water table is too great. Even in the area where the oaks do occur, oak reproduction appears to be very poor, thus even this patch may not persist indefinitely.

For more information on the flora and vegetation of the field station, see Munz (1974), Barbour and Major (1977), and the references cited therein.

REFERENCES

Barbour, M.G., and J. Major, eds. 1977. Terrestrial Vegetation of California. Wiley, New York. [Claremont Colleges Library holdings]

Munz, P.A. 1974. A Flora of Southern California. University of California Press, Berkeley, CA. [Claremont Colleges Library holdings]