chamise; Photo by Ellen DeanThree types of chaparral occur within the Reserve: the Chamise, Chamise - Wedgeleaf Ceanothus, and Scrub Interior Live Oak Alliances. Although these grade into one another, in general the north and east-facing slopes and ridge tops support the more speciose scrub oak chaparral. The same areas support chamise - wedgeleaf chaparral on southerly and westerly trending slopes, and pure chamise is found on ridgetops and south and west slopes.

Although all of these communities tend to occur in xeric areas, pure chamise (Adenostoma fasciculatum) claims the driest areas (12.5%). Chamise has needle-like leaves that are extremely drought resistant. It is well-adapted to fire by its ability to resprout very quickly from the root crown as well as to reproduce prolifically from seed. The area of the Reserve that burned in 1992 shows little sign of disturbance in 2004.

With a canopy comprising 70-80% cover and very little understory, it is the least diverse community on the Reserve. The lack of understory plants beneath chamise has been attributed to a variety of causes over the years, including allelopathic exudates from the chamise36, lack of seed sources39, low moisture and nutrient levels as a result of competition with chamise roots33, and herbivory by mammals32, 35, 38. Many of these factors play a role in the scarcity of understory cover, but the most compelling seems to be herbivory. The dense thicket of shrubs provides cover for rabbits and many small rodents that harvest and eat whatever grasses and forbs manage to germinate near the canopy.

Scrub oak chaparral (9.2%) contains a mix of several species in various proportions. As the name implies, two major components of this community are the shrub form California Bay; Photo by Ellen Deanof interior live oak (Quercus wizlizeni var. frutescens) and the scrub oak (Q. berberidifolia). Especially attractive in the spring, this superalliance also includes flowering ash (Fraxinus dipetala), toyon (Heteromeles arbutifolia), California bay (Umbellularia californica), California buckeye, birchleaf mountain mahogany (Cercocarpus betuloides), and pitchersage (Lepechinia calycina), all twined with wild virgin’s bower (Clematis lasiantha). The species composition appears to be related to aspect and moisture availability.

Diogenes’ lantern; Photo by Ellen DeanThe understory of the scrub oak chaparral harbors a mix of small forbs, lilies, and ferns. Twining brodiaea (Dichelostemma volubile), Diogenes’ lantern (Calochortus amabilis), shooting star (Dodecatheon hendersonii), hedge nettle (Stachys ajugoides), and goldback fern (Pentagramma triangularis) are some of the natives in this diverse understory.

In many areas scrub oak chaparral interdigitates on the ridges with the Chamise - Wedgeleaf Ceanothus Alliance, which comprises 7.2% of the Reserve. In general on the northwest-southeast trending ridges on the west side of the peninsula, the scrub oak occupies the north and east facing slopes, and the chamise - wedgeleaf ceanothus the south and west facing slopes. In this community, as depicted on the map, the co-dominants appear to be a variety of shrubs including scrub oak, toyon, ceanothus (Ceanothus oliganthus), birch-leafed mountain mahogany, and interior liveoak. Wedgeleaf ceanothus (Ceanothus cuneatus) is uncommon.

Photo Credits: Title, Ribes malvaceum (Dan Tolson), chamise, California Bay, and Diogenes’ lantern (Ellen Dean). For more pictures see: http://elib.cs.berkeley.edu/photos/flora/

This page last updated: March 21, 2011  


Contact: Dr. Virginia Boucher
John Muir Institute of the Environment
109 The Barn, University of California, Davis, CA 95616
Phone: 530-752-6949; email: vlboucher@ucdavis.edu

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