I’ve just returned from a spring break jaunt to one of my favorite places in California – the coastal dunes of central California. While attending Cal Poly, I spent three years wandering the coastal dunes, pygmy oak forests, and coastal chaparral of San Luis Obispo County, especially Montana de Oro State Park. This year’s trip was a chance to introduce my son to the dynamic scenery and biodiversity that can be witnessed along the California coast. San Franciscans are indeed fortunate to have access to some splendid examples of this coastal legacy, which is so characteristically Californian. I’ve written about our coastal dunes in past newsletters (see the article on dune gilia, vol. 11, no. 2, June 1997), describing the former extent and glory of the San Francisco dunes. This article is dedicated to the remaining dune scrub habitat in San Francisco and the herculean efforts underway to restore and preserve this habitat and the rare species still to be found there.

In California, our coastal dune systems are associated with the mouths of rivers passing through the Coast Ranges. Key elements in the formation of coastal dunes are a sediment source and a shoreline perpendicular to the prevailing winds. A typical cross-section of a sandy central and northern California coastline, beginning at the water’s edge and moving downwind, might include the following distinct zones: beach, foredune complex (primary foredunes, dune hollows, dune mat, foredune ridge); moving dunes (sand sheet, transverse dune, dune blowouts); dune slack ponds and lakes; and stabilized, vegetated dunes. It is this latter zone where we find coastal dune scrub habitat. Dune scrub varies in species composition between southern, central, and northern parts of the state. Central dune scrub, which extends from Bodega Bay to Point Conception, consists of a dense cover of scattered shrubs, subshrubs, and herbs, generally less than three feet high. It is restricted to stabilized backdune slopes, ridges, and flats.
San Francisco’s sand dunes are a relatively recent addition to the landscape, having appeared in the last 10,000 years as the sea level was rising. Prior to development, San Francisco’s western side once supported as much as 14 square miles of dune scrub habitat. Unfortunately, there are only three published accounts of the San Francisco dune vegetation (Ramalay 1918, Reynoldson 1938, and Kaufeldt 1954), providing little more than a snapshot of the habitat. The latter study was conducted literally just ahead of the bulldozer, as the final portions of open dune in the Sunset District were about to be developed.

Dunes at Fort Funston, 1937This photo shows the future site of Battery Davis, at Fort Funston, in 1937. The photo was taken from a long-vanished hilltop somewhere close to Skyline Boulevard at approximately the location of today’s entrance road. It clearly shows the original hilly terrain of south Fort Funston as well as the groundcover and vegetation spread. This is just one of several hundred photos taken by the Army Corps of Engineers. Among other topics, the photos document the construction of Battery Davis from the survey stage to final transfer. Although most photos show close-up construction details, dozens and dozens of the pictures contain landscape views of the construction site that are invaluable for research. Actually, the original pictures in this Corps of Engineers collection aren’t really photos. They are 8″ x 10″ negatives, so their detail is exquisite.

Coastal dunes are by their very nature dynamic. The effects of wind and water and the addition and removal of sediment result in a constantly shifting, eroding, and self-renewing ecosystem. It’s really quite magical. The real wonder, however, is the biological diversity such an ecosystem supports. But this dynamic nature makes the dune system highly vulnerable to subtle (and not so subtle) alterations. Development aside, the biggest threat to coastal dune habitats is invasive non-indigenous species. The spread of invasive species has been called one of the most serious threats to natural plant communities on the planet (Heywood 1989, Cronk and Fuller 1995). Once they get a toe-hold in a natural plant community, invasive non-indigenous species result in a decline of the populations of native species and a simplification of the ecosystem, causing a tremendous drop in biological diversity. Nowhere is this more apparent than right here in our own backyard. Plantings of Monterey cypress and Monterey pine (native to California, not native to our stretch of the coast), the dreaded Hottentot fig (a.k.a. ice plant), and, of all things, European beach grass all can replace a hundred or more species of native plants on which innumerable birds, butterflies, and beetles depend.

Efforts to restore native dune habitats are costly, tiring, and, in some cases, thankless work. The controversy surrounding the removal of trees (the charismatic “mega-vertebrates” of the plant world) summons up strong emotions. It’s very difficult to envision the end product without having observed it, in all its glory. Summer is a wonderful time of the year to do just that. Even on a cold, foggy June day, stand among dunes (stick to the trails, please) and soak up the tranquility. On sunny days, let your eyes absorb the different shades of gray and green.

Remnants of San Francisco’s coastal dune scrub habitats can be found at the Presidio at Feral Dunes, Lobos Creek Valley, North Baker Beach, Crissy Field, and Presidio Hills. Another nearby locale is Fort Funston. To learn more, visit the Presidio Nursery web page. See the Presidio Nursery Volunteer Program for opportunities to volunteer on one or more of the habitat restoration efforts ongoing around your city.

Common & rare plants in SF’s dune scrub.

References:

Cronk, Q.C.B., and J.L. Fuller. 1995. Plant Invaders: the Threat to Natural Ecosystems. Chapman and Hall. New York. 241 pp.

Heywood, V.H. 1989. “Pattern, Extent, and Modes of Invasions by Terrestrial Plants.” Pages 31-60 in J.A. Drake et al., eds. Biological Invasion: a Global Perspective. John Wiley and Sons, New York.

Kaufeldt, Carlos E. 1954. “Observations on San Francisco’s last major sand dune, with notes on its flora and insect fauna.” Wasmann Journal of Biology 12(2):293-325.

Ramaley, F. 1918. “Notes on Dune Vegetation at San Francisco, California.” Plant World 21:191-201.

Reynoldson, W.F. 1938. The Flora of San Francisco Sand-Dunes, its Composition and Adaptations. M.S. Thesis, University of California, Berkeley. 57 pp.