3.  SETTING (continued)

BIOLOGY - THE FRANCISCAN LANDSCAPE

The Bay Area has long been recognized as an area that contains a high number of native species.  San Francisco comprises an integral component of the Franciscan landscape, a distinct biogeographic area of the northern San Francisco Peninsula that ranges from Montara Mountain and Coyote Point to the Golden Gate.  The Franciscan landscape provided habitat for many species adapted to conditions in northern and southern regions and supported a number of rare and endemic species.

The Franciscan landscape has been broken up into small remnant fragments mainly as a result of urbanization.  Additionally, many of the "natural" areas that remain were converted to non-indigenous conifer and eucalyptus forests. Despite the extent of the changes to these ecosystems, there is a remarkably high diversity of remnant habitats and the persistence of some of the rarest species in the wild. (Top of page)

Vegetation

Historic Vegetation

The extensive area of sand dunes in the western part of the City once supported a sparse cover of sand-adapted shrubs and herbs.  The southern areas near Lake Merced hosted a form of maritime chaparral similar to that found today around Monterey Bay.  More densely vegetated stands of coastal scrub and rich perennial grasslands covered the hilly slopes and summits. Serpentine inclusions within both of these dune fields supported thickets of maritime chaparral dominated by what are now rare manzanitas. In the central southeastern portions of the peninsula, grasslands composed of native annual and perennial species of grasses and forbs likely dominated the hilltops and south-facing slopes.  Freshwater marsh, willow scrub habitat, and fringed back-dune ponds could be found in the western and northeast part of the City. Large expanses of tidal salt marsh were found along the northern and eastern Bay shoreline. Trees were not a conspicuous component of the landscape. Coast live oak and dwarf California buckeye scattered on slopes and California laurels were described as occurring along the northern shoreline in some of the earliest descriptions. (Top of page)

Vegetation of the Significant Natural Areas was mapped and sampled for this project in order to: (1) identify what types of vegetation are present in what amounts, (2) identify the dominant species of each type, (3) guide management recommendations, and (4) provide baseline information in order to interpret future monitoring results.  Reference sites were identified and sampled to guide revegetation activities and determine restoration success criteria.  Significant Natural Area vegetation was mapped as discrete patches based on structural features and on dominant floristic features.

These patches of vegetation were then classified into formations, sub formations, and series. Formations are based on the life form of the dominant species (e.g., scrub - dominated by shrubs, and forest - dominated by trees). Series are based on the identity of the dominant species, and subformations are groups of series that share similar ecological requirements and/or land management histories. Surveys identified 5 formations, 12 subformations, and 101 series. Acreage was calculated by subformation for each site and a total of 1,120 acres, 841 acres containing vegetation, were surveyed and mapped within the Natural Areas.

Vegetation surveys and work conducted by SFRPD staff for other projects resulted in the documentation of 645 species of plants within this area (Appendix C).  These range from the very common blue gum to many species that are known from only one occurrence within the Natural Areas System. Additional species that were not observed during survey work are expected to occur within the Natural Areas. (Top of page)

Herbaceous Formation

There are four herbaceous subformations representing approximately 267 acres or 32 percent of the total vegetated area within the Natural Areas.  Subformations identified include: annual grassland (20 percent), perennial grassland (2 percent), wetland (8 percent), and other herb (2 percent).  The most important series within this formation are the remnant native perennial grasslands and wetlands which are both targets for conservation and restoration. (Top of page)

Scrub Formation

The scrub formation is defined here as vegetation dominated by shrubby (woody, multi-trunked, relatively short) species.  Four subformations are identified: northern Franciscan coastal scrub, central dune scrub, central coast riparian scrub, and non-native scrub. These combine to cover approximately 159 acres, 19 percent of the total vegetated area. Many of the native scrub formations are diverse and structurally complex, making them valuable wildlife habitat. Because of this they are a focus for conservation and restoration.

Mosaic Formation

Seventeen mosaic series were used to describe areas that are too sparsely vegetated with shrubs to be called scrub and yet contain too many shrubs to be called grassland. Eleven of these series, totaling approximately 27 acres, are a combination of an invasive non-native grass or forb with a native shrub.  (Top of page)

Forest Formation

Two forest subformations were used to describe the forest resources of the Natural Areas, native and non-native forest.  Non-native forests dominate this formation and account for 361 acres; over half of this area is blue gum forest.  The native forests are either coast live oak or California wax myrtle forest.  Because high numbers of bird species are associated with oak woodlands, this series is a priority for preservation and restoration.  Non-native forests can provide important habitat for resident and migrant birds.

Other Formation

The Other formation is a "catch-all" category for areas that either are not dominated by vegetation, or are dominated by ornamental plantings.  These areas include open water, open sand, bare ground, developed areas such as buildings, roads, and parking lots, and rock outcrops. Rock outcrops can support interesting and unusual native plants and are considered critical habitat preservation and restoration areas. (Top of page)

Wildlife

Extensive urbanization of the San Francisco Peninsula over the last 150 years has fragmented the wildlife habitat and reduced its quality.  However, in part because plant communities in the Significant Natural Areas are extremely varied, these areas continue to support populations of native animals. Long-term record-keeping has resulted in documentation of 356 species of birds in San Francisco County.  Sixteen species of mammals have been reported from Glen Canyon Park; this list is probably relatively representative of vertebrate species found in most parks throughout the City. Surveys conducted for this project found 11 native reptiles and amphibians and captured 3 of the 6 native rodent species in the City. Additionally, Lake Merced and Sharp Park apparently support small populations of the Federally threatened California red-legged frog (Rana aurora draytonii). Review of background reports indicates that at least 27 species of butterflies have been documented within the City. (Top of page)

Sensitive Species

Fifty-nine species of plants and animals have been designated as sensitive for this management plan.  Sensitive species are defined here as plants or animals that are listed as rare, endangered, or threatened, or candidates for listing, by the U.S. Fish and Wildlife Service, the California Department of Fish and Game, or the California Native Plant Society.  Noteworthy taxa that are uncommon in the City, have range limits in the area, or are especially valuable for wildlife or invertebrates are also included as sensitive species. (Top of page)

LAND USE HISTORIES

Before the San Francisco Peninsula was colonized by humans, its natural landscape was covered by several different types of habitats.  Large portions of the Peninsula were covered by active dune fields including areas that are now portions of the Presidio, Lake Merced, and Golden Gate Park.  More stable areas of soil and bedrock existed in the San Miguel Mountains in mid-Peninsula and supported scrub and oak woodland habitats.  Large areas of wetlands and marshes likely existed along the margin of San Francisco Bay

With the colonization of the area by Native Americans, this habitat pattern changed as seasonal fire was introduced to the upland habitats. The settlement of the area by European peoples resulted in more significant changes to the landscape. Agricultural practices introduced exotic species to the landscape (e.g., wild radish and Italian fennel for culinary purposes and annual grasses as grazing forage) and allowed introduced species adapted to these pressures to expand. General population growth eventually led to urbanization and growth of industry, which in turn resulted in stabilization of the dune fields, filling of the Bay, and removal of much of the native habitats.

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