Species and Community Profiles - San Francisco Estuary ...

Plants
Reference Sites
Reference sites for different types of diked wetlands
would generally not be long-lived because of the prevalence
of unstable vegetation conditions in diked Baylands.
Droughts, wet years, changes in drainage and
pumping, disturbances from agricultural practices, and
succession can cause profound changes in vegetation in
short periods of time. The following reference sites reflect
conditions observed in the mid-late 1990s.
1. Diked non-tidal salt marsh (dominant Salicornia
virginica)
Fremont Airport (King and Lyons site; proposed
for phased tidal restoration), Alameda Co.
Gallinas Creek diked wetlands, Marin Co.
Western Marsh and Central Lowlands, Bahia
Site, Novato, Marin Co.
Dredge pond 3E, Mare Island, Solano Co.
Area H, Redwood Shores, San Mateo Co.
2. Diked non-tidal brackish marsh
Cullinan Ranch, Solano Co.
Suisun Marsh managed marshes, Solano Co.
Huichica Unit, CDFG Napa-Sonoma Marsh,
Sonoma Co.
3. Diked subsaline to nonsaline seasonal wetlands
Black Point/Renaissance Faire site, Novato,
Marin Co. (extirpated 1999)
Twin House Ranch Site, Lower Petaluma River,
Sonoma Co.
Leonard Ranch, North Point, Dixon parcels,
Sonoma Co., along Hwy 37
Historic and Modern Distribution
Wetlands of diked Baylands are relatively recent historic
artifacts. The plant associations they support are analogous
to, but distinct from, wetlands along the margins
of historic tidal marshes. Brackish non-tidal marshes
somewhat similar to diked brackish marshes probably occurred
within alluvial deposits at mouths of small streams
which discharged into tidal marshes with locally poor
drainage, such as near Ignacio (Novato), where riparian
areas converged with dense marsh ponds and few or no
tidal creeks. Analogous examples of brackish or subsaline
marshes with marginal tidal flooding are found today
along Drakes Estero and Tomales Bay, particularly
near shallow backbarrier lagoons. Salt marsh with restricted
tidal influence probably occurred along portions
of the Bay where local sand beach ridges were likely to
obstruct tidal flows. One modern example exists at Pinole
Point (Whittell Marsh), where the proximal end of a
sand spit episodically dams small tidal channels, causing
seasonal ponding in a small salt marsh cut off from
regular tidal flows. Prehistoric examples of “ pocket”
nontidal salt marsh probably occurred in the vicinity of
Richardson Bay, Alameda, Oakland, and the San
40 Baylands Ecosystem Species and Community Profiles
Francisco Peninsula, where sand beach ridges occurred.
Seasonal freshwater wetlands (vernal pools and
swales, springs) occurred within grasslands peripheral to
the Bay, particularly in the Petaluma River valley, on alluvial
terraces near Fremont, portions of Richmond and
Berkeley, and along much of the Suisun Marsh area.
Their distribution and abundance, as suggested by soil
surveys, were probably not limited to areas mapped as
poorly drained; seasonal freshwater wetlands often occur
as local inclusions within soil series in which wetlands
are not indicated as prevalent. This is indicated by
records of vernal pool endemics in locations like San
Francisco, where “ vernal pool” soil types are not mapped,
but winter pools with typical endemic annuals were
found.
The historical abundance and distribution of these
wetland types is extremely difficult to quantify in terms
of area. Quantitative estimates of historic abundance of
seasonal wetlands displaced by urbanization depends
heavily on interpretation and assumptions about early
soil surveys (which were not intended to function as
maps of actual or potential native vegetation), historical
accounts, and fragmentary information on species occurrences
in old floras. The qualitative differences in natural
non-tidal wetland types and their diked Bayland analogues
further obscures the relevance of quantitative
comparisons between historic losses of natural seasonal
wetland plant communities and their partial replacement
with wetlands of diked Baylands.
Conservation Issues
Plant conservation needs for diked wetlands are dependent
on larger-scale wetland management and restoration
plans. Diked wetlands usually support less native
plant species diversity than mature tidal marshes at
equivalent locations, but may in some cases still provide
important plant conservation functions. For example, in
San Pablo Bay, agriculture and development have eliminated
most historic natural seasonal wetlands in supratidal
grasslands peripheral to the Bay. The original vernal
pool flora which occurred in subsaline to alkaline
depressions around the historic edge of the Bay (as in
parts of northeastern Suisun Marsh today) has been
largely extirpated in its original location, but persists in
artificial equivalent topography and edaphic conditions
in some diked seasonal wetlands. These populations
maintained in subsaline conditions may provide important
founder populations for opportunities to restore
vernal pool and swale systems in the original soil types
and topography along the margins of the Bay, in coordination
with tidal restoration. Similarly, one diked salt
marsh in the South Bay (former Fremont Airport) provides
refugia for Suaeda moquinii, otherwise found
around the Bay only in remnant alkali vernal pools ad-