Species and Community Profiles - San Francisco Estuary ...

Plants
outside the influence of Sierran gold mining and prior
to extensive diking, were evident in maps of the Bay prepared
in the 1870s (U.S. Coast Survey maps).
Marsh Sediments and Plants – Depositional environments
of tidal marshes in the San Francisco Estuary
are variable and are significant for the distribution
of uncommon plant species. In most of the San Francisco
Estuary, the sediments of the middle-marsh marsh
plain consists of bay mud (fine silt and clay) with significant
percentage of organic matter in mature marshes.
Local coarse sediment deposits, often beach ridges
(marsh berms, or marsh-beach ecotones) composed of
sand, shell fragments, organic debris, or mixtures, create
physically mobile (periodically eroded and redeposited),
well-drained high marsh habitats with affinity for
some common high marsh species (e.g., Grindelia stricta
var. angustifolia, gumplant) and probably also species
now locally extinct or rare, such as Suaeda californica,
Atriplex californica (California saltbush), and Castilleja
ambigua (salt marsh owl’s clover or Johny-nip). Marsh
berms are associated with relatively high wave energy environments
in the Estuary, located near coarse sediment
sources such as eroding bluffs, submerged fossil sand and
shell deposits, stream mouths, and eroding marsh edges.
Such features were commonly represented on U.S. Coast
Survey maps of the mid-1800s, but persist today in very
few localities of the Estuary (e.g., Point Pinole, Redwood
City area, San Leandro area, and northern San Francisco
peninsula). Similar coarse-sediment features probably occurred
as natural levees of upstream reaches of large tidal
sloughs with significant coarse sediment loads, as is observed
today in Morro Bay. Alluvial fans also create
gradually sloping ecotones with uplands, with variably
textured sediments and freshwater runoff and seeps. Few
small alluvial fans exist at tidal marsh edges of the Estuary
today (e.g., Point Pinole, Whittell Marsh), but were
historically abundant in parts of the Estuary, supporting
diverse ecotonal plant communities (Cooper 1926).
Analogous alluvial fan-tidal marsh ecotones occur in
maritime salt marshes of Point Reyes and Tomales Bay
areas, where they support distinctive local plant assemblages,
including uncommon to rare species.
Peter Baye
Regionall rare salt marsh owl’s clover, or Johnny-nip
(Castilleja ambigua ssp. ambigua). (Tidal marsh,
Whittell Marsh, Point Pinole)
10 Baylands Ecosystem Species and Community Profiles
Comparison With Other Estuaries – The tidal
marshes of the San Francisco Estuary are the most extensive
on the central coast of California, and their plant
communities are distinct from other central coast tidal
marshes in many respects. Most other large central coast
tidal marshes are associated with shallow embayments
with large open tidal inlets (e.g., Tomales Bay, Drakes
Estero and Bolinas Lagoon in Marin County; Bodega
Bay in Sonoma County; Elkhorn Slough in Monterey
County; Morro Bay in San Luis Obispo County) which
impose strong marine influence on the character of their
sediments, salinities, and vegetation. Central coast tidal
marshes tend to be isolated and few because of the steep
modern shoreline with few valleys or wave-sheltered
bays. These tidal marshes have extensive sandy substrates,
relatively small, local inputs of fine sediment and
freshwater discharges and brackish (mesohaline) conditions,
and are inundated by water approaching marine
salinity (34 ppt) during most of the growing season.
Some tidal marshes associated with stream mouths have
relatively more freshwater influence and brackish marsh
vegetation (e.g., pre-historic Elkhorn Slough and Salinas
River, Monterey County; Russian River estuary,
Sonoma County), but in association with seasonal reduction
in tidal influence because of partial or complete closure
of coastal inlets at river mouths (dammed by sand
beach ridges during periods of relatively low river discharge).
In contrast, the tidal marsh plant communities
of the San Francisco Bay Estuary developed under conditions
of abundant and predominantly fine sediment
(bay mud, clayey silts and silty clays with high nutrientholding
capacity), relatively large tidal range, and extensive
brackish marshes associated with relatively large
freshwater discharges, distributed over broad, fluctuating
salinity gradients (Atwater et al. 1979)
Historically, salt pans (unvegetated, seasonally inundated
depressions or flats within the tidal marsh) and
local salt ponds (perennial deposits of crystalline salt in
hypersaline ponds) were well-developed in San Francisco
Bay tidal marshes (U.S. Coast Survey T-charts, 1850s),
supporting distinctive vegetation (widgeongrass, Ruppia
maritima, in some pans) or microalgal floras (in salt
ponds). Pans are relatively infrequent in other central
coast tidal marshes compared with the historic conditions
of the San Francisco Estuary, and natural salt ponds
were not known to occur in other central coast tidal
marshes. Today, edges of high marsh pans are associated
with at least two regionally rare species (Cordylanthus maritimus
ssp. palustris and Castilleja ambigua ssp. ambigua),
and may have been associated with many others in the past
(e.g., Lepidium latipes, L. oxycarpum; Table 1.3)
Tidal Marsh Plant Communities
The distribution of tidal marsh plants is strongly (but
not exclusively) influenced by tidal elevation and salin-