Ballona wetlands - A
COMPLEX MOSAIC
Ballona contains a complex mosaic of habitats defined
mainly by hydrology, including wetland habitats, such as brackish and
freshwater marshes, seasonally flooded freshwater wetlands, salt pans, riparian
and upland habitats, like coastal sage scrub and sand dunes. Many wildlife
species, especially birds, utilize more than one habitat type – thus the
juxtaposition of these habitats next to one another, also known as
heterogeneity, which is important for biodiversity.
Estuarine and
Brackish Marshes
At the heart of the Ballona Wetlands is the coastal
salt marsh or estuary, the crown jewel of current restoration planning.
Estuarine marshes, the historically dominant habitat type of the Ballona
Wetlands Ecological Reserve (BWER), require oceanic tidal influence.
Under natural
conditions, tidal movements, along with variations in freshwater flow coming
from inland, create complex and ever changing environmental gradients of
topography, moisture, temperature, and salinity that enable many kinds of
organisms to find their own particular place. As a result, coastal salt marshes
are one of the most biologically diverse and productive habitats in the world.
When Ballona Creek was channelized, the BWER was cut off from
this necessary disturbance regime.
After tide gate
installation in 2004, the western and southern portions of Area B (see map
below) began to reflect estuarine conditions, at least
hydrologically. However, species diversity has yet to recover. About 26%
of historic species have not been seen since the 1930s, including coastal dunes
milk vetch and Pacific silverweed, and many others are only present in
superficial amounts.
The majority of the BWER is dominated by non-native and
invasive weeds. Low native diversity is due to restricted tidal influence,
unnatural elevation, farming, oil drilling, and other disturbances. These
conditions will change when restoration plans are implemented. Narrow tidal
channels, which are artifacts of past disturbance and attempts to drain the
marshes, affect the distribution of estuarine habitat. Pickleweed, a high marsh
species, is the dominant and most recognizable salt marsh plant. You can read
about the other plants at Ballona here.
Salt Pan
Area B also
contains salt pans, relatively flat depressions which can be flooded with salt
water during high tides, or become ponds during the rainy season. Salts in
the clay soil leach out to the surface, and over time these salts accumulate,
leading to exceptional saline conditions when water is present and a white hue
on the dried soil. Hundreds of birds can be seen flocking to these salt
pans when ponds have formed after rains or high tides. This habitat is
naturally lacking in vegetation cover.
Freshwater Marsh and Riparian Habitats
The Freshwater
Marsh is located southwest of the intersection of Lincoln and Jefferson
Boulevards, adjacent to the Ecological Reserve. Apart from riparian, this
constructed wetland is currently the only major freshwater habitat at Ballona,
representing a small fraction of a much more extensive freshwater wetland that
once existed before Ballona and Centinela Creeks were channelized, primarily
east of Lincoln Blvd. Historically, the creeks would have released water into
Ballona’s freshwater wetlands, which then would have connected to brackish
marshes leading to the mouth of the estuary and the Pacific Ocean.
Since
construction was completed in 2003, the habitat has attracted more than 250
species of birds, some of which are now returning every year to nest after more
than a 70-year absence. The marsh receives water from the riparian corridor and
runoff from surrounding streets and landscape. The freshwater marsh releases
water into Ballona Creek and some spills over into the southern part of Area B
of the BWER during heavy rains. With restoration more water will be released
into the BWER.
Riparian habitat
is defined by a freshwater stream or presence of fresh groundwater within reach
of plant roots. Riparian habitat at Ballona consists of a corridor along
the base of the Westchester Bluffs and the south edge of the BWER. This habitat
represents a small fraction of what must have been present before Centinela and
Ballona Creeks were channelized. Historical records show the riparian
habitat dominated by alder trees. Currently, most of the riparian habitat consists
of willows. Freshwater marsh and riparian habitats are characterized by
water-loving plants, such as mulefat, cottonwood, sycamores, cattails, bulrush,
and many more.
Seasonal Wetlands
Seasonal
wetlands are valuable habitats that provide additional foraging space
and wintering grounds for wildlife. Currently, the seasonal wetlands at Ballona
were created by past human disturbance. These wetlands are in areas that
are isolated from stream or tide influence because they are too high in
elevation or have been cut off from natural surface water sources. These
wetlands have formed in small depressions and depend entirely on rainfall as a
source of water. Due to soil salinity, pickleweed (normally a salt marsh plant)
tends to dominate these wetlands. During restoration, many of these areas will
be reconnected to a more consistent water source.
Uplands
Two important
upland habitats exist in and around Ballona, coastal sage scrub, along the face
of the Westchester Bluffs, and coastal sand dunes, located on the west side of
Area B. The dunes have been a major focus of restoration by Friends of
Ballona Wetlands. Preservation of habitat is now entirely dependent on rainfall
and weeding maintenance. Natural forces of wind and water, which shaped
the dunes historically, have been lost. This situation is unlikely to
change in future due to constraints of adjacent development and roads. Most
other upland areas in the BWER have been invaded by non-native species and do
not fit any standard habitat classification. Management and control of
these non-native species, and their replacement with native habitat, will be
one of the goals of restoration.
Habitat Heterogeneity - Important for Wildlife
With the variety of habitats in and around Ballona Wetlands, many species
of wildlife live and visit each year. More than 300 bird species have been
observed at Ballona, about 250 of which are at the Freshwater Marsh and Riparian Corridor. Most of these
bird species depend on more than one habitat type and exemplify the interlinked
nature of the Ballona ecosystem. New birds observed at the Freshwater Marsh
system each season, including species like the least bittern (a State Species
of Special Concern) seen breeding at the Freshwater Marsh, are tantalizing
indications of what is possible when the larger Ballona ecosystem is restored.
To discover more about the wildlife of Ballona Wetlands,
check out the Field Guide
to the Wetlands.
The least tern, an endangered species, needs multiple habitat types as it
forages at the Freshwater Marsh and Ballona Creek during the breeding season,
but raises young on small sandy dunes at Venice Beach more than a mile away.
The least bittern, a State Species of special concern, breeds at the
Freshwater Marsh. In fact the Freshwater Marsh is now providing breeding
habitat for several species, including the least bittern, common gallinule, and
Canadian goose, for the first time in over a century.
Photo credits: Don Sterba & USFWS
The Belding’s savannah sparrow, a State listed endangered species,
forages and breeds primarily in high
salt marsh habitat that is flooded only infrequently by tides or is isolated
from tides.
Great blue herons nest in tall trees in upland areas of Ballona but
forage widely along Ballona Creek as well as in upland habitat.