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Habitat Info
What ecological function do vegetated flood control channels serve?
They allow nature to exist in urban areas. For example, Glendale Narrows
supports a vibrant riparian plant and animal community.
What is growing in these channels?
The non-concrete portions of the river currently support three main
types of habitat, Freshwater Marsh, Riparian Forest, and Alluvial Scrub.
Freshwater Marsh is a herbaceous community of reeds, sedges, and grasses
that grows with abundant surface water. Riparian forest consists of
a distinctive set of trees (including willow, alder, sycamore, & ash)
and shrubs, particularly Mulefat. Both habitats are "wetlands", and
develop quickly where water is and concrete isnÜt. Alluvial Scrub is
a desert-like plant community restricted to boulder-strewn areas of
Big Tujunga Wash upstream of Hansen Dam. Other examples of this habitat
in Los Angeles Co. may be found along the San Gabriel River above Santa
Fe Dam and along the Santa Clara River in Santa Clarita.
Are these habitats natural?
Yes. Much of the San Fernando and San Gabriel Valleys were Alluvial
Scrub prior to their agricultural development. Riparian Forest was extensive
along the L.A. River and tributaries from the north base of Griffith
Park south to Long Beach, and pockets of Freshwater Marsh dotted the
L.A. basin, especially in what is now called the South Bay.
Do todayÜs versions of these habitats look anything like the original
one?
Yes, but on a much smaller scale. Non-natives have become a persistent
problem, however. Arundo donax is an giant grass that was introduced
into the area from Eurasia, and because the native riparian plants are
not adapted to compete with it, it has overrun many of our lowland waterways.
Arundo supports almost no native animals, and is a major threat
to the L.A. River.
Where are the most biologically important riparian areas of coastal
L.A. County?
Most crucial for protecting rare flora & fauna are the free-flowing
(unchannelized) streams, such as the Santa Clara River and Big
Tujunga Wash. Also important are catchment basins behind dams (Hansen,
Van Norman, Sepulveda, and Whittier Narrows), which support large areas
of riparian and wetland habitat. The soft-bottomed portions of the concrete
channels sustain native flora and fauna within the L.A. Basin, but are
of limited value in supporting riparian communities due to their small
size.
Summary of FLORA AND FAUNA of the Los Angeles River
Sources:
Garrett, K.L., ed. 1993. Biota of the Los Angeles River. Los Angeles County
Museum of Natural History.
Swift, C. 1993. The status and distribution of freshwater fishes of southern
California. Bull. Southern California Acad. of Sci. 92(3):101-167.
Birds
341 species have been recorded in the river and tributaries, which
is 3/4 of all bird species in L.A. County.
In 1993, a survey conducted by the L.A. County Museum of Natural History recorded 116
species of birds along a three-mile channelized
section of the river through Glendale/Los Feliz. This area features
concrete levee walls and a narrow strip of riparian woodland along the
channel.
Declining bird species such as the Least BellÜs Vireo (Federally Endangered)
require riparian habitats in Southern California for their survival,
and use the L.A. River and its tributaries for nesting and raising young
in the Spring. Important areas for breeding riparian birds include the
entire Sepulveda Basin Recreation Area and the Hansen Dam/Big Tujunga
Wash. Others birds, such as Lazuli Bunting and LincolnÜs Sparrow, rely
on riparian vegetation for food and shelter during migration and/or
Winter.
Plants
60 species of native plants were identified by the Biota of the Los Angeles River
study growing
in the channelized portion of the Los Angeles River. Several are found
nowhere else on earth than in alluvial wash habitat of Southern California,
such as along Big Tujunga Wash.
Fish
Southern California boasts a highly endemic native fish fauna (most
species found nowhere else on earth). Of only 7 native freshwater fish
species known from the Los Angeles River watershed, 2 remain in the
L.A. Basin, Arroyo Chub and Santa Ana Sucker. These are strongly dependent
on the remaining riparian vegetation in the L.A. River and its tributaries.
Currently, the only known viable fish habitat in the Basin is soft-bottomed
stretches within Sepulveda Basin and along Big Tujunga Wash behind Hansen
Dam. More suitable habitat exists above the floor of the Basin (e.g.
Upper Big Tujunga Ck., which supports a third species, Santa Ana Speckled
Dace) and within the Simi Hills west of the San Fernando Valley. Both
the chub and the sucker could be reintroduced in portions of the River
with "moderate" improvements in water quality (according to Garrett
1993), and, presumably, a reduction in disturbance to the riparian habitat.
Reptiles / Amphibians
Aside from Big Tujunga Wash, which still preserves a fairly complete
native reptile and amphibian community, Pacific Slender Salamander,
Pacific Tree Frog, Western Toad, and 9 species of lizards and snakes
are believed to persist along the channelized portions of the river.
Undoubtedly, many species fall into the river and are washed downstream,
providing a ready source of recolonization.
Mammals
The LACM study recorded 10 native species of mammals using Big Tujunga
Wash. Other areas where native mammals (e.g. Black-tailed Jackrabbit)
may be found along the river within the Los Angeles Basin are within
the Sepulveda Basin and in a small series of grassy fields near Carson,
most of which are slated for development.
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