An Endangered Ecosystem
Mediterranean ecosystems like ours exists on less than 3% of the earths land surface. The only other places it occurs are in coastal zones along the Mediterranean Sea, parts of Western & Southern Australia, the Chilean Coast and Capetown South Africa.
Worldwide, the Mediterranean ecosystem is more threatened than the rainforest. Conservation International has declared our local ecosystem, the California Floristic Province, one of the world’s top 10 “hotspots” of biodiversity. They estimate that only 25% of the original habitat area remains. Some of the now-rare habitats include riparian woodland, willow thicket, mulefat scrub, coastal sage scrub, valley oak savanna and native grasslands.
Our region was once covered with native plants and animals that evolved over millions of years to be perfectly adapted to our Southern California's cycles of drought and flood. Of the 4,426 vascular plants found here, 2,125 species (48 percent) are found nowhere else in the world. There are more plant species in this small area than in the whole central and northeastern United States combined. More species of bird breed in our region than anywhere else in the country.
Environmentally, the Los Angeles River is presently a shadow of its former self, but areas of great beauty still exist. Channelization removed most of the river’s vegetation, wetlands, wildlife, and ecological richness.However, high water table in the Sepulveda Basin, Glendale Narrows and Compton Creek made it impossible for the river bottom in these areas to be sealed in concrete, preserving a portion of the river’s natural bed. In the 51 miles of the Los Angeles River, 13 miles retain their natural riverbed. Since the passage of the Clean Water Act, these sections have once again flourished with wildlife. These remaining soft-bottom sections of the river may provide the only native habitat for miles around.
For example, Compton Creek is located in one of the most densely populated areas of Los Angeles County and the United States. The creek’s 2.5 soft-bottom miles closest to its confluence with the Los Angeles River are teeming with life. The scarcity of other habitat and the location between other flyways increases the biological and ecological value of this small section of creek.
Within the Sepulveda Basin, more than three miles of nearly undisturbed, natural river pass through a regional recreation area and a 225-acre wildlife reserve. Further downstream between Burbank and the Arroyo Seco in the Elysian Valley, the river has concrete walls and a soft bottom. Native and non-native trees grow in the soft bottom of the channel. Mallards, teals and coots nest on the islands of rushes, reeds, willows, and grasses. Here great blue herons, hooded merganser, kingfishers, red-tailed hawks and kestrels rest and feast on the crayfish and fish within the river.
Much of the remnant natural habitat within the Los Angeles River and its tributaries has become reestablished as a result of neglected "maintenance", where the former “scorched earth” policy of scraping our waterways was made difficult after the passage of the Federal Clean Water Act in 1972. This allowed bits of natural habitat to reassert themselves in urban areas. Stands of willows draw songbirds during seasonal migration. Sparrows and finches nest and feed in the native scrub communities of the soft bottom. Habitat has developed in the lower estuary where algae growth encourages invertebrate life, which provides food for shorebirds during the migratory seasons in spring and fall.
The Santa Clara River still maintains it’s natural processes and abundant habitat. It is a rich, living example of what we have lost on the Los Angles River. The Los Angeles River is the cautionary tale for the Santa Clara, where planners are today making decisions about the river's future. The opportunity exists there to forge a new path, keeping development out of the river's natural floodplain and preserving its natural function and habitat diversity.
A paradigm shift has begun in our approach to managing stormwater. We have begun to realize that by removing nature’s ability to capture and cleanse urban runoff, we have contributed to increased pollution in our oceans and deprived ourselves of a cost-free source of drinking water. Over 60% of our urban landscape has been paved, greatly altering the functioning of our watershed. Prior to 1960, 80% of rainwater in the LA River watershed would percolate into the ground. Today that figure is closer to 8%, with the rest draining out to the sea. By percolating more rainwater into the aquifer, we create less strain on the river system and more local drinking water supply. By increasing open space in the region, we can begin to move over time toward a balance that will allow more “green engineering” of our rivers. Bio-engineered bank stabilization uses living native plant materials rather than concrete to provide structural stability to our riverbanks. These trees and plants provide a healthier environment for people, increase habitat for wildlife, and help to improve water quality. It is a process that will take time, and it will be more feasible in some places sooner than in others, but it is a goal worth working for.
Still, controlling invasive exotic vegetation within the reestablished habitat is an ongoing problem. The rapid spread of giant reed (arundo), castor bean, fountain grass, star thistle, fan palm, shamel ash and mustard displaces the native habitat and disrupts the fragile riparian balance.
If you’d like to create some habitat in your own backyard, consult one of your local native plant resources & nurseries. The Watershed Council's Landscape Ethic Committee has developed a useful list of California Native Alternatives for Common Exotic Ornamental Plants.