Santa Ana River - Ecology

Ecology

Hundreds of species of animals and plants characterize the Santa Ana River's diversity of climates and vegetation zones. There are over ten of these vegetation zones in the watershed—including the sparsely vegetated alpine and subalpine zones in the mountains, mid-elevation forests of pine, lodgepole and oak, chaparral, coastal sage scrub, the increasingly rare riparian forest and marshes along the river bed, lined with trees and rushes, and the thinly vegetated coastal areas virtually flush with sea level. The watershed supports up to 200 bird species, fifty mammal species, 13 reptile species, 7 amphibian species, and 15 fish species, including steelhead trout.

The largest portion of the watershed, the Inland Empire portion, is dominated by a hot, dry desert climate that supports little wildlife, while the climate and vegetation of the San Jacinto River and Temescal Creek watershed is similar to that of the southern Central Valley. Downstream of the desert was once the coastal sage scrub and dry grassland community of the Orange County coastal plain, but that region has been almost entirely lost to urbanization. Rimming the arid portions of the watershed are the chaparral zones, consisting of sclerophyllous, thick, low bushes and small trees. The chaparral generally is found between elevations of 1,000 feet (300 m) and 6,500 feet (2,000 m), and occurs mainly closer to the coast on the windward side of the Peninsular Ranges. The scrub oak is one of the most common plants in chaparral regions, forming a dense groundcover that makes it difficult for humans and large animals such as mountain lions, coyotes, and bobcats to traverse. Chaparral growth is determined by wildfires and droughts, and depends on the semi-arid climate of the region.

Perennial and seasonal streams often are lined with live oak and sycamore, which transition into the riparian zones of the main stem Santa Ana River. The inland riparian marshes upstream of the Riverside/Orange County line, although degraded by pollution, have otherwise been mostly left in their natural state. Although much of the riparian system along the river has been degraded, one of the largest places where it occurs is the enormous marsh behind Prado Dam, an area closed to development because it functions as a flood control basin, similar to the Sepulveda Dam. The Santa Ana sucker, a small bottom-dwelling fish, once was found throughout riparian zones, but now is rarely seen in the Santa Ana River drainage. Near the mouth, the river was once abundant in salt marshes, which stretched for miles on either side of the river, even near Upper Newport Bay, which has also served as an alternate mouth of the river.

The alpine and subalpine zones, despite their high elevation (above 9500 feet, 2900 meters) and significant rainfall (up to 35 inches, 89 cm per year), are sparsely vegetated. The windswept terrain of the alpine zone is primarily small brush and weeds, while trees—mostly small gnarled pines and junipers—occur in canyons and shielded depressions in the subalpine zone. Inland elevations above 5,000 feet (1,500 m) support much denser forest. Jeffrey pine, ponderosa pine, black oak, lodgepole pine, and willow constitute most of the forested lands. The mountain habitats of the watershed support many animals typical of Californian mountain regions, including squirrels, chipmunks, black bears, mule deer, and many species of migratory birds. In the canyons of the San Bernardinos, the river is abundant in landlocked rainbow trout and is lined with alders, willow and cottonwoods. Where the river and its large upper tributaries empty out of the mountain canyons into the Inland Empire basin, they are surrounded by the alluvial scrub zone, a mix of desert and upper riparian vegetation. Along the main stem, this zone begins at the base of Seven Oaks Dam and ends at the Lytle Creek confluence.

Historically, the Santa Ana was named "the best stream in Southern California ". The steelhead is an anadromous fish, similar to salmon, that migrates up rivers and streams to spawn. Unlike salmon, which usually only reproduce once, steelhead may reproduce multiple times and have a much longer life span. Steelhead was once found along the entire main stem of the Santa Ana River, as well as on some of its main tributaries—Santiago Creek, San Antonio and Chino Creeks, Cucamonga Creek, Lytle Creek, City Creek, and Mill Creek. Few, if any, steelhead were present in Temescal Creek (although one of its tributaries was stocked in the 1930s) and none inhabited the San Jacinto River, because it is disconnected from most of the Santa Ana River system. Up to the 1950s, significant numbers of steelhead trout still migrated in from the ocean. Because of pollution and modifications to the river, very few steelhead still use the river. The exception is the presence of landlocked rainbow trout—the freshwater phase of steelhead—upstream of Seven Oaks Dam and in the upper reaches of a few tributaries. Despite the rarity of steelhead, in recent years fin samples from 13 trout were collected from Harding Canyon in the Santiago Creek tributary of the Santa Ana River and genetic analysis has shown them to be of native and not hatchery stocks.

Invasive species—those that are not native to the region—have caused problems in the watershed for many years. One of the most troublesome invasive species is the giant reed, which plagues many coastal Southern California waterways. The giant reed is similar to a tall grass or thin bamboo, but grows quickly and can take over native stands of vegetation, block the streambed, hurts the habitat of native animals, and increases the hazard of wildfires. Perhaps the largest effect that giant reed has is its usage of water. To supplement its fast growth growth rate, the giant reed population in the Santa Ana River watershed can consume 56,200 acre feet (69,300,000 m3) of water per year.

Other invasive species also have affected the Santa Ana River. One of the most prominent is the brown-headed cowbird, which feeds off parasites and insects identified with cattle, which were brought to Southern California during the Spanish Rancho period. The brown-headed cowbird is a "brood parasite", or a bird that lays its eggs in another bird's nest. One of the most afflicted birds is the Least Bell's Vireo, whose population also suffers from the loss of riparian habitat. The Least Bell's Vireo is considered an endangered species, as is the southwestern willow flycatcher, whose habitat is often shared with the other bird. The saltcedar is another invasive large weed that also, like the giant reed, uses large amounts of water. Unlike giant reed, the saltcedar has deeper roots, not only making it more difficult to remove but allowing it to access and use up deep groundwater. However, the saltcedar is similar in that it also provides little usable habitat for native animals.