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Parks and pools: a southern California reserve protects vanishing habitats

Natural History, April, 2002 by Robert H. Mohlenbrock

Southeast of Los Angeles, the Santa Ana Mountains extend northwest to southeast for approximately forty miles. Though the Santa Anas' highest point is 5,687-foot Santiago Peak, the elevation along the crest of this narrow range averages about 3,800 feet. At its southern end, the terrain drops down to the Santa Rosa Plateau, a 2,000-foot-high tableland with canyons, mesas, and low hills. Much of the land is capped by basalt from ancient lava flows, but outcroppings of granite and shale appear throughout the plateau.

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One attraction of the area is its animal life. Most likely to be seen are red-tailed hawks, American kestrels, Aleutian Canada geese, and golden eagles. Bobcats, foxes, and mountain lions are present but more secretive. The coastal rosy boa, a gray snake with brown longitudinal stripes, occasionally shows itself. Rare species include the Pacific pond turtle, the California red-legged frog, the California newt, and the California tree frog.

The jewels of the plateau are two habitats--Engelmann oak woodland and vernal (springtime) pools--that are now quite rare elsewhere in southern California as a result of suburban development. Fortunately, more than half of the twenty-three-square-mile plateau is protected as the Santa Rosa Plateau Ecological Reserve. This reserve, for which land was acquired beginning in 1984, is a cooperative management project of the Nature Conservancy, the Riverside County Regional Park and Open-Space District, the California Department of Fish and Game, the U.S. Fish and Wildlife Service, and the Metropolitan Water District of Southern California.

The Engelmann oak woodland, located near the base of the hills, has a parklike appearance. Enough moisture is available below ground to support the canopy of trees, but the habitat is generally so dry that the undergrowth consists largely of grass.

Thirteen vernal pools, ranging in size from a quarter acre to nearly twenty-five acres, develop mostly on the tops of mesas. They fill with water during winter storms, and since the hardpan beneath them prevents drainage, they dry up only through evaporation. As the pools gradually shrink during the warm days of spring and early summer, successive waves of annual wildflowers bloom along their margins. By late July or early August, these die out, and all that is left of the vernal pools are cracked, dry depressions.

HABITATS

Engelmann oak woodland. Engelmann oaks, with their oblong, wavy-edged leaves, are joined by coastal live oaks, with elliptical, smooth-edged leaves. Deergrass is the main species in the understory. Shrubs: holly-leaf cherry, sugar bush, laurel sumac, white-flowered currant, Acourtia microcephala. Wildflowers: Parry's larkspur, flax-leaved linanthus, lace pod, two lavender-flowered species of Phacelia.

Vernal pools. In spring, the wetter margins are dominated by Downingia bella and D. cuspidata, two blue-flowered species in the same family as bellflowers. In drier, outer zones grow rings of Blennospermum nana and goldfields; both are members of the aster family, with daisylike yellow fiower heads. Two diminutive plants--pillwort, a grasslike fern that grows in the drier zones, and waterwort, a plant with spatula-shaped leaves that is found in some of the vernal pools--are species that live in this California habitat as well as in Chile, but not in between. In the vernal pools, along with the waterwort, grows San Diego button celery, a dwarf member of the carrot family.

Grassland. Deergrass, purple needlegrass, and Malpais bluegrass are the principal species. Wildflowers: grape soda lupine, lilac Mariposa lily, checker mallow, California blue-eyed grass (not actually a grass but a plant in the iris family).

Chaparral. The slopes of some hills and mesas support a community of shrubs and wildflowers; the only tree of significance is scrub oak. At the higher elevations, manzanita is the abundant shrub, while midslope shrubs include chamise, coffeeberry, redberry, and two kinds of mountain mahoganies. Near the bottom, California buckwheat and California sagebrush dominate. Wildflowers: various penstemons and lupines.

Streamside and aquatic habitats. Watercourses flow seasonally through the major canyons. Within the streams are deep pools, called tenajas, that persist throughout most years. Sedges, rushes, and cattails border the streams. Whitewater crowfoot and the tiny aquatic mosquito fern grow in the water, while monkeyssflower is common nearby. Trees: western sycamore, red willow, Fremont's cottonwood.

For visitor information, contact: Santa Rosa Plateau Ecological Reserve 39400 Clinton Keith Road Murrieta, CA 92562 (909) 677-6951

www.santarosaplateau.org

Robert H. Mohlenbrock, professor emeritus of plant biology at Southern Illinois University, Carbondale, explores the biological and geological highlights of U.S. national forests and other parklands.

Parks and pools: a southern California reserve protects vanishing habitats

Natural History, April, 2002 by Robert H. Mohlenbrock

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