Natural History: Channeling in California

Native vegetation is rebounding on Santa Catalina Island.

A dense fog hung over the Gulf of Santa Catalina as my wife, Beverly, and I boarded a high-speed boat at Dana Point, not far from the famous Mission San Juan Capistrano, southeast of Los Angeles. It took just an hour and a half to cross the thirty-five miles that separated the mainland from our destination, Santa Catalina Island. Covering seventy-six square miles, Santa Catalina is one of southern California's eight Channel Islands. Five others--San Miguel, Santa Rosa, Santa Cruz, Anacapa, and Santa Barbara--constitute Channel Islands National Park. The remaining two are San Nicolas and San Clemente.

The Channel Islands (often called the Santa Barbara Islands) began emerging above sea level about 5 million years ago as volcanic, igneous, sedimentary, and metamorphic rocks were uplifted by tectonic forces associated with the San Andreas Fault. Some, including Santa Catalina, were also overlain by lava flows. During the last glaciation, when sea levels were roughly 400 feet lower, a few of the islands were connected to each other, but all of them have always been isolated from the mainland. As a result, each hosts a variety of endemic plants and animals--that is, species or subspecies found only there.

Santa Catalina is twenty-two miles long and ranges in width from half a mile, at an isthmus, to eight miles. It is essentially a mountain ridge, the highest point being 2,097-foot Mount Orizaba. Along the coast, precipitous cliffs up to 1,400 feet high are interspersed with coves and bays leading into deep, V-shaped canyons. Most of the beaches in the coves are covered with cobblestones, while a few are sandy. Summers are warm and dry: most of the annual rainfall of twelve or more inches falls during the winter. Although the Santa Ana winds that blow from the mainland in winter are often violent, temperatures remain mild.

The original vegetation of Santa Catalina Island has been altered by human activity, particularly through the introduction, more than a century ago, of sheep, goats, and cattle, followed by mule deer, wild pigs, and bison. After years of intense grazing, existing chaparral and coastal scrub communities were largely replaced by nonnative grasses. During the last half of the twentieth century, however, efforts were made to control feral goats and pigs and to remove some of the cattle and bison (only a small herd of bison now remains as a tourist attraction). Today, 88 percent of the island is owned by the Santa Catalina Island Conservancy, which was formed in 1972, and the original vegetation is gradually being renewed.

The habitats include oak woodland, riparian woodland, chaparral, coastal scrub, bluff faces, maritime desert scrub, grasslands, and marshy areas and ponds. About 640 plant species have been recorded on Santa Catalina, nearly two-thirds of them native. Most of the native plants can also be found in the Santa Monica Mountains on the mainland, but several are restricted to the Channel Islands or just to Santa Catalina. Some of the rarest plants live on steep rocky cliffs that have been inaccessible to the island's feral goats.

A California quail and a Bewick's wren are among four bird subspecies found only on Santa Catalina. Native mammals include five endemic subspecies, the largest of which is a Channel Island fox. There are also various endemic invertebrates, including two snails, several butterflies and moths, a few beetles, a cricket, and a walking stick.

HABITATS

Oak woodland develops best in moist, protected canyons and valleys with deep alluvial soils. Island oak, canyon oak, and scrub oak are common, along with Catalina cherry, elderberry, and summer holly (actually a member of the heath family). The rare Catalina ironwood is found in Toyon Canyon and in a few other canyons. Wildflowers include miner's lettuce, lacepod, a buttercup, and the showy fiesta flower (a member of the same family as waterleaf). Among the ferns are California polypody, maidenhair fern, and golden-back fern.

Riparian woodland, with black cottonwood and Fremont cottonwood as the major trees, grows along the streams of canyon floors. Red willow, arroyo willow, elderberry, and McDonald oak are present in the tree and shrub layers. Low-growing shrubs include wild rose, California blackberry, and snowberry. Wild honeysuckle, wild grape, redroot (a type of wild cucumber), and coral vine climb over the vegetation. Purple vervain is one of the few colorful wildflowers.

Chaparral is found on north- and east-facing slopes on the side of the island facing the mainland and also in arroyos (dry gullies that carry water after a rain) on the Pacific slopes. One of the best of these sparsely vegetated, shrubby habitats is found on the western slopes of BlackJack Mountain. Among the shrubby species are a tree poppy, three kinds of sumacs (lemonade, laurel sumac, and sugar sumac), chamise, island buckthorn, mountain mahogany, Christmas berry (toyon), pitcher sage, wild apple (which is not an apple, despite the similar appearance of the fruit), and Santa Catalina and white lilacs (not really lilacs but relatives of the New Jersey tea of the eastern United States). An uncommon endemic on the slopes of Black Jack Mountain is Greene's rockrose. Of the few wildflowers, figwort and everlasting appear to be the most common.

Coastal scrub appears on some of the canyon slopes where the soil is extremely thin and rocky. A good place to observe this open habitat is above the beach at Little Harbor, on the island's west side. California sagebrush dominates, although prickly pear, lemonade, laurel sumac, deerbrush, white sage, and black sage are common. St.-Catherine's-lace has huge clusters of white flowers on a stem that may reach twelve feet tall. A species of tree mallow attains a similar height.

Bluff face plants include the fleshy-stemmed sea dahlia; alabaster plant, a species with fleshy leaves; dusty-miller, with its gray leaves and stems; bush snapdragon; sticky monkey-flower; and snake's-head, a tall perennial in the aster family. Two species of live-forever (a succulent) grow from crevices in the steep cliffs.

Maritime desert scrub is the most arid of the island's habitats. It occurs on headlands, such as the southwestern side of Indian Head Point, that are exposed to prevailing westerly winds blowing in from the Pacific. Velvet cactus, prickly pear, Bergerocactus emoryi, and cholla are widespread, often joined by box thorn, a prickly shrub in the nightshade family. Other common plants are brittlebush, California sagebrush, several wildflowers in the aster family, and a wild four-o'clock.

Grassland areas have begun to see the return of some native species, including feather love grass and two kinds of needlegrass. In early spring, the grasslands are often covered with the shiny yellow heads of goldfields. Other wildflowers interspersed among the grasses are tidy tips, red maids, Indian paintbrush, owl's clover, shooting-star, larkspur, golden star, mariposa lily, and johnny-jump-up.

Freshwater marsh and aquatic plants can be seen throughout the year in Cottonwood Canyon and Bulrush Canyon. Among them are scouring rushes, brass-buttons, yerba mama, watercress, camphorweed, two kinds of cattails, and a variety of sedges and rushes.

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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.