Aliso: A Journal of Systematic and Evolutionary Botany Volume 5 | Issue 3 Article 8 1963 A Flora of San Clemente Island, California Peter H. Raven Follow this and additional works at: http://scholarship.claremont.edu/aliso Part of the Botany Commons Recommended Citation Raven, Peter H. (1963) "A Flora of San Clemente Island, California," Aliso: A Journal of Systematic and Evolutionary Botany: Vol. 5: Iss. 3, Article 8. Available at: http://scholarship.claremont.edu/aliso/vol5/iss3/8 ALISO VoL. 5, No.3, pp. 289-347 APRIL 15, 1963 A FLORA OF SAN CLEMENTE ISLAND, CALIFORNIA PETER H. RAVEN1 INTRODUCTION San Clemente Island is the southernmost of the Channel Islands of California, its center lying at about 32° 50' N. latitude, 118° 30' W. longitude. It is about 64 statute miles west­ northwest of San Diego and about 50 miles south-southwest of San Pedro, the nearest mainland point (Fig. 1). The nearest point of Santa Catalina Island, the closest land, is about 21 miles to the north; Catalina is thus interposed between San Clemente Island and the mainland. Santa Barbara Island lies about 40 miles northwest; San Nicolas Island about 48 miles west-northwest. Almost due south 240 miles away is Guadalupe Island, some 165 miles from the mainland of Baja California (Fig. 4). San Clemente Island is long and narrow, being nearly 21 miles long and from about 1Vz miles wide near the north end to about 4 miles wide near the south end; its long axis runs approximately northwest. For convenience, I will refer to the northeast side as the east side and the southwest side as the west side. The area of the island is about 56 square miles, and its high point, Thirst (1965 feet elevation), is near its center. The geology of San Clemente Island has been reviewed most recently by F. H. Olmsted in his "Geologic reconnaissance of San Clemente Island, California" (Geol. Surv. Bull. 1071-B: 55-68. 1958). The island is the upper part of a tilted and gently arched block of earth's crust, with a steep east slope and a more gentle west slope. Obvious, particularly on the western, relatively gentle slopes, are about 20 distinct wave-cut terraces extending up to a level of about 1500 feet, which suggests that the portion of the island below that elevation was submerged and rose intermittently, probably, as will be seen, during the Pleistocene and more recently. The island is everywhere dissected by deep, geologically young canyons, those on the east coast dropping precipitously to the sea (Fig. 2). It is in these canyons and on their rocky cliffs that many of the most interesting plants occur; probably the area about their heads has been continuously above sea level during the Pleistocene. Most of the island is composed of volcanic rocks of Miocene age, primarily andesite with a large block of dacite in the area just north of Middle Ranch and Seal Cove and smaller amounts elsewhere. Patches of rhyolite occur near the north end. Local deposits of overlying sedimentaries of various ages are scattered here and there. In the younger sand deposits (Recent) such as the dunes at West Cove and the large dune near the northwestern end, and also in deposits near China Point (Murbarger, pers. comm.), there are sand molds of tree trunks and plant roots and stems, which suggest a much moister climate on the island in the very recent past. In any event, the island is not older than the Miocene and may be younger. Geologic evidence suggests that it has never been connected with any other body of land. Most of San Clemente Island is covered with grassland dominated at present by intro­ duced Mediterranean annual herbs such as Avena barbata, A. fattta, BromtJs diandrtts, B. rttbens, Medicago polymorpha, Eroditttn cictttarium, and E. moschatum, together with such lPresent address: Division of Systematic Biology, Stanford University, Stanford, California. [289] 290 ALISO [VOL. 5, No. 3 natives. as Lyctum ~alifornicum, a low spiny ~hrub, and scattered clumps of Opuntia littoralis. Opuntta proltfera 1s abundant and forms thJCkets near the south end and is rarer northward. Mesembryc::nthemum crystallinum. and M. nodiflorum, two species of "ice plant" native to South Afnca, are also abundant m the grassland throughout, the latter species being the more frequent. Convolvulus macrostegius commonly sprawls over the slopes. Deep within SAN MIGUEL SANTA CRUZ 0 ~ ~J':, ~·· Los Angeles \../ ~ ANACAPA SANTA ROSA SANTA BARBARA SANTA CATAL~ SAN NICOLAS SAN CLEMENTE~ San Diego 25 miles Fig. 1. A portion of the coast of southern California, showing the California Channel Islands. the canyons are groves of trees, especially Prunus ilicifolia subsp. lyonii, but also Lyono­ thamnus, Quercus tomentella, Sambucus, Heteromeles, and Rhus integrifolia (Fig. 3). Long trailing plants of the snake cactus, Bergerocactus emoryi, sprawl down the rocky canyon walls. Coastal sage is very limited in area, being confined to dry canyon walls; but it seems probable that it formerly may have occupied large areas on the clayey benches, and have mostly been destroyed by animals. Although weather data are scant, the east side of the island is apparently moister than the west, and it is likely that the main tracks of the storms from north to south are often deflected down along the east side of the island. Generally the wind is from the sea, over the island and onto the mainland; but during the Santa Ana cycles of winter, violent and APRIL 15, 1963] SAN CLEME TE FLORA 291 Fig. 2. Canyon below Lemon Tank with the characteristic abrupt drop to the sea of east-s ide canyons. Oprmtia littorcdis on upper cliffs, Bergerocctctus emoryi in center, and shrubs of E1·ioph)•llum nevinii scattered below. Offic ial photograph, U.S. N avy . 292 ALISO [VoL. 5, No.3 sustained winds blow off the mainland and from Santa Catalina Island toward the east side of San Clemente. These Santa Ana winds may obviously be of importance in transporting seeds to the island. HISTORICAL CHANGES San Clemente Island was discovered by Juan Rodriguez Cabrillo on October 7, 1542. At this time it, like the other Channel Islands, supported a fairly large Indian population, which was gradually reduced to nothing in the succeeding two and a half centuries. Unfor­ tunately goats were liberated on the Channel Islands at a very early date, not later than 1827 on Santa Catalina Island (Dunkle, Allan Hancock Pac. Exped. 13: 261. 1950). By 1840 San Clemente, San Nicolas, and Santa Barbara islands were said to be densely populated with goats (Farnham, J. T., Travels in California. Oakland: Biobooks. 1947). Some trees were cut on San Clemente Island in the nineteenth century, and starting with 1877, large numbers of sheep were grazed there (Dunkle, loc. cit.). The island has been owned continuously by the United States Government, but was leased to the San Clemente Sheep and Wool Company from 1877 to about 1934, when it was transferred to the Navy and sheep grazing discontinued. As we will see, the first botanists did not reach the island until 1885, and one can only assume that the flora they observed had already been profoundly altered. By that time, it is highly likely that certain species, some of them perhaps endemics, had already become extinct. It was not until 1894 that a reasonably thorough botanical search of even the south end was carried out, and it was 1903 before the whole island was explored botanically, after at least 65 years of intensive exploitation by feral goats and 25 years of heavy use as a sheep ranch. Lyon visiting the south end in 1885, noted great dead masses of Dudleya ("Cotyledon") that formerly covered the ground throughout the entire island and had been eaten by the sheep in a season of drought, persisting only on "wholly inaccessible rocks" (Botan. Gaz. 11: 198. 1886). This suggests, as mentioned above in connection with the coastal sage, that many plants which may have once grown freely all over the island in the absence of grazing animals have survived since only on steep walls. One can only speculate, for example, about whether the endemic tree dandelion, Munzothamnus blairii, grew on the fiats formerly; but it seems certain that such components of the coasta.l sage as the endemic Castilleja grisea and the more widespread Eriophyllum confertiflorum and Artemisia californica, for example, did so. It was reported to Lyon (Botan. Gaz. 11: 204. 1886) that Lavatera assurgentiflora in about 1873 "constituted an unbroken forest, extend­ ing for miles upon the high plateaus." By 1885, and subsequently, it has been reduced to no more than a few dozen individuals, although the report of Trask (Bull. So. Calif. Acad. Sci. 3: 95. 1904) suggests that at the time of Lyon's visit there may still have been some groves on the island which Lyon did not reach. The drastic reduction of Lavatera probably parallels that of many other species that simply were not adapted to life on the cliffs (among them perhaps Dissanthelium californicum) and tends to support the above­ mentioned contention that some species may have become extinct on the island within historical times. The agressive spread of naturalized weeds, especially under the influence of severe grazing pressure on communities of plants poorly adapted to it, has doubtless also done much to decimate the native flora of the island. Among the 81 species listed by Lyon in 1885, 10 introduced ones are included. BOTANICAL EXPLORATION In April, 1885, two enthusiastic amateur botanists of Los Angeles, William Scrugham APRIL 15, 1963] SAN CLEMENTE FLORA 293 Lyon and the Rev. Joseph C. N evin, made the first collections of plants on San Clemente Island.