NO. 3 DUNKLE : PLANT ECOLOGY, CHANNEL ISLANDS 287 



which occur at an approximate elevation of 61 meters (200 feet). Small 

 groves of Lyonothamnus occur also on Santa Rosa, Santa Catalina, and 

 San Clemente. These groves are all on the northern or northeastern 

 slopes. The groves on Santa Cruz are the most extensive and consist of 

 larger trees (plate 4a). 



Quercus tomentella occurs as isolated trees about the head of eastern 

 canyons on San Clemente. In Gallagher's Canyon on Santa Catalina 

 there is an extensive grove which has a decided forest aspect. On Santa 

 Rosa, Santa Cruz, and Anacapa islands this endemic oak occurs in 

 small, dense groves about the heads of northern canyons. The one 

 grove on Anacapa is shown in plate 4b. The smaller clumps of trees 

 farther down the canyon are Photinia arbutifolia and Prunus Lyonii. 



Scattered trees of Quercus MacDonaldii occur in broad, upland 

 canyons of Santa Catalina. Q. agrifolia grows on Santa Rosa and Santa 

 Cruz, both in canyons and on protected slopes. A few trees of Q. chrys- 

 olepis and Photinia arbutifolia macrocarpa are to be found in pro- 

 tected canyon heads on San Clemente, while Prunus Lyonii is in some 

 of the western gorges of this island in the form of trees up to 15 meters 

 (49 feet). Photinia^ Prunus, Cercocarpus betuloides and its varities, 

 and Sambucus coerulea occur, usually as scattered trees, in the canyons 

 of Santa Catalina. 



On Santa Catalina a rather open riparian association varies from 

 canyon to canyon, according to altitude, soil and available water supply. 

 Among the trees and arborescent shrubs are Populus trichocarpa, P. 

 Fremontii, Salix lasiolepis, S. Laevigata, Quercus tomentella, Q. Mac- 

 Donaldii, Photinia, Sambucus, Prunus, and Cerocarpus. In Cherry 

 Valley there is an extensive, almost pure stand of Prunus which forms 

 a most picturesque, miniature woodland. The riparian woodlands of 

 Santa Cruz and Santa Rosa consist mainly of the same species as on 

 Santa Catalina with the addition of Q. agrifolia. It is highly significant 

 that several of the mainland riparian and near-riparian genera are 

 entirely lacking on the islands, for examples, Platanus, Alnus, Myrica, 

 and Umbellularia, 



In forested areas on the islands there is very little undergrowth, due 

 principally to two factors : ( 1 ) the utilization of all the available water 

 by the trees because the precipitation is usually below the amount 

 ordinarily required for tree growth, and (2) the intolerance of most of 

 the island plants to shade, especially to the deep shade of the dense 

 foliage of the everygreen sclerophylls. Woodland can be considered as 

 climax only in limited areas where local edaphic conditions favor the 

 retention of soil water, or where underground drainage carries water 



