THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 23 



californica, Acer macrophyllum, and Pseudotsuga, making a rather 

 typical specimen of the Pasania-Quercus-Arbutus association. The 

 first redwoods appear in groups of large trees on the valley bottom, 

 with scattered individuals on north slopes (plate 8a). This con- 

 tinues for 15 kilometers or more, then for several kilometers there is an 

 almost pure forest of Sequoia on north slopes with the Pasania- 

 Quercus-Arbutus association on south exposures. Finally the forest 

 becomes nearly pure Sequoia on all slopes, the broad-sclerophylls 

 gradually disappearing as a distinct community, though remaining 

 to some extent as a layer society, particularly Arbutus and Pasania. 



Quercus agrifolia- Arbutus Association. — This unit is coastal, occur- 

 ring from the northern limit of Quercus agrifolia in Mendocino County 

 to the southern limit of Arbutus in Los Angeles County. It is thus 

 characteristic of the outer central Coast Ranges, where it is the 

 dominant cover on north-facing slopes. It is particularly well 

 developed in the San Francisco Bay region and southward to the 

 Santa Lucia Mountains. The character tree is Quercus agrifolia.^ 

 Arbutus menziesii is next in importance, but varies greatly in 

 abundance in different localities. Msculus californica, a deciduous 

 species, is usually prominent, and Umbellularia californica is equally 

 so. Acer macrophyllum is frequently important in the more meso- 

 phytic localities. In areas that are transitional with the Sequoia 

 association, Pasania, Quercus chrysolepis, Q. kelloggii, and Sequoia 

 itself occur. Since a typical area of this association is described in 

 another part of this paper (p. 38), it will be unnecessary to go further 

 into details here. Station 7 at Jasper Ridge is representative in 

 every respect (plates 14a, 8b). 



Quercus agrifolia Consociation. — South of the southern limit of 

 Arbutus (Los Angeles County) the community is continued as a 

 consociation dominated by Quercus agrifolia. This is rather promi- 

 nent in the lower altitudes of the west slope of the Cuyamaca Moun- 

 tains. 



Umbellularia Consociation. — Umbellularia occurs scattered through 

 the Quercus agrifolia-Arbutus association, and in others as well, but 

 it also forms pure growths, especially in the central Coast Ranges, 

 occupying moist ravines and canyon bottoms. These groups of 

 Umbellularia stand out strikingly above the other trees, being con- 

 spicuous by reason of their light green color and conifer-like form. 

 The shade is very dense and undergrowth almost lacking. Umbel- 

 lularia itself, however, is able to germinate successfully under such 

 conditions. 



Quercus agrifolia-lobata Association (plate 9a). — This is charac- 

 teristic of the broad valleys and gentle footslopes of the central 



' In some places, especially in the inner Coast Ranges, it is replaced by Q. wislizeni, and thus 

 another association might be distinguished. 



