THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 29 



number of consociations and mixtures might be distinguished. 

 In the higher northern Sierras half a dozen species are of paramount 

 importance. These are Castanopsis sempervirens, Quercus vac- 

 cinifolia, Prunus emarginata, Ceanothus cordulatus, C. velutinus, 

 Arctostaphylos nevadensis, and A. patula. They occur in all possible 

 combinations, so that a classification for one region may not fit 

 another at all. We should also mention the thickets of deciduous 

 oaks, especially Quercus kelloggii and Q. garryana, which are so 

 extensive in the mountains of Trinity County and northward. 

 These species, ordinarily trees, here grow in dense masses like the 

 chaparral, forming a connecting link ecologically with the deciduous 

 oak thickets of the Rocky Mountain foothills. 



The following outline of the broad-sclerophyll communities will 

 serve as summary to this chapter, all being climax except those 

 specially noted: 



A. Broad-sclerophyll forest formation. 



1. Pasania-Quercus-Arbutus association. 



2. Quercus agrifolia-Arbutus association. 



2a. Quercus agrifolia consociation. 

 26. Umbellularia consociation. 



3. Quercus agrifolia-lobata association. 



4. Quercus chrysolepis-kelloggii association. 



4a. Quercus chrysolepis consociation (successional) . 



B. Chaparral formation. 



1. Climax chaparral association. 



la. Adenostoma and other consociat'ons and various mixtures. 



2. Conifer forest chaparral association (successional). 



2a. Numerous vague minor units. 



