14 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



In Southern California 47 species occur, and the following 13 

 are confined to the region or extend into Lower California: 



Quercus engelmanni. Ceanothus crassifolius. Ceanothus oliganthus. 



Adenostoma sparsifolium. megacarpus. Comarostaphylis diversifolia. 



Rhus integrifolia. spinosus. Xylococcus bicolor. 



laurina. verrucosus. Arctostaphylos drupacea. 



ovata. 



Summarizing from the map and the lists just given, we see first 

 that California and Lower California are the home of the broad- 

 sclerophylls. The number of species diminishes eastward very 

 rapidly, and northward along the coast more gradually. Further, 

 we see that the greatest number of species occur in the Coast Ranges 

 and Southern California. By a division into four areas we discover 

 that the Sierras are poorest both in total number of species and in 

 endemics; that the north and south Coast Ranges are next, being 

 about equal in total numbers, but very unequal in endemics, the 

 north portion having one and the south six; and that southern 

 California stands highest with respect to both categories. Our 

 evidence therefore points to southern California as the center of 

 distribution of the broad-sclerophylls, and confirmation of this 

 conclusion will be found in the paragraphs following. 



LOCATION OF DOMINANCE OR GREAT ABUNDANCE OF 



INDIVIDUALS. 



It is a matter of easy observation that the chaparral fields have 

 their greatest extent and dominance in southern California. We 

 have only to cite as examples the mountains of Ventura County 

 (plate lie), the lower ridges of the San Gabriel, the San Bernardino 

 and San Jacinto Ranges, and the Cuyamaca Mountains (plate 11a). 

 Without doubt the same is true of northern Lower California. 

 Traveling northward, we find in both Coast Ranges and Sierras 

 a gradual decrease in the vegetational importance of the broad- 

 sclerophylls. The chaparral areas are more and more restricted, 

 and increasingly dominated by species of successional status. In 

 the southern Coast Ranges and Sierras the change is not so notable, 

 but it intensifies as we reach the central portion of the State. A 

 similar decrease is seen, very naturally, as we ascend to higher alti- 

 tudes in all parts of the region. In the northern portion of the 

 State and beyond its limits, the broad-sclerophylls lose their domi- 

 nance altogether and become less and less important vegetationally. 

 Eastward the decrease is very sharp, so that beyond the western 

 borders of the deserts and the middle forest region of the Sierras 

 the type is almost altogether absent as a vegetational entity. 



LOCATION OF SYNTHETIC OR CLOSELY RELATED FORMS. 

 It is impossible, in the present state of our knowledge, to obtain 

 accurate data upon this point. However, the very confusion which 



