16 THE BBOAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



on the foothills surrounding them. Farther north, in Coast Ranges 

 and Sierras, the chaparral is more and more restricted to south-facing 

 exposures (plate 10, a, b), the opposite slopes being occupied by 

 other plants, first by broad-sclerophyll trees, and still farther by 

 conifers and broad-leaved deciduous species as well. The same 

 changes are noted in ascending the higher mountains in any part of 

 the State. 



LOCATION OF GREATEST IMPORTANCE OF THE TYPE IN THE 



CLIMAX COMMUNITY. 



This line of evidence is closely related to the last, since a plant 

 community which covers all slopes and exposures with fair uniformity 

 is likely to be the climax of that region. In another place (p. 72) 

 I will show that in certain regions the climax is dominantly of the 

 broad-sclerophyll type; that in others the broad-sclerophylls are 

 secondary and successional, and that there are intermediate areas 

 where the status of these plants is uncertain; and, finally, that the 

 region where the broad-sclerophyll type, and in particular the 

 chaparral, is most certainly climactic, is southern California. 



CONTINUITY AND CONVERGENCE OF LINES OF DISPERSAL. 



If we were to select an ideal center from which migrating species 

 might most quickly and easily reach all parts of the region where 

 broad-sclerophylls occur commonly, we would without fail fix upon 

 the vicinity of Ventura County. From this point easy migration 

 routes for all the species concerned, which would be mountain ranges 

 of moderate altitude, lead in various directions, and nowhere along 

 their courses are there barriers of any importance. From the north 

 two routes converge, the Coast Ranges, and the Sierras by way of 

 the Tehachapi Mountains. Southward are the various ranges 

 of southern and Lower California. Surely it is more than coincidence 

 that the evidence presented along other lines points to this same 

 region and the country immediately southeast of it. 



I have endeavored in this chapter to present a picture of the range 

 of the California broad-sclerophyll vegetation-type, principally by 

 superposition of the ranges of the individual species; and to show, 

 through seven lines of evidence, that the center of distribution of 

 that type is in southern California west of the deserts, from the 

 Santa Ynez and Sierra Madre Ranges southward into northern 

 Lower California. 



