76 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



The direct evidence for the cUmax nature of the chaparral is 

 derived from a study of the successions themselves, in which we 

 find that all that have been investigated in a rather widely extended 

 exploration culminate in the establishment of this community, and 

 that over much of the region there is no evidence that any other 

 community is superseding it. Detailed consideration of the succes- 

 sions is reserved for a separate section. 



EXTENT OF THE CHAPARRAL AS A TRUE CLIMAX. 



Because of widespread disturbance by various agents of destruc- 

 tion, it is impossible to set definite and certain limits to the region 

 of true chaparral dominance. Fire occurring in the transition zone 

 between two formations seriously alters the normal relations due to 

 climatic control. Another source of difficulty lies in the fact that 

 much of the original vegetation of the economically more useful land 

 has been totally destroyed by the invading white man, so that it is 

 necessary to reconstruct the original picture from fragments. Certain 

 areas, however, may be fixed upon as chaparral climax which will 

 not be questioned. 



The foothills and low mountains of southern California and certain 

 parts of the valleys and mesas are the most certain, and it is probable 

 that exploration of northern Lower California would add a large 

 extent of country to the range of the chaparral climax. In these 

 places Adenostoma is usually the dominant species, or if cultivation 

 has largely destroyed the native vegetation, remnants show it to 

 have been so at a former time. Such is the case in portions of the 

 Los Angeles and San Bernardino Valleys and on the broad mesas 

 east of San Diego. As we ascend the higher mountain ranges of 

 southern California, the evidences of climactic character in the 

 chaparral become less and less convincing. Species which belong 

 to the conifer-forest chaparral appear, and there is more and more 

 alternation with patchy areas of broad-sclerophyll and of conifer 

 forest, in which Pseudotsuga macrocarpa is the first to attain impor- 

 tance. In this region there has plainly been an increase of the chapar- 

 ral areas at the expense of the forest, due to the fact that repeated 

 fires in a transition zone favor the extension of the more xerophytic 

 community. Passing northward in the Coast Ranges, we encounter 

 a simiilar transition, except that there is practically no admixture 

 of conifer-forest chaparral species until we are well north of San 

 Francisco Bay, and that the alternation is with broad-sclerophyll 

 tree species alone. Here, too, the forest areas show frequent evidence 

 of fire restriction. In the southern Sierras there is a belt along the 

 lower foothills where Adenostoma and other chaparral species are 

 of great importance, alternating, however, with much broad-sclero- 

 phyll forest. As we go northward, the yellow pine zone, with its 

 accompanying temporary chaparral, approaches more and more 



