82 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



and over much of the Coast Range" was originally grassland of the 

 bunch-grass type, Stipa being the most important genus, which has 

 been almost entirely replaced by the introduced annual grasses 

 (Avena fatua and A. barbata) that are so prominent to-day. He 

 admits the unlikeness of the climate, especially in seasonal distribu- 

 tion of precipitation, to that of other regions of grassland climax, 

 but rightly affirms that the climax plant community is itself the 

 best available indicator of climate. The decision rests, therefore, 

 upon correct identification of the climax community. Clements's 

 evidence of grassland dominance is based upon assumed relicts, 

 and my evidence of chaparral dominance is of the same nature. 

 In an area where individuals and patches of both types occur today, 

 the weight of probability would, in my opinion, favor the chaparral 

 plants as being the survivors of the true regional climax. It has 

 already been stated that most of the species of the climax chaparral, 

 notably Adenostoma, reestablish themselves with the utmost difficulty 

 once their mass control has been destroyed, and that therefore thor- 

 oughly isolated individuals or patches of such plants are almost 

 certainly relicts of former dominance rather than centers of recent 

 colonization. The same is not true in the case of grasses, even the 

 perennial species which make the grassland climaxes. With these, 

 greater mobility and ease of germination bring about a wide scattering 

 of individuals, and the acceptance of isolated plants or patches as 

 true relicts is therefore rather hazardous. 



The acceptance of my conclusions as to former control of certain 

 regions (the main mass of the Coast Ranges with its minor valleys, 

 the foothills of the southern Sierras, and perhaps the northern end 

 of the Sacramento Valley) by chaparral does not necessarily preclude 

 the possibility of climatic grassland over much of the Great Valley. 



In southern California the contact between chaparral and coastal 

 sagebrush resembles that between the former and the grassland in 

 the central part of the state. The sagebrush, which is undoubtedly 

 climax in certain portions of the interior valleys, has extended its 

 area of dominance at the expense of the chaparral, because of fire. 



In conclusion, then, the climax chaparral has transgressed its 

 normal climatic limits along its mesophytic border through its 

 invasion of the forest, fire being the causative agent; on its xerophytic 

 border it has been pushed back a considerable distance by the grasses 

 and xerophytic forest in the north, and by the coastal sagebrush 

 in the south. 



SUCCESSIONS LEADING TO THE CHAPARRAL CLIMAX. 



Primary Successions. 



The areas where primary succession may be observed are limited, 

 the bulk of the area having reached its final stage or being in process 

 of secondary development. Naturally most of the successions are 



