180 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



The successional relations of the chaparral are expressed chiefly in the 

 xerosere and the subsere. The primary succession is found usually on rock 

 outcrops and especially on talus slides, and exhibits the same essential stages 

 in the various regions. The subsere is much the most frequent and important, 

 especially from the practical side. It is regularly caused by fire, and it is 

 probable that all chaparral areas, as they exist to-day, have resulted from fire. 

 This does not mean, however, that all chaparral was originally developed in 

 response to fire. Like grassland, it originated in response to a xeroid climate 

 and followed the latter in its extension into new regions. Like grassland, 

 also, it was able to develop its natural dominance after fire much more quickly 

 than forest could, with the result that fire has constantly increased the area 

 of chaparral at the expense of the forest. As a consequence, chaparral con- 

 sists of two distinct types developmentally. The original and most typical is 

 climax chaparral, corresponding to a climate whose water efficiency is lower 

 than that demanded by forest. The most recent type is subclimax chaparral, 

 which occupies a zone of variable width about the climax proper. It is not 

 only the result of the destruction of the original forest by fire, or clearing and 

 fire, but also owes its persistence to the periodic recurrence of these disturbing 

 processes. While it is necessary to trace the process of succession in each 

 region to determine the nature of the chaparral with complete certainty, the 

 indicators left by the denuding agent as well as the development itself are 

 usually sufficient to permit a trustworthy decision. The distinction between 

 climax and subclimax chaparral is of the first importance in the treatment of 

 a region, and this matter is further discussed on a later page. 



Range and extent. — Chaparral does not dominate great areas, as is the case 

 with grassland and sagebrush. While it occurs in considerable bodies under 

 the most favorable conditions, it is generally found in relatively narrow and 

 often much interrupted belts along the edge of forest formations. Conse- 

 quently, while the formation has an exceedingly wide range, it posesses rela- 

 tively little continuity, and hence is little impressive over much of its broad 

 extent. It is poorly developed along the line of contact between the deciduous 

 forest and grassland, attains fair expression along the base of the main range 

 of the Rocky Mountains, becomes massive in the Wasatch Mountains of Utah, 

 and reaches its fullest expression in California. 



As a climax, the chaparral is found from Wyoming and the Black Hills of 

 South Dakota southward along the Rockies into Texas and Mexico. It 

 extends across Utah, New Mexico, and Arizona along the mountain ranges. 

 It is greatly broken up by the mass of the sagebrush and desert scrub forma- 

 tions in Nevada and in the Mohave and Colorado Deserts, but it reappears on 

 the mountain ranges of southern California and the Sierra Nevada. Chaparral 

 is to-day perhaps the most characteristic association found in California, but 

 it rapidly loses its importance with increasing rainfall and the consequent 

 development of forest. In northern California and in Oregon it becomes 

 limited to the drier slopes more and more and finally becomes a mere subclimax 

 or completely disappears. 



The chaparral dominants belong to 30 genera, the majority of which range 

 throughout the formation. This is particularly true of Quercus, Cercocarpus, 

 Ceanothus, Rhus, Prunus, Amelanchier, Symphoricarpus, Rosa, Opulaster, 

 Purshia, Ribes, and Cornus. A striking group of genera is limited to the 

 Southwest or finds its chief development there. This consists of Peraphyllum, 



