THE CHAPARRAL CLIMAX. 177 



annually recurrent drought of late spring and early summer. Hence, they are 

 strictly pioneer socies and families, but by virtue of their annual recurrence 

 they may well be treated as societies of annuals. In addition to these, there 

 are the herbaceous communities of dunes, washes, and salt-spots, and of dis- 

 turbed areas, which are successional in nature. A large number of these serai 

 annuals are identical with those already mentioned. Finally, there are a num- 

 ber of perennial grasses, some of which have entered from the desert plains in 

 contact with the scrub at its upper limit, and others which may be regarded 

 as relicts of a former savannah condition of certain portions of the desert 

 scrub. Such are Muhlenbergia porteri, Aristida divaricata, and Bouteloua 

 rothrockii in particular. The lists given above are contributed by Professor 

 J. J. Thornber and are based chiefly upon studies in southern Arizona, though 

 the majority of species extend throughout the association. 



THE CHAPARRAL CLIMAX. 

 QUERCUS-CEANOTHUS FORMATION. 



Nature. — The chaparral formation is characterized by low shrubs of the 

 same vegetation-form and for the most part of similar systematic relationship. 

 In comparison with forest, it is xeroid in character, but distinctly less so than 

 sagebrush and desert scrub, which resemble it in physiognomy. It is not 

 dwarfed woodland, similar to that found at timber-line. It not only lacks 

 the habit of "elfin" wood, but the characteristic species, with the exception 

 of those of Quercus, do not belong to tree genera. In fact, there is little more 

 reason for regarding chaparral as dwarfed forest than for treating sagebrush 

 or Larrea desert as such. It represents a distinct ecological type, intermediate 

 in character and requirements between grassland or scrub desert, i. e., sage- 

 brush and mesquite on the one hand and forest or woodland on the other. 

 This is supported by its almost universal occurrence in front of forest or 

 around it wherever it meets grassland or desert. While timber-line scrub has 

 a general resemblance to chaparral at the first glance, it differs essentially in 

 habitat, floristic, and physiognomy, and belongs to a wholly different category. 



The term chaparral is in general use throughout the West and Southwest 

 for scrub or thicket. It is most commonly applied to the mesquite of Texas 

 and the Adenostoma-Ceanothus association of California, and less frequently 

 to the Quercus-Cercocarpus community of the Rocky Mountains region. In 

 spite of their general resemblance to chaparral, this term seems never to be 

 used for sagebrush or for the creosote-bush desert (Larrea consociation). 

 Naturally, it is in common use in those regions where Spanish influences are 

 still felt, and it disappears gradually to the northward long before the com- 

 munity itself has disappeared. In restricting the word to one formation and 

 in broadening it to cover all the associations of that climax, the thought has 

 been to follow the major usage and at the same time to definitize it. As a 

 result, all the associations of this formation from the Missouri Valley to the 

 Pacific Coast are designated as chaparral on account of the essential eco- 

 logical unity discussed below. A further refinement has been made in dis- 

 tinguishing climax and subclimax chaparral, both in the East and West. As 

 indicated later, these are so closely related successionally and have so many 

 points in common that a distinct term for the subclimax chaparral seems both 

 unnecessary and unwise. 



