20 THE BBOAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



III. THE COMMUNITIES. 



The terminology of plant communities is just now in a state 

 of flux, and therefore it is too much to hope that the system employed 

 in this paper will be satisfactory to every reader. The best that 

 the author can do is to define his terms accurately and relate them 

 clearly to the uses of other writers. It is therefore necessary to 

 submit the following definitions: 



The Formation. The fundamental unit of vegetation : a community 

 relatively homogeneous ecologically in the character of its dominants, 

 fioristically in that its locally varying subdivisions are bound together 

 by the common dominance of one or more species or by the equiva- 

 lence of species ecologically near of kin, and developmentally in that 

 within a given climatic region it has a constant successional role. 



The Association. A vegetation unit of lower rank than the 

 formation and contained within it; differing from other associations 

 within the same formation with respect to any or all of the bases of 

 the formation (ecological character, floristics, development), in 

 minor degree, but sufficiently to cause it to stand out as a distinct 

 entity. 



These two units are analogous, respectively, to the taxonomic 

 units, species, and variety, and one may conveniently refer to the 

 range of a formation or association exactly as one speaks of that of a 

 species or variety. In naming the formations I would use descriptive 

 titles based upon ecological character, and for the associations I 

 would employ, when possible, the names of dominants. 



The Consociation, an association with a single dominant, is fre- 

 quently a useful term. The word "community" is an indispensable 

 addition to the list, being used to designate any vegetation unit 

 without specifying its rank. 



These terms must now be related to two recent systems, that of 

 Clements (21) and that of Nichols (69). Clements applies the 

 term formation to the climax community only ; I would extend it to 

 successional communities as well. Clements distinguishes between 

 the climax units association and consociation and the successional 

 associes and consocies; my use of association and consociation includes 

 both types of communities. The formation of the present paper 

 agrees in substance with the association-type of Nichols; in the use 

 of the terms association and consociation we are in essential agreement. 



THE BROAD-SCLEROPHYLL COMMUNITIES. 



There are two Californian formations in which the broad-sclero- 

 phylls are the dominating element — the broad-sclerophyll forest 

 formation and the chaparral formation. Each is in part climax, 

 in part successional. Further, there is a broad-sclerophyll element 

 of minor importance in the redwood forest, making a rather large 



