110 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



pelling them to take a subordinate role. This dominance of the invaders 

 marks a new stage in the succession, which persists until its reaction upon the 

 habitat permits the invasion of new-comers of still greater demands. This 

 process continues until the climax stage is reached, when no further change 

 occurs, unless denudation again intervenes to produce a new bare area for 

 succession. 



The course of development in each succession or sere is marked by a series 

 of stages or communities of progressively higher requirements, determined 

 largely by the characteristic vegetation-form. While they differ in nature and 

 composition, they are alike in being more or less temporary as well as in playing 

 an intrinsic part in the development of the climax. As a consequence, they 

 are termed developmental, successional, or serai communities, in contrast 

 with the final and permanent cUmax communities. Apart from this basic 

 distinction, a serai community exhibits much the same structure as a climax 

 one. Both are associations of two or more dominants, and exhibit societies 

 of subdominants. Practically as well as developmentally, however, the dis- 

 tinction between temporary and serai communities and permanent climax 

 ones is so important that it has proved desirable to use terms which at once 

 place each in its proper developmental position. Accordingly, each serai 

 stage or conmiunity is termed an associes i. e., it is a temporary or develop- 

 mental association. Similarly, the community formed by each dominant is 

 called a consocies and that by each subdominant a socies, corresponding 

 respectively to consociation and society. In addition, the terms family and 

 colony are used for initial stages in which dominance is lacking or little 

 developed. The colony is the community formed by two or more pioneer 

 species, while the family consists of individuals belonging to a single species. 

 The colony is regularly characteristic of the initial stages of succession. 



An associes consists, like an association, of two or more dominants or con- 

 socies. The most familiar example is the reed-swamp, which usually com- 

 prises three consocies, Scirpits Uiaustris, Typha latifolia or T. angustifolia, 

 and Phragmites communis. In extensive swamps, all of these occur, usually 

 alternating or sometimes mixed, and in northern regions with a fourth con- 

 socies, Zizania aquatica. Over much of the West, Scirpus and Typha alone 

 are found together and in many localized areas only one or the other is present. 

 Some socies, such as Heleocharis, Sagittaria, and Alismxi, are practically 

 coextensive with the dominants, though not always to be found in each local 

 area. Other subdominants are more restricted, and some are more frequently 

 associated with one consocies than with the other. Other well-marked 

 associes are Nymphaea-Potamogeton in ponds, Ammophila-Elymus on sand- 

 dunes, Redfiddia-Muhlenbergia in blow-outs, Spirostachys-Dondia in salt 

 marshes, Popidus-Betula in bums, and Gutierrezia-Artemisia frigida in dis- 

 turbed areas. 



The designation of serai communities is essentially like that of climax 

 ones. The associes is distinguished by the use of its two most important 

 consocies, as the Scirpus-Typha associes or reed-swamp, while consocies and 

 socies are named from the dominant or subdominant, as the Scirpus con- 

 socies, Nymphaea consocies, Popvlus tremuloides consocies, Sagittaria socies, 

 PerUstemon socies, etc. Colonies are like associes in requiring the names of 

 the two most important species for designation. 



