Il] MAIN HABITATS, SUCCESSIONS, AND CLIMAXES 329 



evident that, at least in the present state of the world, different areas 

 in the same climatic belt can support widely different climaxes. 



Main Climaxes 



Although competition is the chief key to succession, the final out- 

 come of this latter lies in the population besi fitted (among those 

 naturally attainable locally) to take advantage of the relatively mesic 

 conditions brought about by past reactions. This population is the 

 ' climax ' (often more cautiously termed ' climax type ', and compare 

 the reservation on page 323) and, being in close harmony with an 

 essentially stable environment, is more or less permanent. Though 

 by no means invariable in time and space, it shows a regularity of 

 physiognomy and floristic composition that is usually lacking in 

 successional stages. Thus in over-all form it persists as long as the 

 climate remains unchanged — provided no new dominant enters or 

 retrogressive change sets in, e.g. through impoverishment of the soil 

 or accumulation of toxic substances. Dominance is due primarily 

 to control of some ' key ' factor or factors of the environment, the 

 dominant or co-dominants making of all plants present the greatest 

 demands on the habitat, and normally when the climax is reached 

 excluding invasion by any serious rival. Fluctuations in the com- 

 munity thereafter tend to be minor in the absence of any forceful 

 change. 



The climax is thus an equilibrated state of community compo- 

 sition and productivity, that is adapted to maximum utilization of 

 local resources by plants and, normally, animals. This maximum 

 utilization is sustained, the climax being self-maintaining, and its 

 efficiency is determined by the particular habitat as well as by the 

 average climax population, which in turn is determined by migra- 

 tional possibilities on one hand and, on the other, by all the factors 

 that make up the mature ecosystem. It is evident, however, that, 

 with changes in the environment, plant populations change from 

 one type of area to the next, the vegetation varying largely according 

 to local habitat. That was already indicated above. Consequently, 

 climax and allied vegetation forms a pattern of communities varying 

 with, and largely corresponding to, the pattern of environmental 

 differences and gradients. 



In a general wav climate determines the dominants and associates 

 that can be present, and their life-form in turn characterizes the 

 climax. This is reallv the mature stage of vegetation living in a 



