VI. STABILIZATION AND CLIMAX. 



Stabilization. — The progressive invasion typical of succession everywhere 

 produces stabilization. The latter is the outcome of greater occupation due 

 to aggregation and migration and of the resulting control of the habitat by 

 the population. In other words, stabihzation is increase of dominance, cul- 

 minating in a stable climax. It is the mutual and progressive interaction of 

 habitat and community, by which extreme conditions yield to a climatic 

 Qptimuin and life-forms with the least requirements are replaced by those 

 which make the greatest demands, at least in the aggregate. So universal 

 and characteristic is stabihzation that it might well be regarded as a synonym 

 of succession. It has the advantage of suggesting the final adult stage of the 

 development, while succession emphasizes the more striking movement of 

 the stages themselves. 



Causes of stabilization. — The essential cause of stabilization is dominance. 

 The latter is partly due to the increasing occupation of a bare area, but is 

 chiefly the result of the life-form. The occupation of armuals in an initial or 

 early stage of a secondary sere is often complete, but the dominance is usually 

 transient. Effective dominance can occur only when the prevailing life-form 

 exerts a significant reaction, which holds the population in a certain stage 

 until the reaction becomes distinctly imfavorable to it, or imtil the invasion 

 in force of a superior life-form. Dominance is then the ability of the charac- 

 teristic life-form to produce a reaction suflBlcient to control the community 

 for a period. Dominance may mean the control of soil factors alone, primarily 

 water-content, of air factors, especially hght, or of both water and light. 

 Initial life-forms such as algse, Uchens, and mosses are characteristic but not 

 dominant, since the reaction they produce prevents control rather than gives 

 it. This is the essential difference between the initial and the final stages of 

 succession. While both react upon the habitat, the reaction of the one favors 

 invaders, that of the other precludes them. The reactions of the intermediate 

 stages tend to show both effects. At first the reaction is slight and favors 

 the aggregation of occupants; then it becomes more marked and produces 

 conditions more and more favorable to invasion. On the other hand, when 

 the reaction is distinctly unfavorable to the occupants, the next stage develops 

 with greater rapidity. Each stage is itself a minor process of stabilization, a 

 miniatm'e of the increasing stabihzation of the sere itself. Reaction is thus 

 the cause of dominance, as of the loss of dominance. It makes clear the 

 reason why one community develops and dominates for a time, only to be 

 replaced by another, and why a stage able to maintain itself as a chmax or 

 subclimax finally appears. Thus, reaction furnishes the explanation of stabih- 

 zation, as it does of the successive invasions inherent in succession (plate 

 26, A, b). 



Relation to the climax. — ^The end of the process of stabihzation is a climax. 

 Each stage of succession plays some part in reducing the extreme condition in 

 which the sere began. It reacts to produce increasingly better growing condi- 

 tions, or at least conditions favorable to the growth of a wider range of species. 

 This is equivalent to reducing an excess of water-content or remedying a lack 

 of it. The consequence is that the effect of stabilization on the habitat is 

 98 



