100 STABILIZATION AND CLIMAX. 



as plants are evolved or conditions changed. Fortunately, our real concern 

 with stabilization is limited to the degree in which it appears in each sere. In 

 other words, it requires study as a developmental phenomenon, and not as 

 a more or less active condition. 



LIFE-HISTORY STAGES. 



Nature. — While the movement from initial stage to climax or subclimax is 

 practically continuous, there are typically certain periods of comparative or 

 apparent stabilization. These correspond to population or invasion maxima, 

 which mark more or less well-defined stages or communities. As noted else- 

 where, such stages usually appear much more distinct than they really are, 

 owing to the fact that the study of succession so far has been little more than 

 the arrangement in probable sequence of stages contemporaneous in different 

 areas. However faint their limits, real stages do exist as a consequence of 

 the fact that each dominant or group of dominants holds its place and gives 

 character to the habitat and commimity, until effectively replaced by the next 

 dominant. The demarcation of the stages is sharper when the change of 

 population is accompanied by a change of life-form, as from grassland to scrub 

 or forest. In some secondary seres there is little or no change of life-form and 

 the stages are few and indistinct. In rare cases the dominants of the entire 

 sere may be present the first year after a bum, for example, and the well- 

 marked stages are due solely to the rate of growth, which causes the dominants 

 to appear and characterize the area in sequence. 



Kind of stages. — Stages may be distinguished upon various bases. The 

 most obvious distinction is based upon change of population. This is the 

 readiest method, but also the least significant, unless it takes account of domi- 

 nance as well. Change of life-form is more fundamental and equally conven- 

 ient, while change of the habitat is even more significant, though much harder 

 to recognize. Dominance, with reaction, includes all of these bases, and is by 

 far the best method. The essential stages are those marked by a dominant 

 or group of dominants. For complete analysis, however, it is desirable to 

 recognize other stages, such as those based upon population and upon effective 

 change of habitat. For general purposes, also, it is convenient to distinguish 

 stages with reference to their_ position in the course of development. As a 

 consequence, the best method of treatment is to base stages upon successive 

 dominants and to recognize substages whenever a change of character makes 

 it desirable or necessary. This is usually in the early part of seres, before 

 dominance is clearly established. At the same time it is helpful to group 

 stages for reference or to bring out certain relations. They may be grouped 

 intojnitial, medial, or final, or into temporary or migratory, on the one hand, 

 and permanent, stable, ultimate, or climax on the other. As to habitat, one 

 primary sere, for example, may show rock, gravel, grassland, and woodland 

 stages, and another water, sedgeland, grassland, and woodland. The corre- 

 sponding life-form stages would be Kchen, moss, herb, grass, scrub, forest, and 

 algse, herb, sedge, grass, scrub, forest. 



Role of life-forms. — Since dominance and reaction are consequences of the 

 life-form, it follows that the main stages in development are marked by differ- 

 ent life-forms. The latter is used in a broader sense than is usual; it includes 

 not only the vegetation form, with its synonyms, biological forms, growth- 



