VIII. DIRECTION OF DEVELOPMENT. 



Development always progressive. — Succession is inherently and inevitably 

 progressive. As a developmental process, it proceeds as certainly from bare 

 area to climax as does the individual from seed to mature plant. While the 

 course of development may be interrupted or deflected, while it may be slowed 

 or hastened, or even stayed for a long period, whenever movement does occur 

 it is always in the direction of the climax. In this connection, however, it is 

 imperative to distinguish between the development of the sere and the action 

 of denuding agencies. This is particularly necessary when such a process as 

 erosion acts with varying intensity in different portions of the same area. 

 At first thought it seems permissible to speak of such a commimity as degen- 

 erating or retrograding. A closer analysis shows, however, that this is both 

 inaccurate and misleading. What actually occurs is that the community is 

 being destroyed in various degrees, and secondary areas of varying character 

 are being produced. In these, colonies appear and give a superficial appear- 

 ance of regression, but in no case does actual regression occur. In every 

 denuded area, no matter how smaU, development begins anew at the stage 

 determined by the degree of denudation, and this development, as always, 

 progresses from the initial colonies to or toward the climax formation. 



Nature of regression. — Regression, an actual development backwards, is 

 just as impossible for a sere as it is for a plant. It is conceivable that lumber- 

 ing, grazing, and fire might cooperate to produce artificial regression, but there 

 is nowhere evidence that this is the case. Apparent regression would, and 

 probably does, occur when the forest canopy is removed by the ax and the 

 shrub layer is also later removed as a consequence of grazing or fire, permitting 

 the final establishment of herbland or grassland. Here, however, there can 

 be no question of development, for the whole process is one of destruction, of 

 partial denudation. The consocies resemble those of the final stages of the 

 original sere, but are largely or wholly different as to the constituent species. 

 The actual condition is one characterized by the removal of the dominants and 

 the consequent change of the controlling conditions. The latter results in the 

 disappearance of many principal and secondary species and the concomitant 

 invasion of new ones. As long as the artificial forces which brought this about 

 persist or recur, the community will be held in a subclimax, i. e., the develop- 

 ment is checked in much the same way that extreme cold or wet stops the 

 growth of the individual plant. Once the inhibiting forces are removed, 

 normal development is slowly resumed and progresses to the proper climax, 

 provided the climax community still persists in adjacent areas (plate 44, a, b). 



The apparent exception afforded by the Sphagnum invasion of grassland or 

 woodland communities is discussed a little later. Here again a close scrutiny 

 of the facts indicates that this is but another case of local and partial denuda- 

 tion due to water. The case is complicated by the fact that the growth of 

 Sphagnum is both a cause and a consequence of the increased water and of the 

 resulting denudation by overwhelming or flooding. Successionally, Sphagnum 

 stands in the same causal relation to the flooding that a beaver-dam or local 

 surface erosion does. It is both a cause and a pioneer, however, and this dual 

 r61e has tended to conceal the essential relation. 



145 



