THE CLIMAX. 105 



Of all the initial stages, the first is in many ways the most significant. In 

 consequence, it seems desirable to distinguish it as the jrioneer stage. This 

 term is most applicable to the extreme conditions of a primary area, though 

 two kinds of pioneer stages may well be distinguished, as already suggested. 

 Lichens, on the one hand, and submerged plants on the other, are the usual 

 pioneers for rock and water seres respectively. For the present it seems best 

 to designate only the first initial associes of the primary sere as the pioneer 

 stage, and to leave the further distinction between actual and normal pioneer 

 stages for future needs. The case of the first stage of secondary seres is differ- 

 ent, however. The initial conditions are rarely extreme and the invasion is 

 correspondingly extensive and rapid. The invaders do not meet pioneer con- 

 ditions in the sense of primary areas, and the first stage is very short, often last- 

 ing but a year or so. The degree of occupation is usually high and the number 

 of stages so few that only the first one can be regarded as initial. As a conse- 

 quence it seems desirable to speak of a pioneer stage only in primary succession, 

 and to designate the opening stage of a secondary sere as the first or initial stage. 



Medial stages. — The general demarcation of these from initial stages has 

 been sufBciently indicated above. They are characterized by a fairly uniform 

 density, by well-developed dominance, and usually by the increasing abun- 

 dance of hvunus, together with medium amounts of water. They consist of 

 well-developed communities in which layers have begun to appear. The 

 most characteristic life-forms are grasses and shrubs. Medial stages may 

 best be regarded as including all the stages between initial and climax ones. 

 In all seres but those with a forest climax this is aU the stages after the initial 

 ones but the last. When succession ends in forest, it seems desirable to con- 

 sider aU the successive forest conmiunities as climax stages, though only the 

 last is the climax association. The number of medial stages is several in pri- 

 mary seres, and few, often only one or two, in secondary ones. In both the 

 term must be regarded as comparative and relating chiefly or solely to position 

 in the sequence, since grassland stages are medial in a region with a forest 

 climax, and climax in a climatic grassland region (plate 29, a, b). 



THE CLIMAX. 



Concept. — ^Every complete sere ends in a climax. This point is reached 

 when the occupation and reaction of a dominant are such as to exclude the 

 invasion of another dominant. It does not prevent the entrance of subordi- 

 nates, and it is conceivable that a codominant might enter also, though no 

 case of this is known. The climax marks the close of the general develop- 

 ment, but its recognition is possible only by a careful scrutiny of the whole 

 process. Duration is in no wise a guide, since even pioneer stages may persist 

 for long periods, and medial stages often simulate a climax. The test of devel- 

 opment is especially necessary in climax stages, i. e., those in which the domi- 

 nants belong to the same life-forms as the climax dominant. It is not merely 

 indispensable to trace and retrace the course of succession in a particular 

 locality. It is also imperative to follow the development in all parts of the 

 climatic region where dominants occur which are similar to the one supposed 

 to be the climax. There is no field in ecology where it is so necessary to employ 

 both intensive and extensive methods to secure permanent results. The 

 reason for this is obvious when it is fully recognized that the climax formation 

 is the clue to all kevelohment and structure in vegetation. 



