GENERAL RELATIONS. Ill 



Indicator significance of climax formations.— The formation is the greatest 

 of all indicators. In its climax form, it not merely indicates but actually 

 delimits plant climates. In its developmental stages, it sets a definite mark on 

 each successional habitat, and indicates the rate and degree to which these 

 approach the final condition. In practical terms, the climax indicates climate, 

 and its successional stages indicate soil or edaphic conditions. The climax 

 indicates the range of natural and cultural possibilities of a region, the suc- 

 cessions point out the possibilities of localized areas and soils. In a particular 

 locality the climax denotes the general limits of production, and the seres 

 suggest the ways by which maximum production may be reached. Thus, 

 while it is necessary to keep the climatic limitations in mind, the concrete 

 problem in any region is to utilize the indications furnished by the various 

 successions. In the case of agriculture, the facts derived from succession can 

 only be indications, since the vegetation is removed. With grazing and 

 forestry, however, as well as irrigation, reclamation, and many engineering 

 problems, succession itself becomes an instrument by which the desired 

 natural crop can be indefinitely maintained, or by which one crop can be sup- 

 planted by another. 



As stated in a former chapter, succession is the universal key to the prac- 

 tical as well as the technical use of indicators. The stages of a sere are regu- 

 larly linked together in such a definite and organic process of development 

 that the presence of one serves as a record of those preceding and as a pre- 

 diction of those to follow. In every stage lies a record of the past and a 

 prophecy of the future. In practice, this means that a sere can be held in 

 any stage desired, that its progress can be retarded or accelerated, or that it 

 may be destroyed in part or in whole, and a new stage or sere produced. 

 Succession thus becomes a tool of the greatest utility wherever natural crops 

 are concerned. Even in agriculture, it has considerable value quite apart 

 from its indicator significance in meadow and pasture crops and in all those 

 where weeds are a serious factor. It is hardly necessary to point out that such 

 a use of succession is possible only through a good understanding of its pro- 

 cesses. For a complete treatment of this subject, the reader is again referred 

 to "Plant Succession." Here it must suffice to point out the general types 

 of succession and to emphasize their indicator significance. 



Significance of succession. — Since succession is the development, or usually 

 the redevelopment of the climax in a particular spot, it is clear that the actual 

 successions or seres will differ in accordance with the climaxes in which they 

 occur. In other words, each sere is an integral part of the development of the 

 climax and its indicator value pertains primarily or wholly to that climax. 

 As to origin, all seres arise on a bare or on a denuded area. But bare surfaces 

 differ profoundly in nature and hence in the kind of plant community which 

 they can support. Some, such as rock and water, present extreme conditions 

 for plant growth and require a long period of reaction and development before 

 an actual soil is formed and land communities can thrive upon them. Other 

 areas, such as fallow fields and burns, have well-developed soils into which 

 plants can invade immediately. Rock and water are regarded as primary 

 areas, while burns, fields, etc., are secondary ones. A primary area shows a 

 primary succession or prisere, characterized by extreme conditions as to water- 

 content in particular, by a correspondingly slow reaction and soil formation, 



