332 BRAUN 



desirable method of study. Once the community relations have been deter- 

 mined, isolated samples of community types from other areas may be used 

 to amplify concepts. 



What are the concepts which can be illustrated by a dynamic approach to 

 such a forest study as the above? (1) An association concept — for here are 

 more or less well-defined communities, each with definite dominants and 

 seemingly more or less in equilibrium with the habitat. (2) A succession 

 concept, based on evidence of change, of lack of accord of canopy and under- 

 story, and of forces, here largely biotic, at work directing the changes. (3) A 

 climax concept, for this succession appears to end in a self-perpetuating com- 

 munity. Will these concepts as first developed stand the test of application 

 to other unlike sites in the geographic region and of application in other 

 geographic regions? In part, yes; in part, no. 



In unlike sites of the same geographic area, the communities are different, 

 the causal factors of succession may be different, and topographic change 

 rather than biotic direct the course of development. And still, communities 

 are evident — let us for the present call them associations; succession is evi- 

 dent, and a climax is reached — but not a beech climax. At once we question 

 our climax concept. The beech forest of our example is dependent on a par- 

 ticular site — an undissected plain in an immature topography. With the first 

 development of drainage lines, changes begin again and development goes 

 on. This beech forest is a physiographic cUmax. The climax of mature topo- 

 graphic sites is different and more enduring. 



Soon we realize that no two pieces of vegetation are exactly alike, even 

 though they may have the same dominants. Nichols (1923) realized this and 

 proposed the association concrete (applied to a piece of vegetation) and the 

 association abstract — the abstract concept gained by familiarity with many 

 pieces of similar vegetation. Gleason (1926), recognizing unlikeness, sug- 

 gested the individualistic concept. 



In other geographic areas, we find again that concepts must be revised. 

 The seemingly important associations of our local area are not found; a mul- 

 tiplicity of new ones occur. Succession may be less evident — not because suc- 

 cession is not or has not taken place, but because development of primary 

 vegetation has progressed farther, or in some instances because development 

 has been interrupted by frequent disturbance. Climax communities may be 

 found which bear a marked resemblance to those of mature topography of 

 our local area. Such climax communities begin to assume greater importance 

 in our thoughts. We begin to understand Clements' views, which resulted from 

 extensive work. We realize that our association concept is open to question, 

 that there is a tremendous difference between the pin oak association, or the 

 white oak association, or even the beech association, and the climax association 

 which we find recurring again and again over a vast geographic area and as 

 a result of many unhke lines of succession. Clements (1916) proposed the 



