microstands in a mosaic or complex may be grouped into a 

 microcommunity-type; thus mosaics or complexes may be con- 

 sidered to consist of several kinds of microcommunity-types, and, 

 obviously, they may also be classified into higher categories on 

 the basis of similarity. 



For each stand and community-type, in addition to an analysis 

 of the intrinsic characteristics, a description is needed of the 

 habitat, the position on environmental gradients, and, whenever 

 possible, the successional status. A description of the habitat 

 should include at least a general statement about temperature 

 and precipitation, topography, nature of the substratum includ- 

 ing a profile description, and an appraisal of limiting or critical 

 factors. The successional status of various stands ranges from an 

 early stage in primary or secondary succession to the climax. Con- 

 sequently, the dynamic or syngenetic position of every commu- 

 nity needs to be considered, especially the development or growth 

 from a young to a mature stand, succession or the replacement 

 of one stand by another, and the evolution or changes in the com- 

 munity by means of the genie modification of constituent species 

 that occurs, as well as the other changes discussed in Chapter 5. 

 Since mutations apparently do not, as a rule, persist in natural 

 vegetation, it can be expected that a community will be long- 

 enduring provided that the environment does not change greatly, 

 but alteration of the environment or in the kinds and numbers 

 of species in the stand may give opportunity for mutations to be- 

 come established. Studies in dynamics require the preservation 

 of samples of natural communities, not only for the maintenance 

 of gene pools, but also because the complex interrelationships of 

 the organisms in each have required a long period of inter- 

 coordinated ecologic evolution which cannot be duplicated by 

 man. 



CRITERIA OF CLASSIFICATION (SYNSYSTEMATICS) 



Many kinds of plant communities, differing in magnitude and 

 complexity, may be found in any country, and almost instinc- 

 tively one tends to place them in groups, such as forest, grassland, 

 or weedy wasteland. The human mind apparently demands 

 orderliness, so classification is more than a convenience, ^°° it is an 



Bases and Units * 175 



