38 BASES AND CRITERIA. 



In one sense, however, the distinction may possess some value. This is with 

 reference to the factors which give character to the great areas marked by 

 climaxes, in contrast to localized ones occupied by successional stages. It 

 is more or less convenient to refer to such areas as climatic or edaphic, if 

 it is recognized that the one denotes a permanent condition over a wide region 

 and the other a relatively transitory stage in a restricted area. 



Moreover, the grouping of factors as physical and biotic appears to have 

 little value beyond that of mere classification. Furthermore, it does not con- 

 duce to clear thinking to use the same causal terms for the physical conditions 

 which control plants and animals, and for the plants and animals themselves. 

 With the growing recognition of the community as consisting of both plants 

 and animals, the true nature of biotic factors will become evident, and they 

 will be recognized as reactions. 



Climates and habitats. — If one accepts the developmental basis for the study 

 of vegetation, he must also admit the same process in habitats. Habitat and 

 community develop reciprocally from extreme conditions to the final climax 

 controlled by the climate. At this point climate and habitat become merged 

 and are coextensive with the major community, the climax formation. In 

 this connection, however, it is necessary to discard our ordinary ideas of climate 

 and to accept the plant's view of what constitutes a climate. The fact has 

 been appreciated by Wojeikov especially, in his work on the climate of beech 

 (1910). The great grassland climax of North America lends particular 

 emphasis to the difference between climates as determined by plants and by 

 man. In the human sense the climate of southern Saskatchewan is very 

 different from that of northern Arizona, chiefly because of temperature, yet 

 Bouteloua gracilis is an important grass in both places and the grassland 

 formation is characteristic of both regions. Likewise the Palouse district of 

 Washington and Idaho with its winter rainfall seems wholly different from 

 the bunch-grass hills of Utah and the prairies of Nebraska; but if the vegeta- 

 tion be taken as the indicator of climate, all three are essentially the same, 

 since they are characterized by prairie associations (Weaver, 1914, 1917). 



The acceptance of the climax climate as the major or climax habitat enables 

 us to establish a perfect correlation between habitat and vegetation. The 

 climax habitat will show divisions corresponding to the association, and each 

 association habitat will exhibit subdivisions in agreement with the consocia- 

 tions. This is practically axiomatic, since each community is the product of 

 the factor complex of its habitat. The habitat of one association must neces- 

 sarily differ from that of another to the degree that one association does from 

 the other. The subordinate communities of a formation, viz, societies and 

 clans, also have their minor habitats, though these are less clearly marked, as 

 would be expected. The structure of the climax climate or habitat corre- 

 sponds closely if not exactly with that of the climax formation. It may be 

 best illustrated by the grassland climax with its five associations, namely, the 

 true prairie, mixed prairie, bunch-grass prairie, the short-grass plains, and 

 desert plains. While all of these fall in the same climax climate, each one 

 marks a corresponding division of it, or a subclimate. In the case of the true 

 prairie, there are five dominants or consociations, Stipa spartea, S. comata, 

 Agropyrum glaucum, Koeleria cristata, and Andropogon scoparius, no two of 

 them exactly equivalent as to habitat. Their requirements approach each 



