486 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



dian, Transition, and Upper and Lower Sonoran. His latitudinal 

 counterpart for the Arctic-alpine Zone was the Tundra. In this zone, 

 presumably, the climate did not permit the permanent development of 

 trees. He was particularly interested in explaining the distribution of 

 birds and animals on the basis of these vegetation zones. 



While Merriam greatly oversimplified the geographic relationship 

 of plants and animals to their environment by focusing only on cli- 

 mate, he is to be credited, nonetheless, with making the first serious at- 

 tempt to interpret Si'ogeography climatically. He was a bit short 

 sighted, however, when he wrote, "It appears, therefore, that in its 

 broader aspects the study of the geographic distribution of life in 

 North America is completed. The primary divisions and their sub- 

 divisions have been defined and mapped, the problems involved in the 

 control of distribution have been solved, and the laws themselves have 

 been formulated." His "laws" have never enjoyed wide acceptance, 

 but his Life Zone concept and terminology are still quite useful for 

 general descriptive ecology, especially in montane areas for which, 

 after all, they were first formulated. 



The well-known plant ecologist F. E. Clements was also greatly 

 impressed by the correlation of vegetation and climate, and he de- 

 veloped a whole new school of ecology, founded on the now classic 

 concepts of "succession" and "climax." These concepts had from 

 the beginning a far wider application and validity than Merriam's 

 Life Zone concept, and they are still widely held despite rather severe 

 criticism in recent years by phytosociologists. In Clements' view, 

 there was on any newly exposed land surface, such as a glacial moraine, 

 a more or less orderly succession of vegetation types from the ac- 

 cidental first colonizers through to an ultimate mature type, which 

 attained a dynamic equilibrium with the regional climatic regimen and 

 was subject to no further important changes so long as the climate 

 didn't change. This succession was regarded as a very long-term pro- 

 cess that could only culminate after the climate had succeeded in 

 bringing about general physiographic uniformity, including a mature 

 soil. Persistent local variations in soils or topography, for example, 

 could arrest the plant succession at any given stage and put off the 

 the arrival of the final one indefinitely. The final stage was termed the 

 climax, and it was postulated by Clements that those regions with 

 the same climate ultimately developed the same vegetation climax. 

 The major plant formations of the world, such as the coniferous Boreal 

 Forest and the Tundra, were seen, then, as climax types. Thus, the 

 so-called "Tundra Formation" represents a climax without trees, 

 which presumably will always develop under the influence of the 

 arctic-alpine climate. 



