580 



THE COMMUNITY 



areas, where overcultivation produced de- 

 nudation of natural biotic cover (Sears, 

 1935a). 



Where the secondary effects are not too 

 severe, the area in question passes tlirough 

 a period of arrested or deflected develop- 

 ment, and, when the secondary agency has 

 ceasea to exert a controlling influence, re- 



t\ims to the general pattern of the primary 

 sequence. Under such circumstances the 

 regional edaphic or climatic climax even- 

 tually may be reconstituted. Clements and 

 Shelford (1939, p. 232) point out that, 

 under certain conditions, in subseres there 

 may be regeneration of the climax within a 

 man's Ufetime, or even less. 



30. BIOME AND BIOME-TYPE IN WORLD DISTRIBUTION 



Serai succession and development of 

 communities have been discussed in the 

 preceding chapter. When seres have existed 

 thiough periods of time long enough to be 

 referred to as geologic, the characteristic 

 climatically controlled resulting regions, to- 

 gether with their communities, are referred 

 to as biomes. Biomes may be of great area 

 and of relatively uniform type, especially 

 in their climax communities, but the biome 

 must be understood as including the whole 

 complex of serai stages and edaphic 

 cUmaxes. The classification of these groups 

 of communities involves two higher cate- 

 gories, the biome and the biome-type. The 

 biome-types correspond to the principal 

 cUmatic or physiographic features of the 

 earth's surface. The biome, as just defined, 

 may include also geographically outlying 

 fragments of the same or similar nature that 

 are operationally connected by continuing 

 dispersion of their constituent plant and 

 animal elements; it commonly includes also 

 extensions of qioite variant nature connected 

 by gradual transition with the major area 

 of the biome— for example, the southern ex- 

 tensions of the coniferous forest biome (the 

 taiga) of North America. The distribution 

 of the vegetation of the world, in its larger 

 outUnes, corresponds largely to the biomes 

 of the ecologist. Reference should be made 

 to world vegetation maps, such as those of 

 Goode (1943) and Hesse, Alice, and 

 Schmidt (1947). 



When the biomes of the world as a whole 

 are reviewed, it becomes evident that when 

 operational or transitional connection be- 

 tween otherwise similar biomes is lost, they 

 may be grouped as "biome-types." For ex- 

 ample, we distinguish the biome-type tropi- 

 cal rain forest as including the several major 

 tropical forest biomes, the African, the 

 Oriental and Australasian, the Central and 



South American, and the Madagascan (this 

 list is by no means complete). It is evident, 

 by way of illustration of our differentiation 

 of the biome-type from the biome, that the 

 operational connections and interrelations of 

 the outlying areas of the Congo rain forest 

 are intimate, with only the beginnings of 

 geographic isolation and of endemism pro- 

 duced by isolations, and that the "African 

 rain forest" is properly a single biome. The 

 operational contact between the African 

 and the Amazonian rain forests, however, 

 has been lost for a period of geological time 

 so vast that profound faunal and floral 

 differences have developed. 



The phenomena subsumed in the sere, 

 and the extensions of climax communities 

 with gradual geographic differentiation, 

 complicate the definition of the biome. 

 Nevertheless, these great and somewhat 

 heterogeneous assemblages of communities 

 are easily recognizable as major geographic 

 features; they have been known as fife 

 zones, biotic formations, major biotic forma- 

 tions, "formations" and biomes. The term 

 "biome" is adopted for this work, with the 

 additional "biome-type." 



The relations of the biomes to the major 

 biotic regions have usually not been clearly 

 understood. The concept of the biome is 

 essentially ecological, i.e., operational and 

 contemporary; the concepts "biota," and 

 still more strictly "fauna" and "flora,"* in- 

 volve the historical factor that has produced 

 regional endemism. Confusion between the 

 ecological and biogeographic points of view 

 and their conceptual tools is natural, since 

 faunal and floral areas necessarily overlap 

 the ecological regions (the biomes), and 



* We employ the biogeographic terms biota., 

 fauna, and flora with geographic (and historic) 

 connotation to distinguish them from the more 

 ecologically defined communities and biomes. 



