332 INTRODUCTION TO PLANT GEOGRAPHY [cHAP. 



What may well be the true situation is expressed by Professor 

 H. J. Costing, in the work cited at the end of the last chapter, as 

 follows : 



' The Clementsian interpretation postulates that a climatic region has 

 but one potential climax ; the most mesophytic community that the 

 climate can support. It will be found on sites with average or in- 

 termediate environmental conditions, particularly regarding moisture 

 relations . . . Given sufficient time, with accompanying stability of 

 climate and land surfaces, succession will have proceeded to such 

 terminal, relatively mesophytic communities over much of the area. 

 The stands will not be identical, yet they will have such a high degree 

 of similarity that they are obviously related . . . The concept of a 

 regional or climatically controlled climax necessarily includes recogni- 

 tion of the convergence of successional trends toward a similar end. 

 In its simplest statement, it implies that any habitat in a region, given 

 enough time, could ultimately support a community representative of 

 the formation. From this statement it might be inferred that a region 

 of fairly uniform climate would eventually have a continuous and equally 

 uniform vegetational cover throughout. Actually, this is never true 

 . . . Locally, there are always edaphic or physiographic situations 

 whose complex of environmental factors differ to such a marked degree 

 from those of the general climate that they cannot support the regional 

 vegetation type and probably never will . . . Monoclimax theory does 

 not ignore these extreme situations but rather emphasizes that they are 

 to be expected.' 



In any case the main, apparently climax, vegetational types of the 

 world are regional and climatic to the extent that they tend to recur 

 on favourable soils more or less throughout a region of particular 

 climate ; they are also apt to have their counterparts in regions of 

 different climate. These main types of vegetation are characterized 

 by the life-form of the dominant or co-dominants and include : 

 (i) tropical rain forests, the most luxuriant vegetation of all ; (2) 

 tropical forest with a seasonal rhythm, due for example to monsoons ; 

 (3) sclerophyllous forest, developed where there is a hot dry season 

 and a cooler moist one, often merging into various parklands and 

 savannas, which appear to belong rather with grasslands ; (4) warm- 

 temperate rain forests, of evergreens, where there are few if any 

 frosts ; (5) deciduous summer forest, with dominants losing their 

 leaves in winter ; (6) northern coniferous forests, dominated mostly 

 by evergreens ; (7) heath, dominated by members of the Heath 

 family or heath-like plants such as Crowberry ; (8) tundra, the very 

 variable but more or less continuous, treeless vegetation typical of 



