Chapter XII 



VEGETATIONAL TYPES OF TEMPERATE 

 AND ADJACENT LANDS 



We now come to what in some respects is our main objective — ■ 

 the study and interpretation of the vegetation and its component 

 communities inhabiting different areas of the world. It should, 

 however, be remembered throughout the following treatment that 

 the various types of vegetation described are merely those which 

 we recognize, almost all being apt to intergrade with little or no 

 distinction or even characterization. These intergradings and also 

 the relative positions of the main vegetational types will of necessity 

 be largely ignored in the following brief treatment, although the 

 geographical situation and main neighbouring types in each instance 

 can be noted in a general way from the map facing page i of the 

 text, which is a highly generalized vegetation map of the world. 



We have seen that the systematic relationships of the flora of a 

 region depend to a considerable extent upon its geographical con- 

 nections or barriers, whether past or present ; on the other hand 

 the physical characteristics of the vegetation are largely conditioned 

 by local environmental factors. Thus when two areas have been 

 separated since far back in geological time by such barriers as wide 

 seas which cannot ordinarily be crossed by plants, their floras (of 

 component species, etc.) will often be very different, whereas if 

 their environmental conditions are similar their vegetation in closely 

 comparable habitats is likely to have the same general appearance. 

 This is because similar external conditions which make up particular 

 habitats tend to produce communities (and life-forms as regards 

 component plants) whose external physical features are much alike 

 — however dissimilar may be their more fundamental reproductive 

 and allied structures by which we usually classify them. For this 

 reason we expect — and generally find — in hot arid habitats succulent 

 plants belonging to very various families, in moist temperate regions 

 deciduous trees, and on high mountains dwarf shrubs and perennial 

 herbs of tussocky growth. Nor does it matter in this connection 

 whether or not the areas concerned are separated from one another 



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