12] VEGETATIONAL TYPES OF TEMPERATE LANDS 359 



{Vaccinium spp.), and Bearberries {Arctostaphylos spp.), with a 

 variety of Grasses and sometimes some taller evergreen shrubs. 

 Especially in the North, the heath-like Crowberry {Empetrum 

 nigrum s.l.) is apt to be important and similarly gregarious, as are 

 taller but still low and shrubby deciduous Birches and Willows. On 

 the other hand in the South, the taller shrubs are often evergreen 

 and characteristically have needle-like leaves {e.g. Juniper, Juniperus 

 communis s.l.) or other photosynthesizing members {e.g. Gorse, Ulex 

 spp.). The tendency to be gregarious and mycorrhizal is almost 

 general in these plants : most of the chief dominants at least in the 

 north being moreover evergreen, dwarfed, and richly branched 

 chamaephytes, a characteristic dense and dark mat up to a ^-metre 

 in height commonly results. 



Whereas most low-lying heathlands in temperate regions are 

 subclimaxes of the disclimax type, being due to intensive grazing 

 or recurrent fires that prevent trees from returning to their once- 

 forested areas, in some coastal tracts especially of northwestern 

 Europe these heathlands are evidently maintained through exposure 

 to winds. In such instances they will be in more delicately balanced 

 equilibrium with the environment and consequently more ' natural '. 

 Much the same delicate balance and relative stability probably 

 obtains in many upland areas, where damper peaty ' moors ' are 

 especially common in cool regions — including the ' highmoors ' {cf. 

 Fig. 168) developed on acidic soils inhabited by Bog-mosses 

 {Sphagnum spp.), and the ' meadow-moors ' developed on circum- 

 neutral (usually calcareous) soils. 



Still more important and widespread are grasslands, which indeed 

 in their various forms constitute one of the main ' world ' types of 

 \egetation. Whereas in tropical and subtropical regions grasslands 

 typically take the form of savannas, with widely-spaced trees and/or 

 tall shrubs as described in Chapter XIV, in temperate lands they are 

 usually without trees or bushes except along watercourses. And 

 although many grasslands are due to interference by Man or his 

 domestic animals, many others, including extensive ones in temperate 

 and allied areas, seem to be entirely ' natural '. Thus if they are 

 due to grazing this is, or at all events originally was, apparently by 

 wild animals. 



What seem to be climax grasslands develop in temperate regions 

 chiefly in areas having an average yearly precipitation of between 

 25 and 75 cm. (approximately 10 and 30 inches), or rather more in 

 warm parts. These grasslands occur especially in the interiors of 



