Chapter XIII 



VEGETATIONAL TYPES OF POLAR LANDS 

 AND HIGH ALTITUDES 



The Arctic and Antarctic make up the ' polar lands ' and are 

 roughly those lying, respectively, north or south of the limit of 

 arborescent growth, even as the high altitudes here considered are 

 those above the timber-line. This ' tree-limit ' approximately 

 coincides with a mean temperature of io° C. (50° F.) for the warmest 

 month (normally July in the Arctic). Actually, though use of the 

 tree-limit is a great improvement on the astronomically determined 

 but biologically misleading arctic and antarctic circles, satisfactory 

 delimitation of the Arctic and Antarctic can scarcely rest on such 

 a simple basis ; nevertheless for our present purpose it will suffice to 

 tell us approximately what to consider in this chapter, and what 

 to exclude. 



Beyond the stunted ' elfin wood ' and twisted ' Krummholz ' that 

 top the upper timbered slopes of mountains in forested regions, or 

 the usually more open ' taiga ' that terminates the poleward limit of 

 forests, is normally a zone of relatively luxuriant ' tundra '. This, 

 by definition, is treeless, though in its most southerly tracts it may 

 contain shrubby examples of the forest dominants as well as, in 

 favourable situations there and elsewhere, bushes of other sorts. 

 The great and extensive examples are afforded by the Arctic, the 

 Antarctic having relatively little ice-free land apart from scattered 

 islands, and the high-alpine tracts being also limited. Consequently 

 most of this chapter is concerned with the Arctic, followed by 

 briefer mention of some antarctic and high-alpine features which 

 are often comparable — without, however, being by any means 

 identical. 



If we recognize some modern refinements' the Arctic may be 

 generally characterized as treeless, with the winters largelv dark and 

 cold and the mean temperature of the warmest month plus one-tenth 

 of the mean of the coldest month over a cvcle of years not more 



^ Auggested, for example, in the Journal of Ecology, vol. 39, pp. 308-315, 

 1951- 



380 



