12] VEGETATIONAL TYPES OF TEMPERATE LANDS 365 



In the often comparable ' desert steppes ' of the U.S.S.R., which 

 constitute the transition between the more or less continuously 

 vegetated steppes and the deserts of predominantly bare spaces, 

 other Wormwoods {Artemisia spp.) of Sage-brush type tend to be 

 the most characteristic plants. Frequently they are halophytic, the 

 soils being salinized and supporting also such characteristic under- 

 shrubs as Salt-bush {Atriplex caniim). Often prominent in addition 

 are sod-forming Grasses such as wiry Fescues {Festuca spp.) and 

 Feather-grasses {Stipa spp.), and dicotyledonous as well as mono- 

 cotyledonous annuals which develop rapidly with spring rains but 

 die down with the advent of hot weather, so leading an ephemeral 

 life. Examples of this last phenomenon are well seen in desert areas 

 of Iraq — cf. Fig. 156. 



Some Lichens may grow or lie on the surface of the earth, as may 

 Blue-green Algae including colonies of A'ostoc, but arborescent 

 growth, for example of Willows and Poplars, is usually limited to 

 occasional damp depressions or the vicinity of watercourses. Such, 

 for example, are the oases of the Gobi Desert. Rather similar 

 conditions and attendant vegetation, with a dry and generally warm 

 climate subject to sharp contrasts of heat and cold, and one or two 

 brief vegetative seasons each of 1-3 months (in spring and/or 

 autumn) characterized by intermittent rainfall and favourable 

 temperatures, are widespread in temperate as well as in warmer 

 countries. Thus they occur on the plateaux of Asia Minor, in belts 

 around the deserts of Central Asia and Australia, in southern South 

 America and South Africa, and flanking the Sahara and Arabian 

 Deserts. Some of these areas support extensive thorny or other 

 scrub and are apt to be so designated on world vegetation maps. 



These semi-desert regions of both the Old and the New Worlds 

 are typically made up of vast, flat or undulating expanses of bare 

 soil supporting hoary or dull-grey, often sticky and scented, ' heathy ' 

 or sage-like shrubs |-2 metres high. Such shrubs may form a 

 continuous but thin or else broken brush, or be ' scattered ' over 

 otherwise naked tracts, though in particularly arid areas the spacing 

 is often more even and apparently due to root-competition. Al- 

 though there are no green grassy swards there may be bunches of 

 wiry Grasses, and ahhough there are normally no trees there may be 

 tallish Cacti or giant Euphorbias or other large succulents, while 

 saline lagoons, dry most of the year, may be surrounded by fleshy 

 or bushy halophytes. The usually erect or ascending, switchy 

 dominant shrubs often have thickish woody stumps and deep roots. 



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