444 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



mally these tall woody plants are more or less widely scattered except 

 in unusually favourable circumstances such as obtain along water- 

 courses or elsewhere that water is relatively plentiful. The occur- 

 rence of more hygrophilous ' meadows ' is rare in the tropics and 

 is clearly due to some particular local factor or factors of disturbance. 



Although many grasslands in the tropics, as elsewhere, appear to 

 be ' natural ' to the extent that they do not owe their existence to 

 direct interference by Man, it now seems clear that there is no such 

 thing as a ' tropical grassland climate ' and quite possible that 

 tropical grasslands are not in fact climatic. This may even be the 

 case with the savannas which in one form or another constitute 

 their most common expression, for in the tropics taller woody plants 

 are rarely absent from such areas. Certainly many of these tracts 

 owe their persistence or very existence to fires or browsing animals, 

 or are edaphic climaxes due to local soil conditions, while others 

 appear to be serai. Thus fires often destroy woody and other 

 dicotyledonous plants and Palms without appreciably damaging the 

 underground parts of the Grasses. But whatever their ecological 

 significance may be, these grasslands constitute characteristic types 

 of considerable economic as well as areal importance. 



Savannas or their treeless counterparts are very widespread in 

 tropical and subtropical regions, where they often cover vast tracts — - 

 though not without considerable local variation within their own 

 areas, as in the cases of many South American ' campos ' and 

 ' llanos '. Examples are to be seen in southwestern North America 

 and the West Indies, in Central and South America both north 

 and south of the Amazonian forests, and in very many parts of 

 Africa such as the Sudan and within as well as around the closed 

 forests of the Congo, etc. They also occur in central Madagascar, 

 in disturbed and upland areas of India and elsewhere in Asia, and 

 to the north of the central desert tracts of Australia. The climate 

 is hot, with a moderate range of temperature and a fair rainfall 

 often exceeding lOO cm. annually and well spread over 120 to 190 

 days, during which ' rainy season ' large areas may be constantly 

 under water. On the other hand there is a prolonged drought 

 lasting often for six or seven months of the year, and a tendency to 

 desiccating winds. With such substantial rainfall, more or less 

 xerophilous woodlands are apt to predominate in the absence of 

 disturbance — at least elsewhere in areas of very high temperatures 

 and prolonged rainless periods during the vegetative season. These 

 woodlands may include the savanna-woodlands, which are dis- 



