Il8 SCIENCE IN AFRICA 



forests on rainfall have led to inconclusive results. Deforestation 

 probably does not diminish the actual annual rainfall, but it 

 nevertheless produces drought. When forest cover is removed the 

 rainwater, instead of percolating slowly into the soil and draining 

 gently into the rivers, tends to flow away rapidly and violently, 

 causing soil erosion and temporarily extensive flooding. Eventually 

 large tracts of country, which were formerly well watered, become 

 arid.i 



Whether or not Africa, as a whole or in part, is undergoing 

 progressive desiccation, one conclusion seems certain: the drought- 

 stricken parts of Africa are in no position to meet a possible pro- 

 longed cycle of drier years. If these came, all the various factors 

 of drought here mentioned would, unless countered, be intensified 

 in a vicious circle of interacting effects that might cause extensive 

 depopulation. 



BIOCLIMATOLOGY 



The w^ord bioclimatology is used to describe the general study 

 of the effects of climate on life. One aspect of bioclimatology is 

 concerned with the 'ecoclimate', or the meteorological conditions 

 occurring in a particular limited environment, such as a bush or 

 cubic metre of atmosphere overlying soil. Such variations are 

 often of a surprisingly large order; hence the objection to the pre- 

 viously used term 'micro-climate' with its implication of minute 

 variations. In reality any climate is made up of a number of 

 ecoclimates, and large-scale representations are merely approxi- 

 mations of value in comparing one area with another, or tracing 

 the differences associated with seasons. From the biological point 

 of view, moreover, the changes in climate from hour to hour and 

 from day to day are often of as much importance as seasonal 

 changes. 



The study of ecoclimates has scarcely yet come into prominence 

 in Africa, but the work accomplished shows to how great an extent 

 insects and other organisms may depend on slight changes in 



* The subjects touched on here are treated in more detail as follows : — Influence of 

 forests and other vegetation on rainfall in Chapters vi and vii, pp. i6i, 178, etc.; soil 

 erosion in Chapter v, p 136. 



