378 SCIENCE IN AFRICA 



Other parts of the continent are not so well placed, however, 

 and districts can be selected where there has been a scarcity of 

 land for a very long time. One or two instances have already been 

 cited, but another worthy of mention is the Kikuyu reserve, 

 where, as the Kenya Land Commission pointed out, the native 

 population have destroyed increasing areas of forest throughout 

 the few hundred years they have been in Kenya. As an example 

 from West Africa, the densely inhabited district of Owerri in 

 Southern Nigeria, where there are upwards of three hundred 

 people per square mile in some parts, is suffering from pronounced 

 pressure of population in spite of abundant rainfall well distributed 

 through the year. In parts of Northern Nigeria, especially in 

 Sokoto and Katsina Emirates bordering the Sahara, the reserves 

 upon which over-concentrated populations draw for land can only 

 be the forest areas which should be the heritage of posterity. 



Conditions vary so much from place to place that generaliza- 

 tions on this subject are difficult, but it is clear that shifting cultiva- 

 tion is a principal obstacle to the conservation of forests, as stressed 

 in Chapter VII. Where the choice of an area to be cleared lies 

 between virgin high forest or regenerated bush forest, the native 

 will nearly always choose the former because the soil is more fertile 

 and free from weeds of cultivation. The choice is tempered by the 

 kind of timber required for domestic purposes; since house-build- 

 ing requires straight poles, young forests may be preferred to ancient 

 high forest. Fire is a principal element in clearing operations and 

 the brushwood is invariably burnt on the spot. The wood ash 

 adds to the soil fertility and the burning causes a partial steriliza- 

 tion of the soil, and temporarily checks the growth of weeds, so 

 that heav}^ weeding may not be entailed for one or two years. In 

 shifting cultivation the growth of weeds is often a cause for leaving 

 the land equal in importance to loss of soil fertility. 



The degree of destruction in making clearings varies consider- 

 ably among different tribes. The stumps of trees and bushes are 

 usually left in the ground since they do not impede cultivation 

 with the hoe. This sometimes facilitates regeneration of forest, 

 when the plot is deserted, but if soil erosion has set in during the 

 intervening period, regeneration is greatly retarded. Some tribes 

 appear to realize the necessity of maintaining tree growth on their 



