FORESTRY 1 87 



of deficiency varies greatly. In the absence of fundamental know- 

 ledge regarding the role of forests in conserving water-supplies and 

 soil, referred to above, it has been necessary to adopt arbitrary 

 criteria in determining the areas to be reserved, such as a fixed 

 percentage of the total land area; the separate reserves are care- 

 fully selected with regard to their distribution over the whole 

 territory. 



The extensive reservation of large blocks of country as conserva- 

 tion forests is always expensive, so that it is desirable that reserved 

 areas should be worked to provide some revenue, provided that 

 (a) there is sufficient demand for timber to warrant exploitation 

 and (b) any working is on a basis of sustained yield, with regenera- 

 tion and tending of forest keeping pace with cutting. The clear 

 felling and replanting of areas, which is a commonplace of forestry 

 in temperate climates, is rarely adopted in Africa except as a last 

 resort, because in any tropical or sub-tropical forest only a small 

 proportion of the trees are commercially valuable, and on account 

 also of the detrimental effect of tropical sun and rain on a bare 

 forest soil. The eventual ideal would be for nearly all reserved 

 forests to be brought under working plans, ^ so that conservation 

 can go hand in hand with exploitation and regeneration. Working 

 plans belong, however, to a late phase in the evolution of forestry: 

 the immediate needs in Africa are the conservation of the remain- 

 ing forests and the development of forest uses. 



The principal agent in modifying the original forest vegetation 

 of Africa is the native practice of shifting cultivation, which is often 

 aided by fire. Apart from the destruction of valuable forest, this 

 practice has resulted in places in serious erosion and degradation 

 of the soil. This is particularly noticeable in hilly regions such as 

 Nyasaland, where A.J. W. Hornby (1923) has described the results. 

 As the population increases and the available areas of forest de- 

 crease, the results will be more and more serious, and yet the forest 

 areas are the only reserves on which agriculture can draw for its 

 expansion in many parts of the continent, and some experts are of 

 the opinion that shifting cultivation in a modified form will always 

 be the mainstay of native agriculture. 



* 'Working plans' is an expression used in forestry to imply a detailed programme of 

 felling and regeneration, including replanting where necessary. 



