FOREST IN RELATION TO AGRICULTURE 487 



to come out in the springs of a forest. This also to some extent 

 accounts for the saying that if the wells are full in October in the 

 Temperate Zone, or at the end of March in the Tropical Zone, there 

 will be sufficient water the whole year round. With a varied dis- 

 tribution of forests in the country, the above two effects are naturally 

 felt on neighbouring agricultural land, and in many cases make 

 possible the growing of certain crops, such as cocoa. Cola and rubber, 

 which otherwise could not be attempted. An interesting example 

 of this is seen in the way in which the natives of Ilobe, in Nigeria, 

 have planted Cola trees just inside and on the edge of the Ilaro Forest 

 Reserve boundary. 



3. The forest protects the land against corrosion. In most 

 countries, wherever the ground is sloping and bare the annual fall 

 of rain washes away large masses of good soil as well as stones and 

 other debris, in many cases destroying pasturage or agricultural 

 land, and in any case silting up the rivers with sand-banks and bars, 

 thus hindering navigation. It has often been said that, for its size, 

 the CVoss River carries in the rainj^ season much more material in 

 suspension and rolled along its bed than many other African rivers. 

 The main reason apparently for this fact is that several of its tribu- 

 taries, such as the Mbu, the Fi, the Mfu and the Bago, rise at what 

 are now partially grass-covered mountain slopes, but which no doubt 

 were a short time ago covered with fine evergreen forests. 



The immediate effect of clearing such slopes is that the water, to 

 the extent of nearly 90 per cent., rushes unchecked down the mountain 

 slojDe, gaining momentum with every mile and taking grass, soil and 

 even whole mountain slopes (1,500 feet in height) along with it. On 

 the other hand, if such slopes are covered with forest trees 25 per cent, 

 of the rainfall is re -evaporated into the air before reaching the ground, 

 10 per cent, is evaporated from the ground into the air of the forest, 

 and fully 65 per cent, soaks into the ground. 



An instance of this last effect can be seen in the Cross River Divide 

 from the Bambuto Mountains, on the Nigerian border. In a few 

 places the native farmers understand this effect and make the 

 terraces on which they plant parallel with the contour of the hill-side ; 

 however, this is insufficient when the whole mountain slope has been 

 cleared of forest. Only a definite distribution of the land between 

 forest and farm would prevent the undue corroding of hill- sides. The 

 unrestricted rush of the rainwater off the hill-sides has yet a further 

 effect on the lower ground of the country, in that it causes the streams 

 and rivers to flood and overflow their banks. This, in turn, prevents 

 huge acreages of land from being cultivated for many months in the 

 year, and other large areas lower down from being cultivated at all. 



Yet another effect is that a vast mass of water hurries down into 

 the sea where it is not required, and where there is already plenty of 



