FOREST IN RELATION TO AGRICULTURE 491 



through the New Forest on the Bournemouth road. This is only 

 the effect which is expressed in this difference of temperature : as with 

 other effects, so this one affects the neighbouring lands near the forest. 

 Even a dry wind on reaching a forest must take up some moisture, 

 and thus be less dry when it reaches agricultural land farther on. 

 It can often be seen how the grain in the drier parts of the country 

 planted near the edge of a forest sprouts up sooner than that right in 

 the open. Again, certain crops, such as cacao-yams, cocoa, and Cola 

 trees thrive best amongst trees. Without the forests the Cola planta- 

 tions of the Ilesha district would cease to exist, or at any rate bear 

 very small crops. 



9. The forest increases the humidity of the air. According to 

 accurate measurements taken over a period of forty years, it has been 

 proved that the forest increases the humidity of the air up to 10 per 

 cent. No doubt in man}^ of the Southern parts of Nigeria and the 

 Gold Coast, people travelling in the forests have often thought 

 that there was far too much moisture, not only coming from above 

 and below, but also in the air around them. However, this should 

 not blind us to the fact that further up country this greater humidity 

 of the air of the forest is spread over the adjacent lands, and thus makes 

 possible the growth of agricultural crops, such as cocoa. Cola, yams, 

 and cacao-yams, which would not otherwise be possible. This greater 

 humidity also tends to induce local minor rainstorms, which in their 

 turn benefit the adjacent agricultural land. This greater humidity 

 of the air also tends to prevent the excessive drying in the dry season 

 of the land situated very near, and taken in conjunction with the 

 other factors, such as the regulating of the temperature and the rainfall, 

 makes it possible to put in crops earlier and almost ensures their 

 growing successfully. 



10. The forests prevent the spread of insect and fungoid pests. 

 So often we read that the crops in South Africa or the Argentine have 

 been destroyed by locusts, and on the Gold Coast we read that various 

 pests are destroying cocoa-trees in large numbers. Here, again, a 

 forest or a belt of forests with large numbers of different species of 

 trees interpose a living barrier of green leaf food or woody tissue which 

 these pests may attack, owing to the diversity of the species of trees. 

 Most pests only find a few trees on which they can thrive or reproduce 

 themselves ; thus on reaching the forest the scourge tends to lessen, 

 or even die out. Even in the worst case of large hordes of locusts, 

 it is cheaper to allow them into a forest, perhaps sacrificing it, 

 rather than they should spread further and further over agricultural 

 lands. 



Having shown that it is necessarj' in a new and comparatively 

 unsettled country to preserve a certain proportion of the forests, it 

 remains to be considered what proportion is desirable and necessary 



