48G WEST AFRICAN FORESTS AND FORESTRY 



go so far as to put a " Ju-ju " on the land, which is in effect a notice 

 to say that the land is of no use for a farm. However, this is usually 

 forgotten in a generation, so that the same thing may happen again, 

 only that insufficient time has elapsed for a proper forest to be grown, 

 as the cutting of the original forest may have so altered the climatic 

 factors of the locality that not only different species of trees but also 

 grasses have come in, and choked nearly all the self-sown forest- 

 tree seedlings. The main beneficial effects of the forest may be 

 summarized as follows : 



1 . The rainfall of the locality is increased, according to the figures 

 of the Indian rainfall stations. This may amount to as much as 

 16 to 28 per cent, increase on the annual rainfall. 



Afforestation on the Russian steppes has shown that more rain 

 now falls on the planted area than in former years. 



In Western Canada it is generally said that its climate is altering, 

 and a general increase of rain has been noticeable since plantations 

 have been made on thousands of farms and what forests there were 

 originally have been rigorously protected from annual fires. 



2. The rainfall both above and in the ground is more regularly 

 distributed. 



First of all, nearly 23 per cent, of the rain which falls on the trees 

 in a forest is re-evaporated into the air and does not reach the ground 

 at all. This in itself increases the humidity of the atmosphere, tends 

 to form clouds, and thus induces further rainfall. The clouds tend 

 to protect the plants from excessive sun at what may be a critical 

 period in the growing season. The extra humidity of the atmosphere 

 does not necessitate the plants transpiring so much moisture as they 

 would otherwise have to do, to keep them in growing condition. 

 Compared to that in the open, only 22 per cent, of the amount of 

 evaporation takes place in the forest, added to the fact that it occurs 

 under the canopy of the trees, thus creating the more humid atmo- 

 sphere which is so suitable, for instance, for the growth of cocoa and 

 other such crops. In other words, we can take one hundred parts 

 as the amount evaporated in the open, of which not a quarter is 

 evaporated in the forest. Again, as we have seen, twice as much 

 of the rainfall soaks into the ground in the forest as in the open, and 

 owing to the tree-roots and general covering of the soil the water 

 can only flow away gradually. On the other hand, in the open, if the 

 ground is at all sloping, more than half of the rain which falls to the 

 ground runs away immediately, or lies on the land, flooding it and 

 making planting impossible. 



The trees then act as a rainfall distributer and also as a rainfall 

 regulator. The roots of the trees act like a sponge, absorbing a great 

 deal of the rainwater besides preventing it from running away. It 

 has been calculated that it takes nearly six months for the rainfall 



