158 SYLVICULTURE IN THE TROPICS R . n 



after the clearing has been completed. In many ways 

 it would be better to cut them before the clearing has 

 been begun, as they would check the rush of water from 

 any showers from the outset ; but, on the other hand, 

 they would soon get choked by debris washed into them, 

 and much labour would have to be expended in 

 cleaning them out. As it is, a certain amount of this 

 has to be done after the first heavy fall of rain. It is 

 necessary to see that the drains are kept free and 

 function properly until the young plants have formed 

 leaf-canopy, when, owing to the shelter given to the 

 ground by the crowns and by dead leaves and other 

 detritus, the rush of water will be reduced and the 

 young trees will be strong enough to withstand the 

 pressure of flowing surface water. 



All draining operations are expensive, and before 

 undertaking them it is advisable to consider carefully 

 the possibility of avoiding them. Small swampy places 

 may often be left unafforested, or it may be possible to 

 put in species which can live in such soil, and, on steep 

 slopes especially, total clearing of the soil may be 

 avoided and clearing in patches substituted. 



In an arid locality, and particularly on a soil which 

 does not retain moisture, it may be necessary to employ 

 irrigation to start the young plants, and even, in some 

 cases, this irrigation has to be continued throughout 

 the life of the trees. This is of course very expensive, 

 and can only be justified under special circumstances. 

 The Changa Manga plantation, which was started to 

 supply fuel to the town of Lahore in India, and which has 

 been raised on a very porous soil, is an example of this. 



For small areas, the methods of irrigation described 

 in the chapter on Nurseries will suffice, but for larger 

 areas larger works are necessary, a full description of 

 which does not belong to a volume of the nature of 

 this, but to special treatises on irrigation. 



The system of distribution is generally the reverse 

 of that adopted for drains. The main canals take up 

 the water from a river, lake, or tank. From these 



