162 WEST AFRICAN FORESTS AND FORESTRY 



greater supervision and more stringent forest regulations than in the 

 ordinary leased areas, on the whole his prospects of getting out greater 

 quantities of timber more expeditiously and cheaply are much greater 

 than in the ordinary areas. 



Particularizing some of the great concrete objects for which reserve 

 is made : 



Firstly, the permanent supplies of timber of all kinds, with a view 

 to turning out approximately the same quantity year after year in 

 perpetuitj^ — in fact, if anything, gradually increasing the output year 

 after year. This means to say that, although the forest is cut down, 

 it is replaced at the same rate at which it is cut down. Putting it in 

 another way, there must be as many blocks, or portions or actual 

 " stands " in the forest as represent the number of years which elapse 

 between the time a tree is planted and the time it is cut down. This 

 period is known to foresters as " the rotation," and in northern temper- 

 ate countries, for Coniferous trees the time is usually reckoned at about 

 80 years. In the tropics, with mahogany, Iroko and other timbers, 

 it may be only necessary to allow 60 years, or perhaps on very poor 

 ground 100 years. In the case of teak in Burma, a rotation between 

 80 and 100 years is perhaps about sufficient to enable merchantable 

 timber to be produced. Putting it in another way, in the forest, 

 in order to have the permanent yield, there must be sufficient trees 

 of each girth class, so that when the largest, saj^ those over 12 feet in 

 girth, are cut down, there must be sufficient of those between 10 and 

 12 feet, which will grow during a 10-year period (in which they are 

 cut) from 10 feet to 12 feet in girth. At the present time it has been 

 found convenient to classify each class as " under 2 feet, 2 to 4 feet, 

 4 to 6 feet, 6 to 8 feet, 8 to 10 feet, 10 to 12 feet, and over 12 feet." 

 The object of this is to clear away, or have cut, all those trees over 

 12 feet in girth. This makes room for younger, quicker-growing timber. 

 Although, under the Nigerian Forest Law, the girth of mahogany has 

 been reduced to 11 feet, and in some districts to 10 feet, eventually, 

 as the older and more unremunerative slower-growing trees are cut 

 down, it will be possible to reduce the girth still further. To put this 

 question of the permanent yield in yet another way : All the trees 

 from one year old, or from the smallest size to those over 12 feet in 

 girth, represent what we may call the forest capital. Now, the object 

 of the rotation is only to take the interest on this capital ; that is to 

 say, the amount which grows on all the trees over the whole area for 

 one year. It would, however, not do to clip off little pieces from each 

 tree over the whole area, as they would be quite useless as timber. 

 Therefore this amount is calculated out as so many cubic feet per 

 annum, or so many trees above a girth of 12 feet or 11 feet, or whatever 

 the girth limit may be, and this amount, either in cubic feet or in the 

 number of trees, is allowed to be cut down each year. Then we know 



