TRANSITION, ETC. 97 



ages to a timber forest worked by selection is 

 more a change of system than of condition. For 

 both systems we require a forest stocked with 

 trees of all ages, from the seedling to the mature 

 tree ; but while on the one system we cut out 

 some trees of all ages with every coppice rotation, 

 on the other, we cut out annually those trees only 

 which arrive at maturity. But to work a forest 

 methodically, and with uniformity of annual yield, 

 on the system of selection, it is important to 

 determine in how far the areas of trees of each 

 stage of growth are in just relation throughout ; 

 and in the case of great irregularity or preponder- 

 ance of area of trees of any one stage, fellings 

 should be arranged with an -eye to their adjust- 

 ment. The trees should be classed into periods of 

 growth, and supposing we fix these periods at 

 say twenty years, and the rotation at a hundred 

 years, then one-fifth of the area should be occu- 

 pied with trees of each period. With trees of all 

 ages growing promiscuously together, it would be 

 difficult to estimate the relative area of each by 

 ground measurement, but by determining how 

 many trees of each period will flourish on an acre, 

 we know that in the present case we require one- 

 fifth of the determined number of each period. 

 Thus, supposing a forest of such trees as would 

 stand at fifty to the acre in the fifth period 



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