76 NOTES ON FORESTRY. 



years' rotation, which latter is indeed but a trifle 

 higher than is to be got from a twenty years' rota- 

 tion. What, then, is the inducement to protract the 

 period ? 



This is readily rendered intelligible. At fifty 

 years we may suppose there were 125 trees, 60 

 feet high and a foot diameter at breast-high, 

 giving 2000 cubic feet; at 120 years we may 

 estimate 75 trees, a foot and a half diameter at 

 breast-high and 90 feet high, giving 4000 cubic 

 feet. (This is taking *33 as the form figure.) 



Now these 125 trees would taper to 6 inches diame- 

 ter at 30 feet, leaving 125 spars, 30 feet long and 6 

 inches diameter at base, unsaleable as timber, while 

 the 75 trees in the longer rotation would only 

 taper to 6 inches at 60 feet, leaving only 75 spars, 

 30 feet long and 6 inches at base, as unsaleable. 

 This would leave 325 cubic feet waste, or about 

 15 per cent, on the 2000 cubic feet, and 187 cubic 

 feet, or a little less than 5 per cent, on the 4000 

 cubic feet. 



Moreover, between the 50th and 120fch years, 

 50 trees, equal approximately to 1500 cubic feet, 

 have been thinned out. 



On the fifty years' rotation the saleable timber is 

 2000 325 = 1675, or 33 cubic feet per annum, 

 and on the 120 years' rotation, 4000 - 187 = 3813 + 

 1500 for thinnings, giving a total of 5313 or 44 



