VOLUME AND YIELD, SECOND-GEOWTH HEMLOCK. 



41 



was necessary to create an arbitrary standard of merchantable size. 

 It was assumed that in fifty years, the probable shortest time in which 

 land now bare can be logged again with profit, timber will have gained 

 in value sufficiently to warrant the cutting of any tree which will yield 

 a log 20 feet long and 12 inches at the small end. A few of the trees 

 13 inches in diameter breasthigh will contain such a log, but it was 

 thought safer to take 11 inches as the limit. In the subsequent dis- 

 cussion of second growth, therefore, all trees 11 inches and over are 

 considered merchantable, and it is assumed that all timber between the 

 stump and a point 12 inches in diameter inside the bark will be utilized. 



10 



20 



30 



40 



30 



90 



100 



I/O 



120 



60 60 70 



AGE - YEARS . 



FIG. 1.— Diagram showing growth in diameter of second-growth Red Fir and Hemlock in pure stands 



and of Hemlock in mixture with Red Fir. 



Such material as piling or trap poles will be produced in less than 

 fifty years. l)u t earlier than this the trees will not clear themselves 

 sufficiently to make merchantable saw-logs, even if a few reach the 

 requisite size. 



The growth of pure and mixed even-aged forests is very different. 

 In the former, Hemlock grows rapidly, with a normal relation between 

 diameter and height growth. The stand Is exceedingly dense at 

 first, and remains so longer than does a Red Fir forest on account 

 of the greater tolerance of the Ileinloek. The growth in height and 



diameter is also slower than that of Red Fir. Where, however, 



