FOREST COMMISSIONERS REPORT. 



91 



Table 2. — Volume groxvth of paper birch. 



* The rate of growth given in this table was determined b.v dividing the in- 

 crease in volume during tho different flve-year periods by the volume at the 

 beginning and at the end of the period and by averaging the results obtained to 

 And the rate of growth at the middle of the period. This gave the rate of 

 growth for the five-year period, whicli was divided by 5 for the annual rate of 

 growth. These values were then plotted on cross-section paper and smoothed 

 out by means of a curve. 



and represent very well average conditions. These figures 

 should, therefore, give a good idea of the average rate of 

 growth of paper birch throughout Maine and New Hampshire. 



It is evident from these tables that the height growth of the 

 sprouts is more rapid throughout life than the height growth of 

 the seedlings. The difference between the two is relatively 

 greater in early youth, but absolutely is about constant. 



The difference in diameter growth is not so constant. Up to 

 45 years of age the sprouts have a greater diameter than the 

 .seedlings, at 45 the diameter is the same, while after that the 

 .seedlings have the greater diameter. In other words, while the 

 sprouts make a greater diameter growth at first, this rate is not 

 maintained, and the seedlings gradually overtake and pass them. 



In volume the sprouts surpass the seedlings throughout life. 

 The difference is not great at any point, and averages only a 

 little more than i cubic foot. It is enough, however, to indicate 

 that the encouragement of second growth sprout stands may 

 often be advantageous, particularly for short rotations and when 

 large-sized material is not .specially desired. The decrease in 

 rate of growth of l)(>th seedlings and sprouts with advancing 

 age is partly counterbalanced by the better quality of the wood, 

 which, on account of its freedom from knots, is much more 

 valuable tlian the earlier growth. After 55 years of age. how- 



