390 Forestry Quarterly 



He points out how rapidly stem numbers are reduced by the 

 prescribed thinnings — accentuating the findings of the above brief 

 on spacing ! On good soil the stem number per acre for spruce is 

 around 2400 in the thirtieth year, and 240 in the eightieth year, 

 hence in the intervening 50 years 90 per cent are removed in 

 thinnings, only 10 per cent are left for final harvest. In volume 

 the product in 80 years will have been 14,000 cubic feet, of which 

 40 per cent, or 5600 cubic feet, will have been removed in thin- 

 nings and 60 per cent, or 8400 cubic feet, are final harvest. 



From decade to decade, beginning in the thirtieth year the 

 thinnings reduce the number on the average each time by one- 

 third, or more precisely by 40, 36, 30, 30, 30, and 25 per cent, if 

 the final harvest takes place in the eighty-fifth year. Similarly 

 with pine on good sites, the number is reduced from 2,000 in the 

 thirtieth to 160 in the hundredth year and to 120 in the 120th 

 year; that is 92, or 94 per cent, goes into thinnings, only 8, or 6 

 per cent respectively, remain for final harvest. For oak, the re- 

 duction is even greater, namely from 1600 to 100 and 80, or 6.25 

 and 5 per cent remain in the hundredth and 120th years respec- 

 tively. Nevertheless, the volumes in both species at the two 

 rotations, are nearly alike, namely 5,000 or 5700 cubic feet for 

 the two rotations. 



In beech, which starts with a specially large number of stems, 

 97 per cent may go into thinnings. 



Management under severe thinnings in the subdominant brings 

 out interesting relationships between number, basal area and vol- 

 ume: when 30 per cent of the number is removed, Vm of that 

 per cent, or 21 per cent, is removed of the basal area, and *'/io, or 

 18 per cent, of the volume. This holds in a general way for 

 spruce, pine, beech and oak. 



If managed under a moderate thinning, the percentages are 

 lower, namely Vi„ and ^/j,, respectively for basal area and volume, 

 so that if 20 per cent of numbers were removed this would in- 

 volve 12 per cent of area and 10 per cent of volume. Generally 

 speaking, the severer the thinning, the more the stouter stem 

 classes are involved in it, the nearer to each other stand the 

 per cents of number, area and volume. 



Thinning in the dominant and leaving the subdominant undis- 

 turbed produces opposite relations, namely higher area and vol- 

 ume per cents. Thus to a 15.4 per cent removal of numbers in a 



