THE SELECTION SYSTEM 47 



cent, of the area, and the other classes should have 

 enough trees so that, as each comes to maturity, it will 

 occupy 20 per cent, of the area. 



In making selection cuttings in this ideal forest, the 

 oldest age-class would be removed during the first 20 

 years. Then the trees in the next age-class would begin 

 to come to maturity, and would be cut during the fol- 

 lowing 20 years. If successful reproduction were se- 

 cured, this process might be continued indefinitely. 



The theory of the selection system is illustrated on 

 page 46. Fig. 10 represents a fragment of a selection 

 forest just before cutting. The trees designated as "I" 

 are mature, and are therefore removed. Fig. 11 shows 

 the same stand after 20 years. The trees marked "II" 

 in Fig. 11 are now grown into the mature class, and 

 are ready for cutting. All trees have grown both in 

 height, diameter, and crown surface. Several trees have 

 disappeared as a result of the mutual crowding. Small 

 groups of young seedlings are found growing in the 

 openings made by cutting. 



In some cases a stand is cut through every year. In 

 the theoretical example this would mean cutting each 

 year one-twentieth of the oldest age-class. Usually it is 

 impracticable to make annual cuttings, and the stand 

 is cut through periodically. The interval between 

 cuts may be called the cutting cycle. In Europe, the 

 cutting cycle is usually about 10 years. In this counrry 

 the interval between cuts will more often be from 20 

 to 50 years. 



