84 THE SELECTION METHOD 



But in virgin forests (ordinarily considered all-aged) certain 

 of the younger or middle age classes are lacking, or not repre- 

 sented in the right proportion and the stand is apt to be com- 

 posed either of mature trees of about the same height and 

 differing comparatively little in age ^ or else to be of the two- 

 storied character, each story being of practically the same 

 age. Since it is virtually impossible in Nature to find all age 

 classes represented in a single stand, a forest is considered an 

 all-aged or selection forest if a few broad age classes, each of 

 20 to 50 year range, are represented. 



Details of the Method. — In theory the oldest age class is cut 

 each year, the next oldest removed in the following year, and 

 so on indefinitely. Reproduction springs up in the openings 

 immediately after cutting. By the time all the age classes in 

 an all-aged stand have been cut over once seedlings started on 

 the area occupied by the age class which was cut first will 

 have matured. Thus in a true selection stand an old age 

 class ripe for cutting will be available each year. (See Fig... 

 25 and Fig. 26.) The volume of this age class will be equiva- 

 lent to the annual growth of the stand. Each age class should 

 occupy its proper per cent of the area. For example, if there 

 are a hundred age classes, each class should have one hun- 

 dredth of the crown space allotted to it; and then if one 

 hundredth of the area, in this instance, is each year, actually 

 cleared of trees or uncovered, only the trees belonging in the 

 oldest age class will be removed. Since the trees making up 

 the oldest age class are scattered it is necessary to work through 

 the whole stand to find them and to conduct logging opera- 

 tions over the whole area each year. 



In practice certain changes in this theory are demanded 

 both from the logging and the silvicultural standpoints. The 

 annual working of the whole area to secure a small cut per 

 acre makes logging relatively expensive. Seed trees do not 



