THE THEORY AND PRACTICE OF WORKING PLANS 59 



and (3) financial considerations, silvicultural considerations 

 exercising a limiting influence. 



Technical Rotations. — These attempt to produce the max- 

 imum amount of material suitable for a certain purpose, such 

 as railroad ties, mine timbers, saw logs of given size and the 

 like. 



For example, railroad ties can not be made from trees less 

 than 10 inches in diameter breast high. If, therefore, an owner 

 in southern Connecticut desired to grow chestnut sprouts 

 for this purpose it would require fifty * years for the average 

 tree to reach lo inches d.b.h. on the best sites. At this age f 

 there would be 435 standard ties produced per acre besides 35 

 cords of cordwood. 



Another example may be taken from the Pacific Coast. 

 To produce suitable sawtimber from Douglas fir, the tree should 

 be at least 16 inches d.b.h. If, therefore, an owner in western 

 Washington desired to grow Douglas fir for this purpose it 

 would require % seventy years for the average tree to reach 16 

 inches d.b.h. on the best sites. At this age § there would 

 be 56,500 feet, board measure, produced per acre. 



This rotation is the one most commonly used in the United 

 States. It is easily applied and, if conservatively chosen, will 

 give satisfactory results. In this, as in all rotations, the sil- 

 vicultural considerations exercise a hmiting influence. For 

 example, where reproduction is by natural methods, such as the 

 shelterwood method, some of the trees will have to be left beyond 

 the rotation age in order that the seed from them may restock 

 the area cut. This space of time required for the renewal of 

 a stand constitutes the reproduction period and must be added 

 to the rotation age. 



Economic Rotations. — These attempt to secure either the 



* According to Table 17 of Bui. 96, Forest Service, U. S. Dept. of Agriculture, 

 " Second Growth Hardwoods in Connecticut." 

 t Table 28, ibid. 



I Table i, Forestry Quarterly, Vol. XII, p. 442. 

 §Ibid. 



