FOREST ECONOMY. 211 



matter of financial calculation. This calculation is, 

 however, influenced by silvicultural and technical, 

 as well as purely financial, considerations. The 

 fact that the stocks in a coppice lose their vigor if 

 sprouts are left too long uncut, or that frequent and 

 full seed years do not occur until a certain period 

 in the life of the crop, sets limitations to the length 

 of rotation ; the technical value of the product, sal- 

 ability, and market requirements for special materi- 

 als (firewood, poles, mining timber, railroad ties, saw 

 timbers) may influence the choice, but finally quan- 

 tity of product and money yield are determinative. 

 From the standpoint of political economy it was 

 supposed that the largest volume of product per 

 acre per annum, the rotation of maximum volume, 

 should be the aim of forest management, and the 

 rotations chosen for state forests in Germany, 

 which lie mostly between 90 and 140 years, were 

 supposed to be based upon this principle. Lately, 

 however, it has been shown that the largest aver- 

 age product of wood per acre and year occurs much 

 earlier, and usually before much of the crop has 

 attained to desirable size. 



\ Since the accretion of a stand varies from period 

 to period, gradually increasing in rate from its early 

 stages to a given age and then again sinking, there 

 must be a time when the average of all the differ- 

 ent rates, the average accretion, attains its maxi- 

 mum. If, for instance, a fully stocked acre of 

 spruce contained at 120 years io,2CXD cubic feet of 



