A NATIONAL PLAN FOR AMERICAN FORESTRY 



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youth but slows down at about the same time as decay is accelerating. 

 Finally, a point is reached in highly defective stands at which volume 

 of decayed wood increases more rapidly than volume of sound wood, 

 and the stand suffers an increasing net loss year by year. This 

 condition is shown in figure 1 for white fir in California where between 

 the ages of 280 and 300 years, loss from decay offsets the amount of 

 new wood added to the tree. For Douglas fir in western Oregon and 

 Washington on good sites, loss from decay at 100 years on the average 

 is 1 percent, at 200 years 8 percent, at 300 years 18 percent and at 

 400 years 36 percent; at 300 years the volume increase in decay 

 equals the volume increase in sound wood, and from that age on 

 stands suffer an increasing net loss. These two examples serve to 

 illustrate the general principle, but so far investigations have made 

 this information available wholly or in part for only a few species, 



GROWTH OF NEW WOOD 

 DEVELOPMENT OF DECAY 



80 



100 120 140 160 ISO 2OO 220 24O 26O 280 30O 320 340 

 AGE CLASS (YEARS) 



FIGURE 1. Rate of increment of decay in white fir (California) . Through youth and middle age the growth 

 of new wood is much more rapid than the development of decay. Above the age of 280 years the 

 increase in decayed wood exceeds the total increase in tree volume for the same period. 



notably western white pine in northern Idaho, quaking aspen in 

 Utah and Minnesota, and incense cedar in California, in addition to 

 white fir and Douglas fir previously discussed. 



The fact that decay increases with age of stands makes the method 

 for prevention of serious losses obvious ; that is, determine the age for 

 each species at which decav becomes of economic importance, and 

 cut the trees before this age is reached. In addition, in order to intel- 

 ligently handle the overmature, highly defective stands now existing 

 with the minimum loss, it is necessary to know the rate of decay at 

 different ages for the component species, so that those stands in which 

 the most rapid loss is occurring can be first harvested where possible. 

 Then, too, it is necessary to understand the outward indications of 

 decay in standing timber, so that timber estimating may be placed 

 on a more exact basis, since logging operations are based on the amount 



