LAWS OF DIAMETER GROWTH IN MANY-AGED STANDS 357 



276. Laws of Diameter Growth in Many-aged Stands, Based on 

 Diameter. When diameter growth is studied in order to determine 

 the age of trees of given diameters, the basis of the average is entirely 

 different from that required when the diameter or size of trees of given 

 ages is required. By the inspection of Fig. 71, it will be seen that 

 when based on age for each decade, several different diameter classes 

 are averaged together. The average diameter even for the oldest 

 age class is several inches less than the maximum diameters reached 

 by the dominant trees. To prolong a curve of growth based on age 

 until the diameter of the maximum tree is reached, would add several 

 decades to the apparent age of a tree of this diameter. 



On the other hand, if diameter is actually the basis and the average 

 age is sought, the classes included to obtain these averages are read 

 horizontally in Fig. 71 and include under the same diameter several 

 different age classes. The principal effect of this difference in the basis 

 of averaging is found when the larger diameters are reached. In 

 stands composed wholly of intolerant trees, where suppression and 

 prolonging of the life cycle is not a factor, the difference between the 

 age of the larger, dominant diameter classes which exceed the average 

 and the average age of smaller diameter classes, which include many 

 trees fully as old as the dominant classes, is much less than would be 

 indicated by a curve based on age. A curve showing the average age 

 of trees of given diameter is not expected to show the progress of trees 

 in diameter from dec- 

 ade to decade, but 

 expresses directly the 

 result of the total 

 growth or period for the 

 specific class of trees 

 concerned. 



There is but one 

 way to determine ac- 

 curately the average 

 age of trees of separate 

 diameter classes and 

 that is by a total count 

 of rings for several trees Fig. 73.— Ages of trees of different diameters, shown 

 in each diameter class for two groups of longleaf pine, the first com- 

 to obtain the average posed of second-growth stands, the second of 

 age directly on this veteran or old-growth timber, 

 diameter basis. When 



these points or averages are plotted, they will show a relation about 

 as indicated in Fig. 73. 



