464 Forestry Quarterly. 



a tree of a given diameter can have but one volume in the table. 

 The point on this curve of height and volume, which coincides 

 with the volume in board feet, of the average tree for the class, 

 indicates the average diameter, and this diameter in turn gives 

 the age by either of the two methods described, namely either 

 from felled sample trees or by using an age curve. 



With age determined, the yield per acre of each of three age 

 classes is determined for the forty — or twenty-acre plot studied. 

 Twenty acres is a large enough plot except in very open, old or 

 irregular stands. These data give three points in a yield table. 

 Since the sizes, average volume, and age of these rough age 

 classes will differ on each forty, there is no difficulty in getting 

 enough points for a curve of yield based on age. 



This system was first tried at Doucette, Texas, in 1909, in Long- 

 leaf Pine, and was described in the Fore:stry Quarterly (vol. 

 VII, 385ff.) in that year. It has since been tested on Longleaf 

 Pine at Clarks, La., in 1910, on Shortleaf Pine at Trinity, Texas, 

 in 191 1, and, in the present year, on Shortleaf Pine at Crossett, 

 Arkansas. Each year, the method has shown the same flaws and 

 the same strong points, and each year it has been possible to get, 

 by its use, a yield table which in its general results, bears a 

 striking similarity to those of the other seasons. In other words, 

 the method works, whatever its faults. 



The flaws lie in the apparent fact that at several stages the re- 

 sults obtained may be greatly altered on the same plot by differ- 

 ences in judgment of different crews. Wide latitude is allowed 

 as to what shall constitute a veteran tree, and what range of 

 diameters shall be included in young timber. Then in mapping, 

 crews may differ radically in their judgment of areas to assign to 

 veterans, or to immature timber, so much so that the resulting 

 yields may bear very little resemblance to each other. But the 

 strong points of the method lie in the fact that errors are re- 

 vealed by the method itself. The most serious error is in mapping 

 the areas ; all other parts of the problem take care of themselves, 

 if only reasonable care is used. But it is possible, especially the 

 first time the method is tried, to be greatly deceived as to the 

 actual facts, and to note too much or too little area on the map 

 for a given age class. If this is done on a twenty acre plot, 

 when the zvhole area is distributed between the different age 



