Normal and Actual Forest, Etc. 



157 



But just as the normal yield table is useful as a table of growth, 

 etc., so the model or normal forest is useful far beyond the mere 

 comparison of the conditions of age classes. It is the only means 

 of learning the relations of growth, growing stock and yield 

 from a forest business imder given conditions. 



'r-Yj 



The simple triangle is stiU one of the most helpful diagrams 

 used in the study of forestry. And it makes little difference 

 whether we are satisfied to take G„, the normal growing stock, as 



r 

 being equal to Y,X— or whether we calculated it from the yield 



tables. 



In any case we get a normal growing stock to which the actual 

 growing stock in any given forest may be compared. Naturally, 

 where satisfactory jdeld tables are still wanting and where we 

 can decide on the rotation and on the yield of a fuUy stocked 



r 

 mature stand (Y^.) the simple: Gn = Y;.XT will have preference. 



But once Y,. and r are decided upon or, what amoimts to the 

 same thing, when we decide upon the normal average yearly 

 growth per acre and the rotation, the value of G„ is fixed. Merely 

 as an aside, it may be said that a reasonable figure for Y, is easily 

 secured from the usual cruise, while a satisfactory growth study 

 of stands of different age from one to r takes much time and money 

 and deserves little confidence unless it agrees closely with figures 

 based on Y,. 



From the very nature of the growing stock as a growing crop 

 of plants, it is evident that any modification in amount or character 



