462 forestry Quarterly. 



buted proportionally to the age classes, or in case of overlapping 

 crowns the excess is properly reduced. It seems as though this 

 principle might be applied in many cases, and it might ultimately 

 serve as the key to the determination of such difficult problems 

 as for instance growth per acre based on age in many-aged 

 stands of Engelmann Spruce. 



The proportion occupied by average crowns can be obtained 

 from the results of the average trees before multiplying by the 

 number of trees in the stand. An illustration of this method is 

 given below. 



Crown space for average mature trees, 1925 sq. ft. 



Crown space for average young tree, 762 sq. ft. 



Proportion of crown space, 2.5 to i. 



Number of mature trees, 66. 



Number of young trees, 262. 



Proportional space for mature stand, 66x2.5=165 



Proportional space for young stand, 262x1^=262 



427 square feet. 

 Resultant proportion of total space: 



165 



For mature or 39%. 



427 "'^^ 



.262 



For young or 61%. 



427 



By these means, a very fair map and division of area between 

 these rough groups may be obtained. The field work proceeds 

 rapidly and will prove to be practical and economical in applica- 

 tion. 



A still further modification of the method of mapping is pos- 

 sible. In mapping areas of veterans it frequently happens that 

 scattered trees belonging to younger age classes stand on blocks 

 that would otherwise be mapped as solid veteran areas. It 

 seems unadvisable to map out the crowns of these small trees. 

 In fact, one of the points in the method is to simplify the map 

 of age classes as much as possible. So the areas are mapped as 

 being occupied by veterans, but the stragglers which do not be- 

 long there are kept in a separate tally. When the areas and 

 number of trees of each age class are determined, it is possible to 



