Investigating Yield Per Acre. 461 



mapped out. Some care was necessary here not to give too much 

 or too Httle area to small timber, but with a little practice it was 

 not difficult to decide on the proper amount of space which was 

 actually claimed by young trees and was not being utilized by 

 older timber. The most difficult problem was presented by groups 

 just maturing, or having a large sprinkling of merchantable trees 

 among a majority of immature trees. Here an arbitrary de- 

 cision was needed, and the area was divided between the age 

 classes according to the best judgment of the investigator. 



The separation of these extreme age classes left the two middle 

 groups occupying the remaining area of the plot. Since the divid- 

 ing line between these was an arbitary diameter limit, it would 

 have been quite difficult to try to sketch in accurately the areas 

 for each of these two "age" classes. So the separation of areas 

 was based on the second consideration, that of relative crown 

 space. The diameters of the crown of a large number of trees 

 of each age class were measured by pacing, one man directing the 

 work from a distance while the other paced across under the 

 crown. The exact area occupied by the crown was not sought, 

 but the average relative area. So, each crown diameter was 

 squared to give it its proper weight on an area basis. The average 

 crown area was then obtained for trees of each age class. This 

 average area must then be multiplied by the number of trees of 

 the class in the plot, and the resultant total represents the areas 

 for each of the two age classes. 



These results give what is wanted, the proportion or per cent, 

 of the acreage, which must be assigned to each age class. The 

 value of this simple method lies in the fact that no attempt is 

 made to measure or assume the actual number of square feet of 

 growing space taken by either the crowns or roots of the average 

 tree of a class. It is merely assumed that the growing space will 

 be proportional to the square of the crown diameters. In multi- 

 plying the diameters squared by the number of trees for both 

 classes, the total area so obtained does not and need not equal the 

 area mapped as being occupied by the sand. But if the one fact 

 holds good, that the proportion existing between the total crown 

 cover for each class can be so determined, all that remains 

 is to multiply the actual total area by the per cent, for the class, 

 to get its acreage. In this way, the blank area is properly distri- 



