THE THEORY AND PRACTICE OF WORKING PLANS 



107 



where the allowed cut ought to be distributed among the differ- 

 ent classes, and what proportion of the old, medium, and young 

 trees it should contain. The most favorable distribution among 

 the different classes of the whole, according to M. Gurnaud, 

 is 50 per cent in the old tree class, 30 per cent in the medium 

 class, 20 per cent in the young class. In the following cases, 

 it may be advantageous to change these proportions; for 

 example, to increase the proportion of older trees if the soil 

 needs protection, or to lessen the older classes according to species 

 and exposure, if more sunlight is needed for the appearance 

 of natural reproduction. This method is much less a method 

 of absolutely mathematical results, appUcable to all forests, 

 than a simple process allowing the finding of all necessary 

 information in the forest. 



(b) Example. — A typical stand of Western yellow pine 

 of 456 areas * was measured in 1909 and remeasured five years 

 later with the following results: 



1909 



1914 



Increase 

 in five years. 



Number of trees 4 inches or over, d.b.h. 

 Total volume, ft. b. m., 1 2 ins. or over, d.b.h. 



8,25s 

 1,550,910 



8,400 

 1,756,328 



145 



205,418 



Total increment for five years = 13.2 per cent == 2.64 per cent 

 per year. The curreiit annual increment per cent of this stand 

 is therefore 2.64 per cent. The annual cut would therefore be 

 taken as 2.64 per cent of 1,756,328 board feet =-46,367 board 

 feet. This is an equivalent of 102 board feet per acre. By 

 Von Mantel's method the cut, assuming a rotation of 160 years, 



would be ^'75 ^3^ =21,954 board feet, which is far lower 

 80 



than the circumstances warrant. By method No. 4, including 



* Data from " A PreUminary Report on the Progress in the Remeasurement of 

 Sample Plots on the Coconino and Tusayan National Forests, Arizona," by G. A. 

 Pearson, briefed For. Quart., Vol. XIII, No. i, pp. 60-63. 



