APPLICATION OF RESULTS TO FOREST 421 



The difference between this volume and the total actual stand is d — ac and repre- 

 sents the surplus volume in the older trees, of which there are y. The difference 

 in volume for each tree is 6 — o, and for all of the older trees is (6 — a)y. 

 Then 



(b—a)y=d—ac; 



and 



d — ac 



y = l ' 



o—a 



while 



x = c—y. 



Having the values, or number, of each group x and y, the total volume is obtained 

 by multiplying this number by the volume of the average tree for the group. 



Illustration, Western Yellow Pine. 



Total volume in group (<*) =27,042,800 feet B.M. 

 Total number of trees (c) =44,423. 

 Age of older trees, veterans, chosen as 300 years. 

 Age of younger trees, mature, chosen as 200 years. 

 Diameter, from curve of growth, veterans, 27 inches. 



mature, 20.7 inches. 

 Volume of average tree of this size, veterans 805 feet B.M. 

 mature, 340 feet B.M. 

 Then 



(1) 340a; +805?/ = 27,042,800 feet B.M. 



(2) 3403+3401/ = 340 c. 



= 15,103,820 feet B.M. 

 Subtracting (2) from (1) 



465j/ = 11,938,980 feet B.M. 

 y = 25,675 trees; 

 x = 18,748 trees. 

 Volume of younger class = 6,374,320 feet B.M. 

 Volume of older class =20,668,375 feet B.M. 



322. Application of Results to Forest by Use of Stand Table and 

 Per Cent. It is not necessary that a 100 per cent tally of the number 

 of trees, and total volume for the site be obtained, but only that the 

 stand table (§ 188) from which the determination is made be representa- 

 tive of the total area. 



If in the timber survey, 5 per cent of the area is covered and assumed 

 to represent the average stand, the total count of trees on this 5 per 

 cent and the total estimate on the strip, give the data needed. If, 

 in turn, but 10 per cent of the strip itself or t^ of 1 per cent of the total 

 area is tallied, and this per cent gives the run of sizes of the timber 

 without reference to its density of stocking, the data are still sufficient. 



To obtain the separation of the total stand by means of the data 

 from the smaller area counted, the volume of each age class is first 

 expressed as a per cent of the total. These per cents are then applied 

 to the total estimated volume on the entire area. 



