21 



CALCULATION FOR AVERAGE SAMPLE TREE. 



To find the diameter of tbe average sample tree it is first necessary 

 to find the basal area of its cross section, breast-high. To do this, 

 the basal areas of the cross sections, breast-high, of all the calipered 

 trees must first be found. This is done by finding in the area table 

 (p. 37) the areas corresi)onding to each diameter represented in the 

 calipered trees, multiplying these figures by the number of trees of 

 that diameter and adding the results.* The addition represents the 

 total basal area of the cross sections of all the trees. If, now, we 

 divide this by the total number of trees of the species, we get the 

 basal area of the average sample tree, and from the area table obtain 

 the diameter corresponding to that basal area. 



Applying this method, for instance, to determine the diameter of the 

 average sample tree for the oak, in our area table on page 37, we find 

 that the basal area of— 



Square feet. 



23 oaks of 8 inclies in diameter equals 8. 03 



76 oaks of 9 inches in diameter equals 33. 58 



87 oaks of 10 inclies in diameter equals 47. 45 



172 oaks of 11 inches in diameter equals 113. 52 



43 oaks of 12 inches in diameter equals 33. 77 



97 oaks of 13 inches in diameter equals 89. 41 



115 oaks of 14 inches in diameter equals 122. 94 



84 oaks of 15 inches in diameter equals 103. 08 



164 oaks of 16 inches in diameter equals 228. 99 



181 oaks of 17 inches in diameter equals 285. 31 



46 oaks of 18 inches in diameter equals 81. 29 



67 oaks of 19 inches in diameter equals 131. 92 



88 oaks of 20 inches in diameter equals 191. 99 



118 oaks of 21 inches in diameter equals 283. 83 



78 oaks of 22 inches in diameter equals 205. 91 



32 oaks of 23 inches in diameter equals 92. 33 



4 oaks of 24 inches in diameter equals 201. 06 



85 oaks of 25 inches in diameter equals 289. 75 



2, 534. 16 



The total basal area of the J ,620 oaks equals 2,534.16 square feet. 

 Dividing this area by the number of trees we find that 1.56 square feet 

 is the basal area of the average sample tree which corresponds to a 

 diameter of 16.9 inches. 



SELECTION AND MEASUREMENT OF SAMPLE TREES. 



When the diameter of the sample tree has been determined, a thrifty 

 tree of the species with such a diameter should be selected in the forest. 

 Oare should be taken that the sample tree is not situated in an opening 

 nor on a road nor in a crowded growth -, also that it have an average 

 well- developed crown, and that it be sound, straight, and free from 

 wind shakes. The sample tree so selected is felled, measured, and its 



* The product may be obtained directly from the tables of volume, as explained. 



