26 



sample trees is exactly the same as that which exists between their 

 corresponding basal areas; hence, dividing the basal area of the whole 

 forest by the basal area of all the sample trees, and multiplying the 

 quotient thus obtained by the volume of all the sample trees, the grow- 

 ing stock of the forest is determined. This method requires neither 

 calculations to determine the dimensions of the sample trees nor the 

 separate measuring of each to determine the volume. All the sample 

 trees of the corresponding diameters are directly selected in the forest, 

 felled and sawed into logs of desired length, which logs are piled 

 together and the volume of the pile determined as a whole in cords or 

 in cubic feet. Or else the number of superficial feet of all the sample 

 trees can be accurately and directly obtained by sawing the logs into 

 boards and other kinds of lumber. 



The choice of the per cent or the proportion of trees to be taken as 

 sample trees is influenced by the accuracy to be attained and the size 

 of the area to be measured. If a tolerably satisfactory representation 

 is to be had, not less than 10 to 15 trees, or at least 1 per cent, should 

 be used. 



Suppose that in order to determine the volume of the 1,620 oaks of 

 our hard- wood grove, recorded in Form No. 1 (p. 19), it was decided to 

 take 1 per cent, or in all 17 sample trees. If the fraction is less than 

 one-half it is disregarded; if more than one-half it is considered as one. 

 Then the number of sample trees for the oak would be determined as 

 follows : 



23 trees of 8 inches diameter require i^fo — do sample tree. 



76 trees of 9 inches diameter require -,^o-o — one sample tree. 



87 trees of 10 inches diameter require i^oV — one sample tree. 



172 trees of 11 inches diameter '"equire jH — two sample trees. 



43 trees of 12 inches diameter require i^o'^t- — no sample tree. 



97 trees of 13 inches diameter require i^oV) — one sample tree. 



115 trees of 14 inches diameter require Jo u — one sample tree. 



84 trees of 15 inches diameter require -po^o — one sample tree. 



164 trees of 16 inches diameter require +§^ — two sample trees. 



181 trees of 17 inches diameter require |§n — two sample trees. 



46 trees of 18 inches diameter require -i^oi) — iio sample tree. 



67 trees of 19 inches diameter require -i^J^,7— one sample tree. 



88 trees of 20 inches diameter require -^%^a — one sample tree. 



118 trees of 21 inches diameter require t^^ — one sample tree. 



78 trees of 22 inches diameter require i-o^o — one sample tree. 



32 trees of 23 inches diameter re(][uire -i=\fo — iio sample tree. 



64 trees of 24 inches diameter require -nro — one sample tree. 



85 trees of 25 inches diameter require -^sfo— one sample tree. 



The 17 sample trees of the corresponding diameters are then si lected 

 in the forest, felled, and sawed up into logs, which are piled together 

 with the tops of all the sami)le trees. Let the pile be equal to 6^ cords, 

 or 832 cubic feet. Let us suppose that the 6i cords were sawed into 

 lumber and furnished 3,360 feet B. M. From the measurements with 

 the calipers, recorded in Form No. 1, we know the basal area of the oak 

 to be equal to 2,534.16 square feet; the basal area of 17 sample trees we 



