
ESTIMATING STANDING TIMBER. ae) 
of the tract. The total yield for each type is obtained by multi- 
plying the contents of the average acre by the total number of 
acres covered by the type. This type method of cruising is par- 
ticularly applicable to regions like the southern Allegheny Moun- 
tains, where the character of the timber situated in the coves and 
on the flats and gentle slopes is quite different from that in other 
situations. 
COMPUTATION OF RESULTS. 
No explanation has yet been made of how the average vield per 
acre is computed aiter the measurements are secured. This is 
done in two ways: 
(1) The yield of each acre is computed separately and all are 
averaged together; or (2) a model acre is constructed by adding 
together the number of trees of each diameter which occur on 
all the sample plots and dividing the result by the number of 
plots, which gives the average number per acre oi trees of each 
diameter. For example, to construct a model acre the average 
number of 6-inch trees on all the acres measured is calculated; 
then the average number of 7-inch trees; then of 8-inch trees, of 
9-inch trees, ete. The result is a model acre having the average 
number of trees of each inch diameter. Only one computation of 
vield is then required, and this will represent the average oi all the 
sample acres. 
The method of computing the contents of a model acre or of any 
sample acre depends upon whether or not height measurements 
have been taken. If heights have been disregarded, the compu- 
tation may be made in the following way: 
Make four columns of figures as shown below. In the first 
column place the diameters, in the second column the number of 
trees of each diameter, in the third column the average contents of 
trees of different diameters, and in the fourth column the total 
contents of all trees of each diameter, which is found by multi- 
plying together the values in the second and third columns. The 
figures in the fourth column are then added together for the total 
contents of the acre. 

