Apr. 1, 1925 
The Construction of Taper Curves 
611 
ings, large limbs, forks, etc., which all 
contribute to wide variability upward. 
These factors in turn lead to mean 
diameters containing large probable 
errors, so much so that when a series 
of them in consecutive size classes is 
compared, a great lack of harmony is 
always found, the amount depending 
chiefly upon the number of tree 
measurements used as a basis. 
HARMONIZING THE CURVES—BAR- 
ROWS^ METHOD 
Having examined the shortcomings 
of the original data, the next step is 
to see how the method of compilation 
.gets around them. 
but may vary from the exact even 
inch; although, as already pointed out, 
this is unusual, except where only a 
small number of trees are measured. 
Average height may also, and very fre¬ 
quently does, fall on one side or another 
of the exact middle point of the height 
class as shown in Figure 1. Nowhere 
does Barrows intimate that this occurs, 
although he particularly points out the 
more infrequent case of the average 
tree failing to fall on the even inch of 
the proper d. b. h. class. 
One fact that helps to prevent the 
errors in the upper parts of taper curves 
from becoming extremely serious is the 
stability of the end point derived from 
averaging the total heights of the trees. 
Tig. 1— Difference between mid values in various height classes and actual average values due to asym¬ 
metrical distribution of values 
The conventional method of Barrows 
consists of several series of curves, of 
three primary forms shown in Figure 2 
in a somewhat simplified form, conical 
trees and straight lines being used to 
;show more clearly certain points. 
The first series of curves, exemplified 
in Figure 2, A, is drawn through points 
representing the average diameters at 
different heights, as compiled from the 
original tree measurement sheets. All 
trees of various diameter classes are 
thrown into one chart, a separate chart 
being made for each height class. 
Drawing curves through the plotted 
points serves to iron out minor irregu¬ 
larities of form and makes the average 
tree a smooth curve. These curves do 
not necessarily pass through the exact 
middle value of each d. b. h. class, 
At the same time the possibility of 
errors in the higher parts of all curves 
presents a considerable problem. Such 
errors all contribute to irregularities 
and peculiarities of shape in individual 
curves which can only be properly 
straightened out by an efficient method 
of harmonization. 
Figure 2, A, shows the first series of 
curves simply by the use of straight 
lines. Accepting Barrows’ statement, 
they are shown failing to pass through 
the middle value in each inch class (the 
even inch) at breast height, but at 
present for simplicity’s sake are as¬ 
sumed to converge exactly at the 70- 
foot point. 
The second series of curves is shown 
in Figure 2, B. In this series of curves 
the d. b. h. of the tree is made the 
