PRACTICE OF TIMBER ESTIMATING 
197 
constructed on principles that have very seldom been 
employed elsewhere. After basal diameter, taper per 
32-foot 1 log is the next factor allowed for, total height of 
the tree is disregarded, and number of logs is the third 
factor in the tabulation. This has reason behind it as 
well as experience. In timber of such dimensions total 
height is not readily estimated; the lower logs of the tree 
are very much the largest and far the best in quality; 
a log more or less in the top, comparatively small in size, 
full of large knots and liable to be broken up in felling, is 
of small account in the estimate anyway. 
In connection with these tables, basal diameter also is 
handled in a peculiar manner. In some tree species thick¬ 
ness of bark is very variable, while the root swelling of 
large trees frequently reaches to the height of a man and 
higher. Diameter therefore is taken as nearly as may be 
where the tree takes on its regular form, considerably 
above breast height as a rule; deduction is made for any 
swelling not thus allowed for, and double the thickness 
of bark as actually found is then subtracted. By this 
means, the wood alone is dealt with, and basal diameter 
is aligned with the general shape of the tree. 
In view of the facts above mentioned it is clear further 
how windfalls furnish the best obtainable assistance to 
the cruiser’s judgment in respect to height and taper, 
also that the diameter tape and Biltmore stick possess 
advantages over the caliper. Then two additional prob¬ 
lems arising out of the size of the trees confront the cruiser: 
first, breakage in felling is a much more important factor 
than elsewhere, and its amount varies widely with the 
ground conditions; second, the defect arising from decay 
and other sources, very hard to judge, to detect even, in 
timber of this height, has to be handled with extreme 
care — careful looking, the examination of windfalls, 
experience, perhaps the outturn of adjacent timber serv¬ 
ing as a guide to it. 
The “forty” is the ordinary unit of area for cruising 
and a timber report, and it is gridironed with straight 
fine travel. Pacing serves ordinary purposes as a dis- 
1 Tables based on 16-foot logs are also in existence. 
