270 



Practical Forestry 



The sliding rule is also useful for determining contents. 



The proper allowance to be made for bark is half an inch 

 for every foot of quarter-girth for oak and elm under 12 in. 

 quarter-girth, and an inch for all beyond, but it is quite 

 impossible to fix upon any one uniform scale that will meet 

 even the majority of circumstances. Trees growing in 

 exposed situations will frequently have bark almost double 

 the thickness of those of a similar size in the woodland. 

 My plan has been always to allow for the bark of each tree 

 at the time of measurement. 



Measuring Standing Timber. For this a pliable 

 pole 18 ft. long, marked in feet, and the girt-strap already 

 referred to are the necessary equipment. In estimating 

 the number of feet of timber upon a large area, it is not 

 always necessary to measure each tree separately, particu- 

 larly when the whole situation is composed of one species, 

 and the individual trees are about the same age and size, 

 as by multiplying the total number of trees by the average 

 content of those selected and measured a very just calcula- 

 tion will be arrived at. Great care in their selection, and 

 considerable judgment in taking the average will, however, 

 be required. 



