120 OUR FORESTS AND WOODLANDS 
vary from about two to ten thousand cubic feet 
(true contents, not reduced by square-of-quarter- 
girth calculation) per acre, according as the wood 
may be a thin crop on inferior soil, felled at 
120 years of age, or a full crop on very good 
soil, harvested at 160 years of age. 
In felling mature oak trees in Britain it is 
usual to bark them first of all; and this can 
only be done during the spring, when the sap 
is in most active flow. While the price of oak- 
bark stood high—and formerly it commanded a 
good sale—the harvesting of this was an im- 
portant operation in British woods, and even 
in the hedgerows where oak grew. This was 
another very good reason, in addition to 
the desire for curved timber for shipbuilding, 
for giving each tree a free space for growth 
and lateral expansion, as in hedgerows and 
copsewoods, because the number of branches 
increased the total quantity of bark, besides 
making it thick and rich in tanning properties. 
But the market has now fallen so much that 
it is often questionable if the advantage obtain- 
able from the sale of the bark really compensates 
for obvious drawbacks attendant on the felling 
