VIRGINIA FOREST RESOURCES AND INDUSTRIES 
Forest Increment and Commodity Drain | 
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and kinds of timber in the State and the industries 
and enterprises dependent on this raw material. 
These facts by themselves, however, do not reveal 
Pirates sections have reported the volumes 
whether the forest capital (growing stock) is being 
expended at an excessive rate or whether growth is 
sufficiently in excess of drain to increase the capital. 
This section of the report sets up a balance sheet of 
growth and drain and evaluates some of the conflict- 
ing trends that make an appraisal of the forest situ- 
ation extremely difficult. 
Forest Increment 
In all calculations of forest increment, three elements 
are factors—gross increment, mortality, and net in- 
crement. Gross increment is the increase in volume 
of the growing stock in saw-timber or cordwood trees 
uncorrected for losses by mortality or deterioration, 
plus the volume in smaller trees reaching the minimum 
diameters for these classes during the year. Mortality 
is the loss due to such causes as fire, wind, insects, 
disease, and suppression, but not from cutting. Net 
increment is the difference between gross increment 
and mortality.’ 
Mortality 
In 1940 the net volume of trees 5.0 inches d. b. h. and 
larger that died during the year amounted to 579,000 
cords. Of this total, 331,000 cords were softwoods 
and 248,000 cords were hardwoods. The softwood 
mortality amounted to 8 percent of gross growth and 
the hardwood to nearly 6 percent. Losses of over one- 
half million cords per year are serious enough in them- 
selves but equally disturbing is the great but unmeas- 
ured mortality of the seedlings and saplings less than 
5 inches in diameter brought about chiefly by forest 
fires. 
In terms of saw timber, mortality amounted to 85 
million board feet, 53 million of softwoods and 32 
million of hardwoods. This was 6 percent of the gross 
“For more detailed definitions of increment and drain, see 
Definitions of Terms Used, in the Appendix, p. 57. 
42 Miscellaneous Publication 681, U. S. Department of Agriculture j 
RS 
growth of softwoods and 4 percent of that of the hard- 
woods. 
It is almost impossible to obtain a quantitative meas- 
ure of mortality by causes because of the difficulty in 
assigning reason for death to individual trees. In ad- 
dition, the number of seedlings and small saplings 
completely destroyed by fire, for example, cannot be 
measured accurately on a State-wide basis without a 
prohibitive amount of field work extending over sev- 
eral years. However, careful observation-of each dead 
tree tallied on the survey plots, distributed throughout 
the State, led to the conclusion that fire, insects, dis- 
ease, and wind, including sleet damage, were the major 
causes of tree mortality in Virginia. Logging, natural 
suppression, and lightning appeared to be less im- 
portant causes. 
Wild fire may not be the leading cause of death of 
trees larger than 5.0 inches d. b. h., but certainly it is 
one of the most important. Not only does it kill out- 
F—441810 
Ficure 58.—Eight-year-old loblolly pine totally destroyed by 
spring fire, 1946. ; 
