Figure 8. — Longleaj pine stand immediately after thinning, Clay County, Fla. 



sustained-yield possibilities of the tributary terri- 

 tory, since only thus can assurance be given that it 

 will be a permanent installation and a genuine 

 benefit. 



Forest Increment 



Individual trees increase in volume from year to 

 year through growth in diameter and height, 

 provided that they are sound and that any loss of 

 volume due to rot, turpentining, or other damage 

 does not offset growth. Timber stands, made up of 

 many thousands of individual trees, likewise show 

 an increase in volume if the aggregate net growth of 

 the constituent trees more than offsets the constant 

 attrition caused by fire, windthrow, turpentining, 

 natural crowding out, and other causes of tree 

 mortality. Such increases or decreases in tree and 

 stand volume constitute a plus or minus increment. 

 The volume growth of an individual tree can be 

 accurately measured, but computation of incre- 

 ment, even for a year, of a forest area of several 

 million acres, involving as it does many complicat- 

 ing factors of species, density of stand, forest condi- 

 tion, site, weather and the presence or absence of 

 unfavorable utilization practices, cannot be precise. 



PERIODIC ANNUAL INCREMENT 



It is estimated that trees are harvested each year 

 from less than 250,000 acres of forest land in north- 

 eastern Florida. The remainder is unaffected by 

 utilization practices during any one year, and forest- 

 land owners are, therefore, interested in the rate at 

 which these forest stands are increasing in volume. 



The increment percent — that is, the rate at which 

 timber bodies increase in volume — is principally 

 affected by the forest condition and by the rates of 

 growth and mortality of the species making up the 

 stand. The percents shown in table 18 can be used 

 in approximating increment of the several species 

 groups in average stands of the various forest condi- 

 tions shown, provided that the area considered is 

 large enough to smooth out the extremes of site, 

 density of stand, and effects of utilization. 2 The 

 board-foot increment rates include both the in- 

 crease in volume of trees already of saw-timber size 

 and the volume in trees that reach saw-timber size 

 during the year. The cordwood rates include the 

 increase in volume of all trees 5 inches and larger 



2 Note that these rates must be compounded for the period 

 over which the user desires to compute increment. 



32 



