62 



TIMBER RESOURCES FOR AMERICAS FUTURE 



years may be the cause of large reductions in 

 growth of sawtimber and growing stock. 



In the Timber Resource Review, nationwide 

 estimates have been developed for the first time 

 for both mortality and this additional loss of 

 growth. 



A new term used to describe this total damage 

 is "growth impact." It consists of two elements, 

 (1) mortality, which simply means loss of trees of 

 measured size through death from natural ce 'ses, 

 and (2) growth loss. 



Growth loss consists of (a) reductions in growth 

 due to reduced tree vigor, increase in amount of 

 cull, site deterioration, defoliation, or any other 

 factors reducing growth; (b) losses in growth as a 

 result of delays or deficiencies in stocking resulting 

 from a destructive agent; and (c) losses in growth 

 and prospective 3delds due to the killing of trees 

 below measured size. Thus growth impact, as 

 used in the Timber Resource Review, consists of 

 mortality in 1952 plus the growth losses in 1952 

 and subsequent j^ears resulting from 1952 events. 

 Growth impact represents the annual loss in 

 growth to the extent that destructive events of 

 each year are stabilized at the 1952 level of such 

 events. Growth impact, a new term for some- 

 thing that has long been recognized, is discussed 

 more completely in the section "Forest Protec- 

 tion." It is believed to be a more sound and 

 realistic indicator of the true effect of destructive 

 agents than is mortality alone. 



Growth impact considers only losses in volume. 

 Additional losses in quality are known to take 

 place, but were not evaluated. Comparisons of 

 mortality and growth impact as subsequently 

 presented show that the latter may exceed 

 mortality three to four times. This means that 

 traditional concepts as to the significance of 

 destructive agents will need to be adjusted upward. 



Frequently growth impact on a given stand of 

 timber results from the activity of two or more 

 destructive agents. For example, in eastern hard- 

 woods, heart rot fungi gain access most often 

 through basal fire wounds, but they also attack 

 through logging wounds and broken limbs result- 

 ing from wind or ice storms. Lightning-struck 

 trees may be attacked bj'' bark beetles which may 

 spread to nearby trees. Often the last of two 

 destructive events obscures effects of the earlier 

 one. There are many such examples. 



The complexity of such interrelations and the 

 current lack of information on the initial cause of 

 damage in many cases precludes the possibility of 

 so assigning loss. Thus, where two or more de- 

 structive agents may have been involved, losses 

 have been assigned to the most immediate or direct 

 cause. For example, growth impact due to heart 

 rot in eastern hardwoods has been attributed to 

 disease rather than partly to fire, partl}^ to 



weather, and partly to logging wounds. Losses 

 resulting from fires that started in the heavy ac- 

 cumulation of fuels resulting from a blowdown 

 have been attributed to fire rather than weather. 

 Estimates of damage from destructive agents in 

 the Timber Resource Review are not comparable 

 to damage estimates made in the 1945 and earlier 

 appraisals of the timber situation for two reasons : 



(1) The Timber Resource Review includes both 

 epidemic and endemic mortality from in- 

 sects and disease, whereas earlier appraisals 

 included only estimates of epidemic timber 

 mortality not salvaged. As a result, mor- 

 tality in the Timber Resource Review is 

 more than three times that of earlier esti- 

 mates. 



(2) Estimates of growth impact have been de- 

 veloped. This has not been done before on 

 a national scale. In cubic feet, the growth 

 impact from destructive agents other than 

 fire is more than nine times that of the 

 mortality loss given in the 1945 Reappraisal. 

 Failure to understand these differences 

 might lead to the erroneous conclusion that 

 little progress has been made in controlling 

 many of the more serious insect and disease 

 epidemics. Such a conclusion would not be 

 justified. 



In addition to the insect, disease, fire, and other 

 losses that form the basis for the mortality and 

 growth impact estimates in the Timber Resource 

 Review, there are the so-called "catastrophic" 

 losses, which are of extraordinary severity and so 

 unusual as to be unpredictable as to location or 

 frequency. These losses are discussed separately 

 and are one of the major reasons why a margin is 

 included in the estimates of the growth needed to 

 meet projected timber demand. 



Destructive Agents Take Extraordinary 

 Toll 



As noted earlier, mortality of sawtimber in 1952 

 as the result of damage by fire, disease, insects, 

 weather, and other factors, was 12.7 billion board- 

 feet. Adding to this a growth loss of 31.1 billion 

 board-feet means that growth impact of 43.8 

 billion board-feet was nearly four times mortality 

 (table 39). These estimates, however, represent 

 total losses without allowance for the amoimt of 

 dead timber that was utilized. Salvage amounted 

 to about 770 million cubic feet of growing stock 

 including over 3 billion board-feet of sawtimber. 

 Thus, for sawtimber, there was a net loss due to 

 mortality of 9.6 billion board-feet, and of 40.7 

 billion board-feet due to growth impact. In terms 

 of growdng stock, the net losses were 2.7 billion 



