186 



TIMBER RESOURCES FOR AMERICA'S FUTURE 



the average annual losses arising from destructive 

 events if these stabilized each year at the 1952 

 level of such events.*" It was not always possible 

 to isolate the damage caused by 1952 attacks of 

 some diseases such as root and heart rots, and 

 many insects. In these cases, mean annual loss 

 is used to represent the loss due to the damage 

 occurring in 1952. 



The timber losses due to catastrophic events, 

 discussed later, are not included in any of the 

 growth impact figures. These losses result from 

 highly unpredictable events that are characterized 

 by extremely severe and concentrated damage. 



Growth impact data do not include the efi^ects 

 of destructive agencies on the quality of timber. 

 It is known, for example, that roundheaded borers 

 and carpenter worms severely impair the quality 

 of oak in the southern hardwood region and else- 

 where. The roundheaded borers, flatheaded 

 borers, and other insects not positively identified 

 cause degrade without killing trees or reducing 

 growth. Other insects and fungi also damage 

 saw logs, pulpwood, and other cut products while 

 still in the woods or while in storage at the mill. 

 Although these losses all have an impact on the 

 timber situation, evaluation of the extent of loss 

 is beyond the scope of this report. 



Interrelations of Causal Agencies 



In some instances, mortality or growth losses 

 are obviously due to a single cause. For example, 

 a crown fire might wipe out a merchantable stand 

 or kill young trees in a plantation. More often, 

 however, losses may be due to a combination of 

 causes. Therefore, in considering the relative im- 

 portance of the several destructive agencies, the 

 reader must keep in mind that their effects are 

 interrelated. This interrelationship is particularly 

 significant when the possibilities for control are 

 being evaluated. For instance, reduction of butt 

 rot losses in Appalachian hardwoods might best 

 be achieved through improved fire control, which 

 would cut down the number of basal fire wounds 

 through which deca}^ organisms gain access. 



In this report, losses are assigned to the causal 

 agency most directly responsible. For example, one 

 of the m.ore important losses is from heart rots. 

 Much of this rot enters through basal fire wounds, 

 some through tops and branches broken by wind, 

 snow, or ice, and some through basal logging 

 wounds. There is some information for the South 

 from which the proportion of heart rot due to fire 

 wounding could be determined. Even there, how- 

 ever, little information exists for assigning other 



<" For method.s used in determining growth impact, 

 including sample calculations of (1) growth loss due to 

 delays in restocking, reduction in vigor, heart rots, and 

 site deterioration, and (2) loss of accumulated growth and 

 adequacy of estimates of growth impact, see Adequacy of 

 Data, appendix, p. 649. 



heart rot losses to weather, logging damage, or 

 similar som-ces. Hence, the entire loss from heart 

 rots was attributed to disease as the direct cause, 

 rather than to the four or more causes initially 

 responsible for entry of the heart rots. 



There are many interrelations. Fire often 

 stimulates insect outbreaks by weakening timber, 

 thus providing breeding places for insects. The 

 Tillamook burn and the Bandon fires in Oregon 

 were followed by major Douglas-fir beetle out- 

 breaks in green timber adjacent to these burns. 

 In turn, insect outbreaks are frequently followed 

 by damaging fires because of the extensive areas 

 of flammable fuels created by the insect attacks. 

 Insects are sometimes the carriers of tree diseases, 

 as in the cases of the Dutch elm disease and the elm 

 phloem necrosis. At other times, insects follow 

 behind disease to complete the destruction. 



As alread}?^ mentioned, windfalls frequently 

 provide a favorable breeding place for insects that 

 emerge and attack surrounding healthy timber. 

 Hundreds of square miles of forests and 5 billion 

 board-feet of Engelmann spruce and lodgepole 

 pine were killed in western Colorado between 

 1940 and 1951 from an outbreak of Engelmann 

 spruce beetle which generated in a windfall of 1939. 

 The western pine beetle, southern pine beetle, and 

 birch dieback in the A^ortheast are definitely 

 favored by drought. Lightning-struck pines are 

 frequently attacked b}' bark beetles, and lightning- 

 struck oaks in P*ennsylvania hav^e become oak 

 wilt centers. 



Many other similar examples of interrelations 

 could be cited. The complexit,y and the manner in 

 which causal agencies often work together preclude 

 any other satisfactory system of loss classification 

 than assigimient of loss to the agency most ; 

 directly responsible. 



Forest Protection as Analyzed 

 IN Past National Appraisals 



In the past 25 years, tlu-ee nationwide timber 

 appraisals have been made, and reports were pub- 

 lished in 1933, 1941, and 1946. Each of these re- 

 ports stressed that protection of forests from fire, 

 insects, disease, and other destructive agencies is 

 necessary if we expect to get full timber produc- 

 tion from our forest lands. Each presented sta- 

 tistics to show the magnitude of the losses from 

 the major causes of timber destruction, as an 

 indication of the size of the protection problem. 



In all of the previous nationwide appraisals, es- 

 timates of timber drain from fu-e, insects, and 

 disease were confined to the cubic feet, board-feet, 

 and cords of timber actually destroyed. They 

 did not include the amount of loss in current 

 growth from insects and disease or the impact of 

 these agencies on future growth, although these 

 effects were recognized as important. Because 

 this report presents separate data for impact from 



