FOREST PROTECTION 



39 



George H. Hepting 

 George M. Jemison 



INTRODUCTION 



A considerable part of the timber volume added 

 annually by growth to forests of the United States 

 is destroyed by fire, insects, disease, animals, and 

 adverse weather. In addition to the timber 

 destroyed, growth is reduced, quality is impaired, 

 land is left understocked, and other damage is 

 sustained from these forest enemies. These 

 losses are great but history shows us that, in 

 addition, occasional catastrophic losses may be 

 compounded upon our relatively normal losses. 

 Therefore, future growth estimates must allow 

 for probable future losses. To the extent that 

 the damage by destructive natural agencies can 

 be reduced, the available supply of timber will be 

 correspondingly increased. 



The purpose of this report is (1) to present and 

 compare the impact of fire, insects, disease, and 

 other destructive events in 1952 on timber growth; 



(2) to describe the types of damage by different 

 destructive agents and their relative importance; 



(3) to analyze the status of efforts to reduce these 

 losses; and (4) to appraise, in general terms, the 

 extent to which losses may be reduced in the 

 future. 



The Basis for Evaluating 

 Timber Destruction 



There are many ways in which destructive 

 agencies affect growth. All of them discussed 

 herein, namely fire, insects, disease, animals, and 

 weather effects, can kill trees. In addition, fires 

 wound trees, laying them open to wood borers 

 and infection by heart rot fungi; or devitalize 

 them, making them prey to bark beetles. Fires 

 are a major cause of understocking and can also 

 deteriorate sites. Such deterioration leads to 

 inferior species composition and reduced growth 

 of the more useful species. 



Besides killing trees, insects and disease cause 

 many other types of damage. They destroy 

 seeds and young seedlings, deform and stunt 

 saplings and poles, reduce growth by killing 

 foliage, and eat out the wood of large trees. 



'" In addition to the tabular data given in this section, 

 more detailed statistics are presented in the appendix, 

 p. 499. 



Animals also cause many types of damage, and 

 everyone is familiar with the destruction resulting 

 from certain caprices of weather — -blowdowns, ice 

 and snow damage, flooding and drought. 



Growth Impact — the Concept and 

 Definition 



In attributing losses and damage to various 

 agencies, a major effort has been made to reflect 

 their full impact on growth as well as to recognize 

 mortality. The preponderance of damage from 

 certain agencies is due to losses in growth rather 

 than mortality. Such is true of the injury caused 

 by the defoliating insects and the heart rots, or 

 the setback in growth from restocking failures or 

 delays following a fire. It is obvious, then, that 

 any real appraisal of damage must include an 

 evaluation of factors causing a reduction in net 

 growth in addition to volume loss through mor- 

 tality. This concept of total growth impact is 

 new in that it has not been used heretofore in 

 national appraisals of the timber situation. 



Mortality and growth loss — ^the key elements of 

 growth impact — are defined as follows: 



Mortality. The volume removed from the 

 total growing stock or the sawtimber portion of 

 it, through death from natural causes, exclusive 

 of catastrophic losses. 



Growth loss. The losses sustained otlier than 

 mortality. It is comprised of the sum of the 

 following two elements: (1) Growth deficiency — 

 the loss due to (a) delay in restocking or de- 

 ficiencies in stocking resulting from a damaging 

 attack or fire, and (b) the reduction in growth due 

 to changes in timber type, defoliation, reduction 

 of tree vigor, increase in cull percent, or deteriora- 

 tion of site; and (2) loss of accumulated growth — 

 the effect on present and prospective yields, of 

 mortality of trees below the sizes measured: in 

 the case of cubic feet of growing stock, below 5 

 inches d. b. h.; in the case of board-feet of saw- 

 timber, below the minimum d. b. h. specified for 

 sawtimber. 



Growth impact. Mortality plus growth loss. 



Although the growth impact figures in this 

 report were computed in various ways depending 

 upon the type of damage, in effect they represent 



185 



