APPENDIX ADEQUACY OF DATA 



659 



arising from destructive events if these events 

 were stabilized each year at the 1952 level. Thus, 

 to the extent that 1952 was an average year for 

 destructive events the growth losses presented 

 are estimates of average annual losses. The two 

 parts of growth loss, as explained in the section 

 Forest Protection, are growth deficiency and loss 

 of accumulated growth. Calculations of growth 

 deficiency were made in several ways: For ex- 

 ample, if a 1952 fire caused an estimated 5-year 

 delay in restocking on a 500-acre recently cut area 

 because the seed source was eliminated by the 

 fire, and if the average per acre volume at 50-year 

 rotation age is judged to be 20 thousand board- 

 feet per acre, then: 



Growth loss= ^^^"^^^'"^ft^ X20 M bd.-ft.X500 acres = 

 50-year rotation 



1,000 M bd.-ft. 



Or if a 1952 defoliation due to a sawfly affected 

 100 acres of pine timber and 800 acres of pine 

 plantations by reducing the growth 60 percent 

 and 30 percent, respectively, and if the average 

 annual growth was 60 cubic feet per acre, then: 



Growth loss (timber) = 



100 acres X 60 cu. ft. X60 percent = 3, 600 cu. ft. 



Growth loss (plantation) = 



800 acres X 60 cu. ft. X30 percent =14, 400 cu. ft. 



Total growth loss = 18,000 cu. ft. 



Losses due to heart rots were computed sepa- 

 rately for merchantable and cull trees. In mer- 

 chantable trees, they represent an average annual 

 rot increment — not for the events that happened 

 in 1952 but for the average situation found in 1952. 

 This obviously includes an accumulation of results 

 attributable to many previous happenings. How- 

 ever, this rot increment is not going to stop as 

 long as infected sawtimber and growing stock are 

 present. Hence, it was felt that the annual loss 

 computed in this way comes close to approximat- 

 ing future annual losses. The loss due to heart 

 rot in cull trees is equivalent to their annual gross 

 growth because no net growth is produced on 

 trees entirely unmerchantable. 



Site deterioration also may result in growth 

 deficiency. For example, fire may damage the 

 soil and change the environment on 1 ,000 acres so 

 that instead of a ponderosa pine forest, a stand of 

 oak, brush, and scattered pine is likely to occupy 

 the site. If annual growth before the fire had 

 been 250 board-feet per acre and only 50 board- 

 feet with the stocking and type of stand after- 

 wards, then a growth loss of (250 board-feet— 50 

 board-feet) X 1 ,000 acres, or 200 thousand board- 

 feet, occurs. 



Calculation of the loss of accumulated growth 

 was handled in the same general manner as growth 

 deficiency. If fire killed 100 acres of 10-year-old 



trees below 5.0 inches in diameter, and if the 

 average per acre yield at a rotation age of 120 

 years is judged to be 72 thousand board-feet, then: 



Growth loss= ,-„ 10 years ^^^ ^ bd.-ft. X 



120-year rotation 



100 acres = 600 M bd.-ft 



Reliability of Estimates Rests on 

 Extensive Body of Data 



The growth impact estimates are based on an 

 extensive body of data from permanent sample 

 plots, special surveys and research studies. Forest 

 Survey measurements, standard fire reports, and 

 a variety of other sources. Such records were 

 used first and were supplemented by professional 

 judgment only when no other basis was available. 

 vSampling errors enter into some of these source 

 data, but there is no way of calculating a sampling 

 error that would apply to the total estimate of 

 growth impact. 



The most significant possibility of error lies in 

 the exercise of professional judgment. There 

 were numerous instances, as the above brief de- 

 scription of procedures shows, where such judg- 

 ment had to be applied. However, the chances 

 of error from this source were reduced as much as 

 possible by intensive crosschecking and wide- 

 spread review and by limiting the use of judgment 

 to those instances where sufficient data did not 

 exist. 



Among the different kinds of mortality and 

 growth loss data, fire data were the most complete. 

 Numerous standard fire reports were available; 

 these ordinarily show timber losses. For severe 

 fires, special surveys are often made to evaluate 

 damage. Delays in restocking and other indirect 

 losses caused by fire were judged but with many 

 .previous situations to use as references and guides. 

 The fire statistics on area protected, classes of 

 protection, area burned, and control expenditures 

 are of a high order of reliability; such statistics 

 have been developed over the years as an essential 

 phase of the integrated State and Federal fire 

 control program. 



The estimates of damage from insects and dis- 

 eases were largely prepared by the entomologists 

 and pathologists located at the Federal forest ex- 

 periment stations. The estimates were derived in 

 part from current surveys, as in the cases of many 

 of the bark beetles, defoliators, white pine blister 

 rust, and pole blight; in part from estimates based 

 on a large amount of data on cidl percents as in 

 the case of heart rot; and in part from scattered 

 studies and the considered opinion of those special- 

 ists who were best informed. Some of the esti- 

 mates in this last category are those pertaining to 

 tip moths, sawflies, leaf and needle diseases, and 

 sweetgum blight. Cull percents used in calculat- 

 ing heart rot losses were based on a substantial 

 body of data, and suitable allowances and weight- 



