APPENDIX — ADEQUACY OF DATA 



655 



For the purposes of this Review, it was necessary 

 to adjust the area and volume estimates to 

 January 1, 1953, and the net annual growth esti- 

 mates to 1952. In a few States, the Forest Survey 

 data were assembled as early as 1947; in a few 

 other States, part of the data was collected as late 

 as 1954. However, most of the States were 

 covered in between these years and nearly all of 

 the special, less intensive surveys were made in 

 1952 and 1953. Where necessary, adjustments 

 were made for known area changes; timber 

 volumes were adjusted for growth and cutting, 

 and known growth rates were applied to the 

 adjusted volumes to revise the estimates of net 

 annual growth. Usually the time period was short 

 and the adjustments were slight. Overall, the 

 adjustments had only minor effect upon the 

 national totals, but in a few cases they resulted in 

 considerable change in State figures. 



Comparisons With 1945 Estimates 



Indications of changes in forest area, timber 

 volume, and growth cannot be found in compari- 

 sons of the estimates published in various reports 

 on the timber situation in the United States. 

 The reasons for lack of comparability are many 

 and complex; they are discussed in the two 

 sections Forest Land and Timber and Growth and 

 Utilization. Yet trend information is so important 

 that some comparisons are inevitable. In order 

 to make the most valid comparisons possible, 

 some adjustments were necessary. 



Methods varied from region to region, depend- 

 ing chiefly upon the availability of recent Forest 

 Survey data. In most cases, the use made of the 

 original Reappraisal * estimates was limited to 

 area statistics, such as area of forest types and 

 area by stand-size classes. Where the original 

 area estimates could not be used, known changes 

 in commercial forest area, tree mortality rates, tree 

 size distribution, forest type, stand size, and other 

 factors were taken into account in making calcula- 

 tions from more recent surveys. 



In all of the West except the Douglas-fir sub- 

 region, estimates of timber volume in 1945 were 

 derived from 1953 data. This was also true in 

 New England, the Middle Atlantic and Central 

 Regions, and the northern Plains States. In the 

 Douglas-fir subregion and in the Lake, South 

 Atlantic, Southeastern, and West Gulf Regions, 

 new 1945 estimates were obtained by interpolation 

 between the oiiginal Forest Survey (made before 

 1945 in these regions) and resurveys. 



In working back to 1945, the volume estimates 

 were based on the assumption that 1952 rates of 

 growth applied over the interval between 1945 and 



1952, unless there was some evidence to the 

 contrary. The estimates of timber cut used in 

 the volume calculations were large!}' based on 

 Census or other annual output statistics for the 

 major products. Once the 1945 volumes had been 

 recalculated, new estimates of growth were pre- 

 pared by applying 1952 or interpolated growth 

 rates by species to this volume. 



The comparisons with 1945 are admittedly 

 rough, but they are the best that can be made 

 under the circumstances. In addition to the 

 possibility of nonsampling errors, they also contain 

 the sampling errors of the recent data and of earlier 

 data. These sampling errors may be either 

 cumulative or compensating in making the com- 

 parisons. Hence, small changes since 1945 cannot 

 be regarded as significant. 



Estimates for Interior Alaska Are 

 Only Indicative 



All of the estimates of forest land areas in 

 Interior Alaska and of timber volumes, growth, 

 and mortality were made by experienced Alaskan 

 foresters. The estimates were prepared cooper- 

 atively by the Bureau of Land Management and 

 the Forest Service. Such estimates have been 

 prepared from time to time in the past: the present 

 estimates represent a refinement of the older 

 figures, and they incorporate whatever new data 

 were at hand. Chief among the latter were the 

 results of a special study made by H. J. Lutz, 

 entitled Ecological Effects of Forest Fires in the 

 Interior of Alaska, published as U. S. Department 

 of Agriculture Technical Bulletin 1133. Although 

 this bulletin was not published until March 1956, 

 the data contained in it were available in advance 

 to the technicians making the estimates for 

 Interior Alaska. 



Since no complete surveys have been made and 

 since tlie growth studies available are obviously 

 inadequate, it is not possible to attribute great 

 reliability to the estimates here presented. They 

 should be taken as indicative figures only. 



TIMBER UTILIZATION 



The estimates of timber cut in 1952 are suffi- 

 ciently adequate and reliable for national and 

 regional analysis and even for State analysis in 

 many instances. In reliability, many of the utili- 

 zation data compare favorably with ttie data on 

 timber growth. The timber cut estimates depend 

 chiefly upon timber products output or consump- 

 tion * data which have been collected for many 

 years by the Census or the Forest Service. These 



/ 



' U. S. Department of Agriculture, Forest Service. 

 Forests and National Prosperity — A Reappraisal of the 

 Forest Situation in the United States. Misc. Pub. 668, 99 

 pp., illus. 1948. 



" Timber products consumption data appear in the 

 section Future Demand for Timber. They are discussed 

 here because they are closely related to other timber 

 utilization data, and most of them come from the same 

 source as timber products output statistics. 



