Appendix 



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^^ 



How the Suri'ey Wiis Made 



THE resource data presented in this report are 

 based upon an initial field inventory made 

 in the years 1934-36, corrected and brought 

 up to date as oi January 1950. 



The original timber inventory (1934-36) was a 

 line-plot cruise in which lines were rim east and west 

 at 10-miie intervals, and filth-acre sample plots Avcre 

 measined every one-eighth inile throughoiu the 

 forest and woodland sections of each State. The 

 type of forest cover, size class, and density of stand 

 were recorded and trees were measured to get aver- 

 age volumes per acre. This gave a basis for estimat- 

 ing the area of land covered by forests of different 

 kinds as well as the vokmie of timber thereon (<^). 

 The statistics were revised by bookkeeping methods 

 in 1945. 



Beginning in the fall of 1946, the experiment 

 station, with cooperation of the States and other 

 landowners, made a resurvey of a nimrber of coun- 

 ties and parts of counties. Up-to-date figines on 

 areas, voliunes, growth, and allowable cut from 

 these areas were used as background information 

 and as a further means for bringing regional esti- 

 mates to a current basis. 



Cinrent annual growth was estimated on the 

 original siu~vey by use of specially constructed yield 

 tables, discounted for understocked stands. Allow- 

 ance was nrade for the fac t that trees in imder- 

 stocked forests grow faster than trees of the same 

 species and age in the dense forest. Average 

 mortality from fire, insects, diseases, etc., was esti- 

 mated from records of previous losses, reduced 

 where killed material was salvaged. Suppression 

 losses were computed from yield tables and honi 

 records of permanent sample plots manitained Ijy 

 the experiment station. More recent growth esti- 

 mates have been made by a stand projection method 

 utilizing borings and mortality data collected on 

 sample plots, thus providing a check on the results 

 from yield tables. 



As a basis for commodity drain, a virtually com- 

 plete canvass of wood-using industries Avas made in 

 Minnesota in 1934, Michigan in 1935, and Wiscon- 

 sin in 1937. During the subsequent years, annual 

 or periodic production records were maintained for 



Forest Resources of the Lake States Region 



sawmills, pulp mills, and several other industries. 

 Sampling surveys were made in 1946, 1947, and 

 1948 to obtain estimates of production of fence 

 posts, poles, mine timbers, and nriscellaneous items. 

 Utilization studies were n^ade to assist in converting 

 production figures into drain on standing timber. 



Ownership data have been obtained insofar as 

 possible from records of individual owneis. Ilie 

 public agencies and most of the large timl^erland 

 owners have their own cruises and status records. 

 The station was able to obtain abstracts of most of 

 this information. For farm woods and the in- 

 numerable small timberland tracts, the measine- 

 ments on the sample plots were used as a basis of 

 estimation. 



Accuracy of Estimates.— The original inventory, 

 based upon 15,000 miles of survey line and 120,000 

 fifth-acre sample plots, had a calculated sampling 

 error of about 0.7 percent for forest area and 1.1 

 percent for saw-timber volume. Corresponding er- 

 rors for single States were 1.2 to 1.9 percent. Errors 

 for individual species, of course, were considerably 

 greater. 



The 1945 and 1950 adjustments to calculate vol- 

 umes were based upon estimates of growth and drain 

 during a 10- to 15-year period since the original 

 survey. Each of these elements, adding up to more 

 than one-third of the initial inventory, contained 

 possibilities of rather large errors, but recent data 

 based ujDon revised national-forest. State, and indus- 

 try surveys and the several intensive county surveys 

 made since 1946 were available to strengthen the 

 estimates of area, volume, and ownership. Thus 

 the 1950 estimate of volume, although considerably 

 less accurate than the original estimate, still is a 

 usable figine to portray the over-all situation in the 

 region. 



Co))iuio)i and Botanical Names of 



Pri}icipiil Tree Species 

 Trees Included in the Timber Estimates 



' Recotrnhcd Common Ndinc Bolaiiical Name 



Ash, black Eraxirius nigra Marsh. 



Ash, green F. pennsyliuinica var. 



lanceolata (Borkh.) 



Sarg. 



55 



