Appendix 



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Forest Survey Procedure 



AN INVENTORY of the Indiana forests was 

 ^ made during the period of November 1949 to 

 December 1950. The sampling procedure used 

 included an office study of aerial photographs and a 

 field examination of forest and nonforest plots selected 

 at random. 



Area Estimates 



The amount of forest land was computed by placing 

 a transparent sheet marked with uniformly spaced 

 dots over aerial photographs and counting the dots 

 falling on forest and nonforest areas. The percentage 

 of forest dots in a county, multiplied by the total 

 county area, gave a preliminary estimate of the forest 

 area. This figure was later adjusted after field 

 examination of selected plots showed how many of 

 them had changed from forest to nonforest and vice 

 versa since the date of aerial photography. 



Systematically selected dots falling on forest land 

 were marked on the photographs. The acre sur- 

 rounding each marked dot was examined stereoscopi- 

 cally and classified by stand-size class according to 

 height, crown width, and number of trees on the plot. 



Plots to be examined in the field were randomly 

 drawn but the selection was weighted — more of the 

 larger stand-size classes were selected than the smaller. 

 Crews of two men located these points on the ground 

 and established a Js-acre circular plot at each point. 

 Such data as tree species, size, log quality, cull, and 

 growth of trees were recorded (fig. 37). 



The following tabulation shows the number of dots 

 and plots examined for the State. 



Photo dots counted for forest-area determLnation . ... 195, 941 



Plots stereoscopically examined on photos 9, 700 



Forest plots field examined . .'. 1, 789 



Nonforest plots field examined 292 



Volume Estimates 



Sawtimber volume. — The gross board-foot and 

 cubic-foot volume tables used in the Indiana Forest 



Figure 37. — Field crew taking sampte tree measurements on a plot in 

 Indiana. 



Sur\-ey were based on the Mesavage-Girard form 

 class tables (6). A\erage form classes were computed 

 from measurements of form class on 1,173 trees for 

 12-, 14-, and 16-inch and larger diameter groups. 



The upper stem \olume of all sawtimber trees was 

 computed between the merchantable top and a point 

 on the central stem with a minimum top 4.0 inches in 

 diameter inside bark. 



PoLETiMBER VOLUME. — Diameter and merchantable ! 

 height were measured on 1,018 poletimber trees in ihc 

 State. These measurements were summarized b\- 

 species group, merchantable height, and by d. b. h. ■ 

 Cubic-foot volume tables were prepared using the 

 volumes computed in other States for trees haxint; ihc 

 same height and diameter relationships. 



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Forest Resource Report No. 10, U. S. Department of Agriculture 



