TRAINING REQUIRED TO PRODUCE TIMBER CRUISERS 307 



discontinued and a total count substituted with a tally of one tree in three. The 

 area is increased to 60 acres per day. It is the universal testimony of cruisers 

 that this simplification of the tally relieves the mind of a strain and improves the 

 accuracy of the dimensions talUed and consequently of the total estimate. It has 

 been found that an average volume is obtained through a tally of one-third of the 

 stand under the following conditions : 



When there are at least 500 trees per 40 acres of the species tallied and preferably 

 1000. 



When the judgment or process of selection is entirely eliminated in favor of 

 mechanical selection of the trees to be tallied. This may be done by taking every 

 third tree in succession or bj' taking the nearest tree in each case. Where there are 

 insufficient trees to insure the mechanical average, or where the range of size is large, 

 the count may be separated into two groups, segregating the large from the small 

 trees, one tree in three tallied separately in each group. This adds very little to 

 the detail required when working with a single species. 



5. Only 50 per cent of the area is estimated by the above method. The area per 

 day is nominally 120 acres. The remaining area is inspected by eye at distance of 

 20, 40 and 60 rods in order to apply a weighted 



volume correction factor as described in § 229. 

 In this method, four strips are run, each 10 rods 

 wide, as before, starting from points, 5, 25, 45, 

 and 65 rods from the corner and alternating 

 with strips not estimated as per Fig. 63. 



In order to check the correction factor, the 

 alternate strips not previously estimated are now 

 in turn estimated, keeping the record separate 

 from the original four strips. The correction 

 factor derived from observation is first com- 

 puted and the corrected estimate is then com 

 pared with the tally of the strips estimated. 



6. Up to this time no effort has been made 

 to deduct for cull which would introduce an 

 arbitrary factor interfering with the comparison 

 of the work of the cruiser with the measurement 

 of the plot, both of which have been on basis 

 of sound contents, disregarding possible cull. 



The cull factor is now tested by close examination of 10 acres in which every tree 

 is individually estimated and the per cent of probable cull recorded and subtracted 

 from the estimate. Per cent figures also are obtained from the scale of logs of 

 similar timber in the vicinity and these per cents are used as a basis of cruising. 



7. In actual cruising, the per cent of area covered is reduced to 25. The area 

 is increased to 320 acres per day, and 4 miles of line run. A cull factor is used and 

 hardwoods are added to the estimate by tallying the top diameter of each mer- 

 chantable log, inside the bark. 



8. The cruiser is then brought back to the sample plots to receive training in 

 individual estimating. This consists of: 



The use of circular plots covering different per cents of the area by a systematic 

 plot method and finally by the selection of a sample plot by eye. On these plots, 

 he first arrives at the volume of the average tree either by direct approximation or 

 by selection of a tjT^ical tree whose volume is ascertained from a volume table; 



A tally of the diameter and height of each tree on the plot and the immediate' 

 computation of the volume to ascertain the true average tree for comparison with 



Fig. 63. — Method of estimating a 

 forty by use of the correction 

 factor. Points at which obser- 

 vations are taken shown by 

 dots. 



