308 IMPROVING THE ACCURACY OF TIMBER ESTIMATES 



the ocular guess. Two days of this work will greatly improve the ability of the cruiser 

 to substitute ocular methods for measurements. 



An opportunity to run out strip estimates in which he does his own compass work, 

 counting the trees ahead of him in rectangular blocks. The volume of these trees 

 is obtained: 



By the log-run method of estimating the number of logs in the average tree 

 and the average contents of the log or log run per thousand; 



By selecting an average tree in volume for each of eight separate strips, the 

 total tally of which is kept separate. This principle could, after practice, be applied 

 to the entire forty, or to separate groups. 



The exact details of this system as to size of sample plots, widths of strip and 

 methods of tallying heights were worked out for Southern yellow pine, and several 

 of these points would need modification if applied to timber of radically different 

 type and conditions. But the general method of careful, original measurement 

 of the control plots and of proceeding from a 100 per cent intensive estimate 

 through various stages of less intensive work in which the six classes of averages 

 are employed as substitutes for the full tally, can be worked out for any forest 

 type and form the basis of rapid and practical training in the art of timber 

 cruising. 



239. Check Estimating. Just as in the training of a cruiser his 

 greatest drawback is lack of any check on his estimates, so check esti- 

 mating does not benefit the cruiser unless he can be told, not only what 

 the extent of his error is, but just how he made it. Check estimating 

 must depend either upon the infallibility of the check estimator, which 

 may be questioned in the mind of the person checked, or by the sub- 

 stitution of actual measurements on a basis which removes all source 

 of doubt, leaving only cull and quality to be judged. Check estimates 

 should therefore be made on definite areas or- strips, prevously or sub- 

 sequently estimated by the cruiser and on which a record has been kept 

 similar to that indicated in the description of the methods of training 

 timber cruisers. The tree count, the total volume, the average volume 

 per tree, but most important, the tendency to over-estimate heights 

 and diameters should all be checked separately. When this is done, 

 one of two things will happen. Either the cruiser will rapidly acquire 

 a much greater accuracy or he will demonstrate his complete unfitness 

 for the job of timber cruising and can be put on other work. 



240. Superficial or Extensive Estimates. The preliminary examina- 

 tion of a tract of land for the purpose of determining roughly whether 

 it has timber of value and approximately how much, calls for the exercise 

 of the maximum of skill and experience in order to attain a reasonable 

 degree of accuracy in the minimum of time allowed. 



A description of the estimation of a tract of 2300 acres for the Blooming Grove 

 Hunting and Fishing Club, located in Pike County, Pennsylvania, will serve as an 

 illustration of methods possible in such an examination. The field work on Taylor's 

 Creek logging unit occupied two days including travel to and from the unit. Not 

 much over one day was put on the estimate itself. The fundamental basis of the 



