256 ESTIMATION OP STANDING TIMBER 



' (c) The point at which heights are taken — total height o r 

 merchantable log length. 

 (d) The top diameters to which tree must be estimated. Diver- 

 gence in these conditions from those used in the volume 

 table will make it impossible to apply the same. 



5. The local characteristics of the timber to be estimated as to full- 

 ness of form or " form quotient," quality and defects. This determines, 



(a) For sound trees, the applicability of existing volume tables 



without modification or their need of local percentage 

 corrections. 



(b) For the defective trees, the amount of deduction for defects 



and losses in scale to be made from the standard volume 

 table. 



The object of any estimate of standing timber is to obtain the total 

 volume as indicated by the above five conditions upon the entire area 

 of a specific tract of land. This may be done in one of three ways : 



By direct ocular guess or appraisal. 



By actual estimate or measurement of the volume of every tree 



of merchantable size. 

 By measuring or estimating a part of the timber as an average 



of the whole. 



206. Direct Ocular Estimate of Total Volume in Stand. The direct 

 estimation or guess of the total volume of a tract of timber can have 

 but one basis, that of experience in cutting tracts of similar character. 

 This eliminates all doubtful factors, and the experience thus gained 

 is invaluable as a standard of estimating. 



Skill and accuracy in this method depend upon the uniformity of 

 the stand, and the ability of the estimator to compare this uniform 

 stand with those of similar character whose yield he has ascertained. 



As the area of timber so estimated incr ases, its variability of 

 stand becomes greater; yet the necessity for obtaining a true average 

 of these variable conditions persists. Even in stands as large as 40 

 acres it becomes very difficult even with the closest inspection to arrive 

 at the average stand on the tract, no matter how skillful the cruiser is 

 for smaller and more uniform areas. With increasing size of area, 

 accuracy soon becomes utterly impossible. For this reason, in spite 

 of the simplicity of the plan in theory, in practice cruisers who depend 

 solely upon this principle are apt to be unreliable and inaccurate. 

 Under no circumstances can this method be applied to timber with 

 which the cruiser is unfamiliar. It therefore limits his field of activity 

 to a narrow basis. 



