FIELD APPRAISALS OF TIMBER STUMPAGE 221 



for accuracy are improved in direct ratio to the size of the area 

 units separately measured. Should the figures be desired by 

 separate forty-acre tracts, an estimate covering 10 per cent of 

 the total would leave opportunities for large errors, while for 

 a section of 640 acres, 10 per cent might give quite close results. 

 Large and scattered timber requires a more complete estimate 

 than small trees densely stocked. Very irregular or bunchy 

 stands may require greatly increased work to arrive at a fair 

 result. One method of dealing with this fundamental difficulty 

 is to merely accept the result as within the allowable error for 

 such work. Astonishing errors creep into limber estimates, 

 even with experienced men. 



221. Types. A second plan is to subdivide an area into types 

 by means of a sketch map. In timber estimating, these type 

 divisions are for the purpose of improving the possibility of 

 getting a fair average stand. They are really stand classes. 

 Blank or open areas are mapped and excluded in computing 

 the total estimate. Only the area of strips run within a given 

 type is used in determining the stand on that type. The amount 

 of work which this method entails is somewhat greater than when 

 the timber is calculated on the basis of the whole area, but this 

 is often justified and the plan is used in a rough form by nearly 

 all woodsmen. 



222. Correction Factor. Another method of improving the 

 final estimate without measuring every tree is the correction 

 of the computed total, whenever the observations and judgment 

 of the cruisers indicate its necessity. This correction must be 

 based on actual inspection of the entire body of timber. When 

 running strips, short side trips are made to view the timber which 

 lies outside the strip. Should this timber run heavier or lighter 

 than that measured, the total will be reduced or increased by an 

 estimated per cent. This plan must not be confused with the 

 method of guessing at the total stand, for it is based on a careful 

 estimate, tree by tree, of a portion of the area. Should it be 

 impossible for any reason to actually inspect the remaining 

 timber, there can be no basis for correcting the result, which 

 must stand for what it is worth. 



