274 



METHODS OF TIMBER ESTIMATING 



by topographic blocks and units, rather than by forties or legal sub- 

 divisions, the system of strips will be planned with reference to base 

 lines run along the main bottoms and streams, from which, at regular 

 intervals, the strips will be run directly up the slopes and as nearly 

 parallel to each other as possible. The strips in each separate unit 

 may, therefore, have a different direction. 



220. Factors Determining the Width of Strips. The standard widths 

 of strips used in timber estimating are six in number and their dimen- 

 sions are given in the following table: 



TABLE XLI 

 Relation of Width and Number of Strips to Area Covered 



On rectangular surveys, to compute this per cent of total area 

 covered by the strips, multiply the number of strips run per forty 

 or one-fourth mile square, by the width of the strip in rods, and divide 

 by 80 rods. These two factors, number and width of strips, are not 

 reciprocals since each has a distinct function to perform. The number 

 of strips per forty increases directly the probability of accuracy 

 in securing an average stand or proper sampling of the timber on the 

 area (§ 211). The width of the strip affects this average to a lesser 

 degree. Its principal function is to enable the cruiser to determine 

 accurately the dimensions and volume of the trees which stand upon 

 the strip estimated, and the factors which affect his ability to obtain' 

 this accuracy will determine the width of strip without respect to its 

 effect upon the total area covered. If narrow strips must be run in 

 order to get accurate estimates of timber on the strip, and it is necessary 

 to increase the per cent of area, the number of strips will have to be 

 increased rather than the width of the strip. 



An example of the relations between these two factors is cited by Austin Cary, 

 Manual for Northern Woodsmen, where a system on the Pacific Coast of using two 



