282 METHODS OF TIMBER ESTIMATING 



base line is a primary feature of the forest survey. Where a land survey 

 exists which is accurate and easily traced, or where such a survey is 

 retraced, it may serve as a base line. 



Where the area is small, and a survey and map exists, the corners 

 and known or located points on the boundaries of the tract are sub- 

 stituted for a base line as points from which to initiate strip surveys. 

 The same rules apply as to the necessity of tying in each strip on its 

 completion to some known point on the map, in order to check errors 

 in the survey which would affect the areas determined. 



In running the strip, the estimator is dependent upon the compass- 

 man for the distances from which the areas are determined and the 

 estimate separated by 40-acre tracts. Errors in measuring this dis- 

 tance will cause the cruiser to misplace timber, thus altering the accuracy 

 of the individual estimates per forty. Where types or differences in 

 stand are separated in estimating, the distance across each separate 

 type, as kept by the compassman, will determine the area and con- 

 sequently the accuracy of the estimate within the type. If errors are 

 incurred, their character and extent is revealed by tying in to known 

 points, which enables the construction of a correct map and the correc- 

 tion of the estimates. 



In running estimates over separate forties, it is customary to run 

 strips 1 mile in length, cruising a tier of 4 forties before returning. 

 Where one strip per forty is run, the estimate for the forty is completed 

 at the end of 80 rods. Where two or more strips are run per forty, 

 the tally of the timber on each forty is separated for each strip as indi- 

 .cated to the cruiser by the compassman, and is not completed until 

 the last strip on each forty is run. The results for each strip on the 

 same forty are usually tallied together on the same sheet, and care 

 must be exercised not to misplace or mix up these tallies. 



223. Systems of Strip Estimating in Use. Examples of systems of 

 estimating in which the various factors itemized above are harmonized 

 to meet a given set of conditions, are given below: 



Forest Service Standard Valtiation Survey. This system was used almost uni- 

 versally by the Forest Service and with minor modifications is still a standard method 

 used on national forests. Its characteristics are: 



Width of strip 4 rods or 1 chain 



Number of strips per forty 1 to 2 



Per cent of area estimated, 5 to 10 



Measurement of distances By chain or tape 



Measurement of trees, diameters By calipers or Biltmore stick or ocular 



Heights Sample heights by hypsometer 



Forest types Separated and coordinated with a\ciaj.,c 



heights 



Cull factor Estimated by a total per cent 



Corrections from strip estimate for 

 average stand None 



