METHODS DEPENDENT ON USE OF PLOTS 297 



with that obtained if the ocular guess in each case were correct. This 

 increases the probability of accuracy in applying the method. Actual 

 tests of this principle have shown that where the average stand per acre 

 off the strip differs as much as from 10 to 15 per cent from that on the 

 the strip, under conditions permitting the inspection or actual seeing 

 of the greater part of the timber, it is possible to reduce the error incurred 

 by the mechanical average by at least one-half, provided the cruisers 

 have some training and skill in application of the principle of ocular 

 estimating. 



230. Methods Dependent on the Use of Plots Arbitrarily Located. 

 In discussing the methods of estimating by means of sample plots, 

 only the systematic or strip method of arrangement has been described. 

 A second plan is to locate these plots arbitrarily by selection based upon 

 individual judgment, the purpose being to get the total estimate by 

 means of a few typical plots and greatly cut down the work required 

 in systematic measurements. As in the strip systems, one of two things 

 is done; either the plots which are measured are taken to represent 

 the average stand per acre for the larger area of which they are a sample, 

 or these plots are merely the basis of arriving at the stand by sub- 

 sequent application of a correction factor. • 



The first plan can be used only in conjunction with the area or type 

 method in order to eliminate, as far as possible, variations in the stand 

 by separating uniform and comparatively small areas. In this case, 

 sample plots selected with care after a thorough inspection may be 

 relied upon within reasonable limits of accuracy. By the second method, 

 the plots chosen are seldom relied upon without further close inspec- 

 tion of the stand. Cruisers using this method employ these plot 

 measurements in order to establish in their minds the volume of typical 

 stands having a definite density and appearance. Once fixed, this 

 standard is used as a basis with which to compare the average stand 

 on the area by exactly the same methods as were described under the 

 correction factor in the strip method. The plots are merely much 

 smaller and have more definite standards than the strips, and their 

 application to the larger area is more difficult. The use of these plots is 

 still further restricted, with improved accuracy, when they are intended 

 merely to determine the volume of the average tree of certain classes 

 of timber, and the estimate on the remaining area is determined by a 

 tree count covering practically 100 per cent. 



Various combinations of the above plans are used, especially in the 

 South, by cruisers working in pine in an effort to cover the ground 

 accurately with a minimum of time and expense. 



231. Estimating the Quality of Standing Timber. An estimate of 

 standing timber is in effect an inventory of raw materials intended 



