1/4 Forestry Quarterly. 



under consideration, while column seven shows the same for the 

 individual species in each tract. 



The last two columns in the table are the true measure of the 

 relative accuracy of the 5 per cent, and the 10 per cent, estimates. 

 It will be seen that when the entire area of 1560 acres is con- 

 sidered the 10 per cent, estimate cuts down the maximum error 

 by 5 or 6 per cent., but when individual "forties" are considered 

 the difference in the greatest error between the 5 per cent and 

 the 10 per cent, cruise amounts to 33 per cent., if only the total 

 estimate is considered, and to 68 per cent., if the individual 

 species' are taken into consideration. 



The table brings out very clearly the danger of giving out de- 

 tailed estimates by small areas when only a comparatively small 

 per cent, of the area has been estimated. It shows, for example, 

 that when a 5 per cent, cruise is made and the error is as high 

 as 71 per cent, on an individual "forty" it drops to a maximum 

 of only II per cent, on 1,560 acres. In a 10 per cent, cruise the 

 greatest error drops from 38 per cent, to 5 per cent. When in- 

 dividual species are taken into consideration the increase in ac- 

 curacy by lumping the estimates is still more apparent. 



The inaccuracy of the estimate on individual "forties" in the 

 Yosemite tract was no doubt increased by the occurrence of a 

 few very large sugar pines from 70 to over 100 inches in diameter. 

 It stands to reason that where these large trees occur sparingly 

 on a "forty" and the cruise strip happens to strike one or more 

 of them the estimate will be too high; if it misses them the 

 estimate will be too low. In either case the error will be large 

 unless there is a sufficient number of these big trees to allow of 

 a uniform distribution. 



It should be borne in mind that the object of the discussion 

 is to show the relative accuracy of a 5 per cent, and a 10 per 

 cent, cruise, and that we are therefore not concerned with the 

 actual errors made. It must be remembered also that Table 3 

 gives the greatest errors and is no indication of the actual ac- 

 curacy obtained by the original cruise. 



Since most of the government timber on the National Forests 

 is sold by actual scale, and not by estimate, it would seem that 

 a very careful cruise is not required. However, since the stump- 

 age price charged will depend to some extent on the amount of 



