Errors in Estimating Timber. 171 



There are a number of interesting points' in the above table 

 worthy of note. It will be noticed, for example, that in many 

 instances the 5 per cent, estimate gave better results than the 10 

 per cent, estimate. This is to be expected since the 10 per cent, 

 estimate is the total of the two 5 per cent, strips, and the error 

 is half way between the errors involved in the 5 per cent, esti- 

 mates. It also shows that a particular cruise line often happens 

 to pass through a stand more typical of the entire area than is 

 represented by the average of the two strips. On the other hand, 

 the maximum error, as might be expected, is very much greater 

 in the 5 per cent, than in the 10 per cent, cruise. Thus, while 

 the greatest error by the 10 per cent, method, considering only 

 the totals, is minus 12 per cent, in Lot C, the greatest error in 

 the 5 per cent, estimate is minus 31 per cent in Lot A. 



The totals for individual lots show greater error than the 

 total for the entire section, the greater errors' being respectively 

 minus 31 per cent, and minus 10 per cent, in the 5 per cent, cruise, 

 and minus 12 per cent, and minus 6 per cent, in the 10 per cent, 

 cruise. 



The individual species, especially on the separate lots, show the 

 greatest error, which in one case amounts to over 100 per cent. 

 When the totals for the entire section are considered, the great- 

 est per cent, of error is plus 40 for sugar pine in the 5 per cent, 

 estimate and minus 30 for incense cedar in the 10 per cent, 

 cruise. 



Ths Yosemite Are;a. 



The check-cruise on the Yosemite tract covered an area of 

 1,560 acres, located at an elevation varying from about 4,000 to 

 6,800 feet. The forest consists of a fine stand of timber averag- 

 ing over 46,000 feet per acre. The species in mixtures are yel- 

 low pine 37%, sugar pine 32%, fir 19% and cedar 12%. The 

 topography is quite level and all exposures are represented. The 

 usual types are yellow pine and sugar pine. There were 35,529 

 trees, 12 inches and over in diameter, on the area measured, or 

 an average of 22.8 trees per acre. Of this number, 491 trees or 

 an average of .3 trees per acre were more than 60 inches in 

 diameter. 



The original estimate was made by a crew consisting of nine 

 men, four of whom had had previous reconnaissance exper- 



