Forest Mensuration 27 



If the trees of the forest are defective, the sample trees should exhibit 

 average defects. 



PARAGRAPH XLII. 



FIELD WORK FOR EXACT VALUATION SURVEYS. 



The valuation survey requires : 



1. Calipering of all trees ; the diameter is taken in inches or in multi- 

 ples of inches. Each species and each height class or age class are or 

 may be taken separately. 



2. Entering the takings on tally sheets, arranged as follows : 



The larger the trees are, the bigger is the permissible interval of 

 calipering. If trees average two feet in diameter, an interval of 3 inches 

 is permissible, provided that a large number of trees are calipered. 



It is a strange fact that the diameter measured from east to west is 

 larger on the whole than the diameter from north to south. 



PARAGRAPH XLIII. 



BASAL ASSUMPTIONS. 



The only assumption made in calculating the volume of the forest after 

 Paragraph XLI. is that the form height of the sample trees equals the 

 form height of the forest. No other estimate or assumption is being 

 made. This premise is much safer than the assumption that the volume 

 of the forest bears the same ratio to the volume of the sample trees 

 which the number of trees in the forest bears to the number of the sample 

 trees. More unsafe is the assumption that the volumes of forest and 

 sample trees bear the ratio of the acreage occupied by the forest on the 

 one hand and by the sample trees on the other hand. 



