6 



COMPLETE YIELD TABLES FOR BRITISH WOODLANDS 



timber in various lengths by estimating the amount of 

 "taper" and so on, as is now customary. 



In these tables the form factors for timber down to 

 3 inches in diameter are given, but other form factors, 

 giving the amount of timber down to 5 or 6 inches 

 quarter girth, might well be prepared. 



It is necessary to remember that these form factors 

 are referable to measurements in which fractions of ^ 

 an inch in quarter girth are omitted, so that in the 

 following tables there is often a considerable difference 

 between the contents, as stated, of an average tree at 

 any particular age and the contents indicated by the 

 height, quarter girth, and form factor. But in all cases 

 an average form factor has been stated. 



With regard to the form factors for the broad-leaved 

 trees, they must only be regarded as correct if the trees 

 have been grown under somewhat similar conditions to 

 those as indicated in the tables. They are not applic- 

 able to short, stunted crops which in their youth have 

 been over-thinned. 



These form factors, if applied, will give contents 

 which indicate that the timber has all been measured 

 with string in a practical manner, according to the 

 custom of the country. 



The form factors as obtained from German yield 



tables have, in practice, no value whatever in this 

 country. They have an academic interest, but that is 

 all. For they are obtained by measuring a tree in small 

 sections, the diameters being taken with calipers and 

 booked to the equivalent of decimal parts of an inch, 

 thereby giving theoretically accurate measurements. But 

 in this country, if form factors are used, it is imperative 

 that they give correct results according to the prevail- 

 ing practice adopted by practical timber measurers. 



Now, besides the great losses entailed " in the fold 

 of the string " (vide p. 3), it is customary to omit fractions 

 of ^ an inch in the quarter girth ; and so also trees are 

 measured in long lengths (unless there are "stops"), 

 and not in small sections of 5 or 10 feet. 



Thus it will be evident that these variations in the 

 methods of measuring will make an enormous difference 

 to the form factors, according to whether they are 

 obtained by British methods or German methods of 

 measuring timber. 



These discrepancies are very much greater in the 

 case of small timber than in the case of large timber. 



The Percentage Increment. The two columns 

 which show the percentage increment which takes 

 place from period to period in volume and in value 



