080 JOURNAL OF FORESTRY 



on the Continent, in which the diameters are measured by callipers, 

 for the following reasons : 



(1) The quarter-girth system is always used in practice in Great 

 Britain. 



(2) The tape is the simplest method of measurement, and requires 

 less physical effort than the callipers, an important point when the 

 measurements were carried out by women. 



(3) A comparative series of measurements were made with tape 

 and callipers on about 2,000 trees. The test was complicated by the 

 difficulty of obtaining reliable callipers, but the conclusion reached was 

 that where both methods of measurement are accurately carried out 

 the dift'erence in result is negligible. 



A grand total of I.IUO sample plots and sub-plots was measured in 

 the three countries. Of these 4K1 were European larch. 334 Scots 

 pine, and 157 Norway spruce. 



It was decided to base the classification of woods upon height rather 

 than upon volume, and the following system was adopted : 



The sample plots were classified according to the height reached at 

 a standard age. An age of 50 years was selected for the following 

 reasons : 



(a) By the time a coniferous wood is 50 years old all the factors of 

 locality should have found decisive expression in the growth of the 

 crop, and the height growth at that age should be a reliable index to 

 the quality of the wood. Exceptions occur, but are not likely to be 

 numerous. 



(b) It' was desirable to take the lowest age at which these factors 

 had produced decisive effect, as, the lower the standard age, the fewer 

 sample plots need be excluded from the preliminary classification and 

 the more data will be available for constructing the height curves upon 

 which the final classification depends. 



The range of height class in larch and spruce is from SO to 40 

 feet, and in Scots pine from 60 to 40 feet. In the first two species the 

 quality classes are numbered from I to V, quality I being the 80-foot 

 class and quality V the 40-foot class. In the case of Scots pine the 

 quality classes are numbered from I to III, quality I being the 60-foot 

 class and quality III the 40-foot class. .Sample plots belonging to 

 poorer qualities than the 40-foot class were measured in all three 

 species, but there were not sufficient data from which to construct 

 curves or tabular statements. 



Yield tables have been constructed on the above lines for larch and 

 spruce in the British Isles and separately for Scots pine in England 

 and Scotland. The division of the Scots pine was rendered necessary 



