OF AVHOLE WOODS. 93 



time, since the wood was created. Height growth alone makes 

 an exception. An analysis of a number of sample trees will 

 indicate the mean height of these trees during previous periods, 

 M'hich may be taken as the upper height of the wood at those 

 times. These would, of course, not represent the mean 

 heights at the several ages, because it may safely be assumed, 

 that the now existing trees were, as a rule, always the leading 

 trees. Investigations have proved, that the mean height of 

 woods can be deduced from the upper height. For instance, 

 in the case of the Scotch pine the difference ranges from 

 about 3 to 5 per cent, according to the age of the wood. 

 But no such relation has as yet been found as regards the 

 basal area or the volume, and to evolve the former amounts of 

 these out of the present quantities is more or less speculative. 

 Under these circumstances one of the two methods about to be 

 described may be followed. 



A. Determination of the Future Increment according to 

 the Mean Annual Increment of the Past. 



The present volume of the wood is ascertained and divided by 

 its age, the quotient giving the mean annual increment, calcu- 

 lated on the growing stock present at the time of measurement. 

 According to the age of the wood, it may be assumed, that the 

 mean annual increment will be laid on for a number of years 

 to come, or a somewhat diminished or increased increment. 



The method gives fair results, if the calculation is made for 

 the time, when the mean annual increment culminates and even 

 for older woods; it is less accurate in the case of younger woods. 

 Moreover, it is only applicable for a limited number of years. 



B. Determination of the Increment by means of 



Yield Tables. 



/.—Of Yield Tables Generally. 



1. Befiniiion of Yield Tahles. 



It has already been explained, that the progress of height, 



diameter, basal area and volume increment can be rejn'e- 



