CHANGE OF SYSTEM. 305 



Area to be dealt with during the first ten j-ears = 300 acres. 

 On this area all 120 jenvs old trees are cut, as well as the 

 necessary number of younger trees, so as to reduce them to a 

 suitable proportion. As it is a laborious matter to ascertain 

 the age of the trees, the diameter (or girth) at maturity is sub- 

 stituted for the age. For instance, instead of an age of 

 120 years, it may be laid down, that trees with a diameter 

 of, say, 2 feet at chest-height above the ground shall be 

 considered mature. At the same time it must be remembered, 

 that some trees will never grow beyond a certain size. These 

 must be cut, even if they have not reached the minimum 

 diameter (or girth) laid down for mature trees. 



The areas, to be dealt with in each period of, say, 10 j^ears, 

 should be marked off on the ground ; in some cases even the 

 annual coupes may be marked. 



A distinction between final and intermediate returns is very 

 difficult in the case of selection forests. 



To attempt a regulation of the expected returns by volume, 

 seems of doubtful utility. At any rate, to fix the yield in 

 material only, whether in cubic feet or number of trees, is a 

 risky procedure, which may lead either to over- or under- 

 working of the forest. By far the best plan is to fix the yield 

 by area, and to determine the minimum size of the mature 

 ti-ees to be cut. This area should not be exceeded. With this 

 reservation, the probable amount of final returns to be cut 

 may be estimated according to Brandis' or von Mantel's 

 methods to be described hereafter. The same precaution, as 

 in the case of coppice with standards, is here necessary ; care 

 must be taken not to cut more, than will be replaced by 

 increment, whenever fairly even annual or periodic returns 

 are expected. 



5. Cliaiific front one Sylricultural System to another, called 

 a Concersion. 



As a general rule, the returns during the period of con- 

 version are likely to be uneven in amount. If the new 

 F.:\i. X 



