64 FORESTRY 



to have certain cuttings or thinnings periodically. The fre- 

 quency with which thinnings should be repeated is determined 

 by the energy of growth shown in the wood's development ; 

 in young woods the interval is generally about five or six 

 years, and in older woods, ten years. 



In order to have some sort of guide for the carrying out 

 of the thinnings, a division has been made classifying the 

 trees of a wood according to their crown development. 

 Two great sections may be recognised the dominant and 

 the secondary trees. To the former class belong those 

 which, possessing well-formed crowns, occupy the upper 

 position in the crop. The main mass of their foliage may 

 also be said to be at a fairly equal height from the ground. 

 The secondary trees comprise the lagging, overtopped, and 

 dying stems. 



The boundary between the two groups is, "of course, not 

 sharply drawn, and there is a constant process going on 

 whereby members are crowded out of the principal into the 

 inferior class. Occasionally, but more rarely, a portion of 

 the crop raises itself from the latter to the former rank. 



Up to the present, thinning has been conducted on the 

 principle that the material to be removed should be looked 

 for only amongst the secondary class of stems, and that the 

 dominant trees ought not to be interfered with unless under 

 quite exceptional circumstances. This has been the view 

 held in Germany until recently, and it has obtained currency 

 in Britain also. 



Thinnings were distinguished as of three grades : 



(1) Light thinning: the removal of dead and dying 



trees. 



(2) Moderate thinning : by which, in addition, the 



suppressed trees are taken. 



(3) Heavy thinning : when also lagging members 



i.e. those with somewhat reduced crowns that are 

 being pressed upon from the side by dominant 

 trees are cut into. 



