THE THEORY OF THINNING. 293 



from them ; in the meantime, only the results of general 

 observations are available for guidance. 



It has been explained above that, during the struggle for 

 existence, four different classes of trees are produced, namely, 

 dominating, dominated, suppressed, and dead trees, and the 

 question arises in how far each of these should be interfered 

 with at each thinning. It is obvious that the dead trees must 

 be removed at every thinning, as they cannot influence the 

 other tliree classes, while their presence in the wood is a 

 constant source of danger from insects and fungi, and in some 

 cases from fire. Whether, and to what extent, the suppressed 

 trees, the dominated and dominating trees should be removed 

 depends, apart from species, chiefly on the character of the 

 locality and the objects of management. On fertile soils an 

 interruption of the cover overhead is of comparatively small 

 importance, but on inferior and even middling soils this should 

 be avoided. In such cases the dominated and even suppressed 

 trees, or at any rate a portion of them, must be retained 

 whenever the dominating trees alone are not sufficiently 

 numerous to provide a complete leaf canopy. If, on the other 

 hand, the number of dominating trees is so large that they 

 interfere with each other's proper development, a portion of 

 them may also be removed. 



As regards the objects of management, it suffices in 

 practical sylviculture to distinguish between the following 

 two cases : — 



(a.) Production of the greatest quantity of material. 



(b.) ,, ,, highest quality ,, 



In some cases the two objects may be realised by an 

 identical treatment, in others the one demands a method 

 of thinning different from that which is desirable in the 

 other. 



a. Productiun of the n recited QuanHtij of Material. 



Experience has shown that the greatest quantity is produced 

 in the shortest possil)le time by a vigorous development of the 



