206 A MANUAL OF FORESTRY. 



mentioned is specially recommended, whera the use of a 

 ladder is not preferred. 



Wounds which are so large that they are not likely to 

 be speedily closed by occlusion, must receive a water- 

 proof covering; this is necessary even in pruning 

 large branches of coniferous trees. 



The most suitable covering consists of a layer of coal 

 tar, made sufficiently fluid by an addition of oil of 

 turpentine, and laid on with a brush. The artificial 

 covering will only stick on when the sap is down ; hence 

 in temperate Europe the best time for pruning is 

 autumn and the first half of winter. Dry branches, 

 and snags may be cut off at any time of the year, pro- 

 vided the living tissue of the tree is not injured during 

 the operation. 



According to E. Hartig, pruning green branches 

 while the tree is in sap, causes a somewhat rapid decom- 

 position of the wood near the wound. For this reason, 

 also, pruning in the first half of winter is recommended. 



C. Thinning. 

 1. General. 



One of the most important objects in the formation 

 of a wood is to stock the area sufficiently, so that a 

 complete cover overhead may be established as early as 

 possible. This is desirable, not only for the preserva- 

 tion of the soil, but also for a proper development 

 of the trees. In order to ensure quick closing 

 overhead, it is necessary to bring on to the ground 

 a much larger number of plants than can find room 

 on it for any prolonged period. Soon after a complete 



