THE THEORY OF THINNING. 295 



direct sowings and woods resulting from natural regeneration 

 generally require heavier thinning than plantings. 



iii. Rei'etition of Thinnixo.s. 



Thinnings should he repeated whenever they become 

 necessary. The more energetic the growth, the quicker 

 should the thinnings follow each other ; hence the intervals will 

 be comparatively short during the first half of life, and they 

 become longer with advancing age. For the rest, the length of 

 the intervals depends on the species and the quality of the soil. 



A frequent repetition of the thinning should not be replaced 

 by thinning too heavily at any particular time ; such a 

 measure would not secure the most favourable development 

 of the dominating trees. 



In summing up it may be said that, where the object is to 

 produce quantity, the thinnings should commence early, be 

 heavy, and frequently repeated during the first half of the 

 life of a wood, and be more moderate and repeated at longer 

 intervals during the second half. 



h. Pr(i(hirHoii of Hiijli-rhis>< Thnhcr. 



Where the production of high-class timber is aimed at, 

 quantity must to some extent be sacrificed. Trees fit to yield 

 such timber must answer the following description : — 



(1.) The boles must be tall, straight, free of branches, and 

 as litt'e tapering as possible. 



(2.) Differences in the breadth of the concentric rings must 

 be slight. 



(3.) The timber must have a high degree of density. 



Boles free from branches and non-tapei'ing are not produced, 

 if heavy thinnings are made at an early age of the wood ; at 

 any rate not in the same degree as if the wood were kept 

 dense, when the lower branches are more rapidly killed for 

 want of light. Pruning cannot make up for this, though it 

 can do something. 



There is naturally a tendency to produce broader rings 

 during youth than later on ; heavy thinning at an early age 



