216 A MANUAL OF FORESTRY. 



There is naturally a tendency to produce broader 

 rings during youth than later on ; heavy thinning at 

 an early age increases the difference, leading to the for- 

 mation of trunks which consist of a number of broad 

 rings in the inner part, surrounded by a series of narrow 

 ones. Such timber is for many purposes of smaller 

 value than if the rings are of uniform breadth 

 throughout. 



As regards the density of the timber, a distinction 

 must be made between the various species. In the case 

 of those broad-leaved species which have the pores in 

 the spring-portion of the wood, broad rings indicate high 

 quality, and narrow rings comparatively low quality; 

 here then, heavy thinnings are indicated. The same 

 probably holds good for species which have the pores 

 uniformly distributed over the ring. In conifers, how- 

 ever, the matter is exactly the reverse. There, broad 

 rings represent inferior quality and narrow rings the 

 reverse ; consequently heavy thinnings must be avoided, 

 at any rate up to a certain age. 



On the whole it may be said that, in the production 

 of high-class timber, heavy thinnings at an early age 

 should be avoided. The rule here, according to which 

 the thinnings are to be made, must run as follows : 



The wood should be thinned lightly until towards the 

 end of the principal height-growth ; then the thin- 

 nings should gradually become heavier, so as to assist 

 a selected number of trees by the gradual removal 

 of all those which are inferior and diseased. In other 

 words; the thinning is done more in the dominant and 

 dominated trees than in those which have been left 

 behind in the struggle for existence and no longer com- 



