CHAP, viii.] Formation of Timber Crops 169 



financial advantage to see that due steps are taken to secure 

 this end. Now, with this object in view it is by no means 

 necessary to crowd plantations; for it is quite sufficient if 

 the twigs and branchlets die off before becoming strong 

 enough to leave snags or rotten ends in the timber, and if they 

 can be displaced by the new annual zones of wood. This 

 period varies with the different kinds of forest trees. The 

 branchlets of the ring-pored, broad-leaved species of trees rot 

 much sooner than those of conifers ; small twigs of Oak or 

 Beech snap off through their own weight when they have been 

 dry for two or three years; whilst similar twigs of Spruce 

 remain often as snags for ten or fifteen years, and get partially 

 embodied in the stem if not removed. For the production of 

 clean boles, therefore, conifers, and in particular the shade- 

 bearing kinds, should be maintained in close canopy consider- 

 ably longer than broad-leaved trees. 



When the normal density of canopy is exceeded that is, 

 when young woods are crowded the development of the 

 individual stem is injuriously affected ; for the crowns are 

 liable to be drawn up so rapidly as to exceed the normal 

 proportion which in well-developed trees should exist between 

 height and girth. Crowded thickets should consequently be 

 weeded and thinned as diligently as possible, even though this 

 may involve considerable outlay. Otherwise the maintenance 

 and prolongation of the individual struggle for supremacy on 

 the one hand, and existence on the other, may have a very 

 prejudicial effect on the ultimate remunerativeness of the crop 

 throughout all the later stages of its development. 



Where available, normal yield-tables in so far furnish hints 

 regarding the most advantageous density or initial number of 

 plants per acre in pure woods, that they show what the 

 minimum number should be at the various ages for the 

 particular genus of tree forming the crop on a soil of similar 

 average quality. Supposing, for example, it were found that 

 in Spruce forests, growing on soils of medium quality, the 



