OKDINAKY THINNINGa, THEIR ADVANTAGES. 471 



verity of forest conflagrations, keep down the numbers of wood- 

 eating insects at the lowest limit possible, and restrict, if not 

 entirely prevent, the attacks of destructive ftmgi. 



(c) They augment very remarkably the sum total of production 

 of a given area. Trees under suppression have practically ceased 

 to increase in size, while their presence not only prevents their 

 neighbours from spreading out as freely as they might, but may 

 even weaken them through overcrowding. They are thus not 

 merely superfluous, but positively harmful. Their removal would, 

 therefore, have the twofold effect of immediately reaJising a not 

 inconsiderable amount of more or less valuable produce, which 

 would otherwise have been entirely lost,, and of giving increased 

 growing room to their vigorous neighbours, which would not be 

 long in expanding themselves and completely filling up this addi- 

 tional space. What is true of trees under suppression is also to 

 a greater or less exteiri; true of those which are beginning to be 

 suppressed. Remembering these fe,cts,. let us consider what hap- 

 pens in any given forest-covered area. We know that at any given 

 age it is not capable of yielding more- than a certain maximum 

 quantity of wood ;. so that if at that age this maximum quantity is 

 standing on the ground, no further increment is possible. But if 

 some of the weaker individuals be now taken out, we know that 

 the remainder will at once spread themselves out until the addi- 

 tional room made for them is once more filled up and the maximum 

 production is again standing on the ground. Thus it becomes 

 obvious that thinnings not only yield a large outturn of valuable 

 produce, but also constamtty maintain on the ground the maximum 

 crop that the area in question is able to support at successive ages. 

 We have as yet no rigorously accurate data regarding the total 

 yield of thinnings ; nevertheless German foresters believe them- 

 selves justified in asserting that it is in their country from 20 to 

 33 per cent of the total yield of the crop,* and that if the rotation 

 be rightly chosen, it may aggregate as much as from one-fourth, 

 to one-third the yield of the regeneration fellings. Considered 

 absolutely, it reaches its highest figure in conifer forests and on 

 rich soils ; but cwisidered relatively to the total yield,, it is proper^ 

 tionately higher on poor soils. The average annual yield of thin- 



• Gayer's figures have been adopted here, but Heyer says- that, with a weU-ohosen 

 rotation, the yield of thinnings will average from one-fourth to one-third the entire 

 yield of the crop, and from one-third to one-half the yield of the exploitable crop.. 

 Bagneria in France goes farther and states that for some species the outturn from 

 thinnings may sometimes equal that of the regeneration fellings ; but it is to ba 

 remem^red that in that country preparatory regeneration fellings are classed a» 

 thioiiinga. See Appendix A. 



