94 ROTATION. FOE; QUANTITATIVE'. EXPLOITABILITT. 



Working Circle that has to- be organisedy for we have to consider' 

 net this or thati particular portion of the Working Circle- but the 

 ■whole of it as- an organic unit. The age of the youngest of the ■ 

 trial crops need not be less than that at which-^the stock, becomes 

 marketable, and it- matters little How great the difference is between, 

 the respective ages- of :any two of these crops; but one condition 

 they must all fulfil, they should be dense enough to- require being 

 thinned. Ihthefiist place, unless they be so, they cannot be con- 

 sidered to be as complete as psssible;- and in the next place, once- 

 th«cubical contents of the standing wood in each has been estimated, 

 ■we can' at once proceed to thin and measure up the quantity thin- 

 ned' out. The produce yielded by a crop in thinnings is a^ quantity 

 that must be known, in. order to enable one toxical with the older 

 trial crops.. 



After- the thinning in any given crop has been mad«, the 

 Humber of the trees remaining should be counted. The next older 

 Grop should contain, before being thinned, the same number of trees 

 more or less, for it is evident that it is only by comparing the 

 Bwrnber of trees standing at different ages that we can- be sure that 

 the crops have been suitably selected and that eacb crop, is an exact 

 counterpart of the- immediaftely younger one modified by time. The 

 degree of fertility of the soil in the several crops has to be the same, 

 and there is nothing to indicate this except equality of the number 

 of the trees in any two consecutive crops, the younger one taken 

 after, the older before, being thinned, it being granted that each 

 of these crops is as full as it can be. The reason of this is clear, 

 for it is obvious that the number of trees standing in any full crop 

 is inversely proportional to the fertility of the soil. 



A complete series of such experiments can rarely be made in 

 the same Working Circle, since for this purpose it would have to 

 contain in itself every one of the trial crops required, all of them as 

 full as possible and representing the different stages of the same 

 ideal crop. Now there are even species (like the silver fir, for 

 instance, which was formerly everywhere treated on the Selection 

 System) that form only in exceptional cases crops composed of trees 

 of the same age. Another difficulty is that it is only recently that 

 regular thinning operations have been adopted as an integral and 

 necessary part of the treatment of forests, the consequence being 

 that in existing crops Ci any age they have been made only since 



