480 REARING OF THE ESTABLISHED CROP 



crops. In such crops the taller and more vigorous trees will not 

 always belong to the more valuable species, and must therefore 

 often be taken out for the benefit of individuals of these species ; 

 and besides this, many of the stems that require to be removed 

 may have wide crowns occupying a large space in the leaf-canopy. 

 Each thinning should therefore be effected in two separate opera- 

 tions. In the first operation the work should be confined to aid- 

 ing or relieving struggling individuals of the better species, 

 wherever it is certain that those of inferior kinds are not required 

 in the interests of the mixture. In the second operation, which 

 may sometimes bo usefully put off for a whole year, the attention 

 of the forester will be directed to the prosperous vegetation of tho 

 crop as a whole. 



When there are two stems standing so close to another as 

 to appear to have come up on one and the same stool, the weaker 

 or less valuable of the two ought to be got rid of, if the crop is 

 still young. But if the crop has attained a certain age, then it is, 

 as a rule, better to leave both stems standing, as the sudden isola- 

 tion of either of them may result in the unhealthy growth or 

 unsoundness of the other. 



VII. Concluding remarks . 



The foregoing remarks prove how important a part thinnings 

 play in the treatment and life of a crop and how much attention, 

 skill and judgment are required for their proper and timely execu- 

 tion. Those remarks also establish the general soundness of the 

 following grand rule, which should to be followed in every case 

 as closely as circumstances will permit : BEGIN EARLY, THIN 



MODERATELY, REPEAT FREQUENTLY. 



ARTICLE 2. 

 PLENARY THINNINGS. 



A plenary thinning is a very severe thinning made after tho 

 close of the period of ordinary thinnings, and having for its ob- 

 ject the complete isolation of the strongest and most promising and 

 valuable trees of a crop, so that they may spread out unchecked 

 and attain a giving diameter in as short a time as possible. The 

 thinning is usually severe enough to prevent the remaining trees 

 from meeting crowns for the next 30-40 years. The complete in- 

 terruption of the leaf-canopy necessarily implied in this system 

 of felling presupposes the absence of any risk to tho continued 

 protection of the soil, which protection is secured by means of 



