134 FOEESTRY WORK 



some immune species must again be used, although in 

 this particular instance it is hard to find a species that 

 is immune, as they even gnaw hardwoods. 



Where blanks are still found in older plantations, any- 

 self-sown trees should be allowed to grow to fill the 

 spaces. Birch is often verj'' useful in this respect. 



In crops that have been sown, blanks will be found, 

 and these should be filled up with plants taken from 

 spots where they are too thick upon the ground. The 

 cylindrical spade is extremely useful for this, as the 

 plants may be lifted and carried direct to their new 

 quarters with the minimum of disturbance. 



Weeding and Thinning. 



The object of planting trees closely together and 

 keeping them in close canopy is to produce long, clean, 

 straight and cylindrical stems. 



If planted too far apart or thinned too heavily, thus 

 admitting too much light, the resultmg trees are short, 

 tapering, and covered with branches. In self-so-wTi 

 forests the seedlings come up very thickly, and the 

 struggle for the survival of the fittest begins almost at 

 once. In a plantation this struggle begins as soon as 

 close canopy has beeu formed — i.e., when the side- 

 branches have met and covered all the spaces between 

 the trees — when each tree strives to outgrow its neigh- 

 bours. The results are that first the lower branches are 

 suppressed, then gradually the more vigorous trees 

 dominate and, later, suppress the weakly ones. 



To leave these dead and sickly trees in a plantation is 



