136 FOEESTRY WORK 



will be drawn up into long, weakly stems, unable to 

 stand against wind or under heavy falls of snow. 



To prevent this some of the poles must be taken out. 

 This is called " thinning." 



The principle of thinning may be said to be to allow 

 sufl5cient room for the development of the best trees, 

 without admitting too much light, which would prevent 

 the killing of the side-branches and also prevent decay 

 of the humus, thus depriving the trees of their source of 

 nutriment. 



The trees before thinning will be — (1) Dominant, those 

 trees above the normal height; (2) dominated, healthy 

 trees about the normal height, but overshadowed by the 

 dominant class; (3) suppressed, including all dead and 

 dying trees and those prevented from developing by the 

 more vigorous trees. 



The latter class should all be removed, except healthy 

 but stunted trees, the removal of which might cause too 

 large a break in the canopy. 



The French method is to cut out all dead and sickly 

 stems and leave all healthy but suppressed trees for the 

 protection of the soil, only pruning or removmg those 

 that are doing injury to better trees. In the dominated 

 class only those trees that are interfering with the growth 

 of others need be removed. 



Dominant trees, especially if of an inferior species, 

 having been used as nurses to more expensive varieties, 

 should be removed if the growth of their crowns is proving 

 injurious to any of the latter trees. 



The age at which to commence thinning varies with 



