TENDING OP CROWDED WOODS. 217 



pete ; the latter may even be left to assist in the pro- 

 tection of the soil. Deviations from this rule are to 

 some extent admissible in the case of species having 

 their pores in rings, when heavier thinnings may com- 

 mence at a somewhat earlier age, in so far as they do 

 not prevent the clearing of the boles. 



4. Thinning of Mixed Woods. 



In the foregoing pages the theory of thinning as 

 applicable to pure woods has been given. Generally, 

 the points aimed at are to stimulate production and to 

 develop the most suitable individuals for the final crop. 

 In mixed woods a third consideration presents itself, in 

 the preservation of a suitable mixture without inter- 

 fering with the maintenance of a sufficient leaf -canopy ; 

 this often leads to deviations from the theory as indi- 

 cated above. 



In the case of mixed woods it may often be neces- 

 sary to remove a dominant tree of one species because 

 it threatens to suppress a tree of another species, 

 which must be preserved for the sake of the mixture. 

 To guard against an interruption of the cover in such 

 cases, the dominated and even suppressed trees must 

 be more carefully husbanded than in pure woods, until, 

 with the advancing age of the wood, the mixture has 

 been secured. Frequent and light thinnings are in 

 such cases indicated. Their actual degree depends 

 much on the light requirements of the valuable species 

 in mixture. The operation is much facilitated if the 

 several species are mixed in groups instead of by 

 alternating single trees. 



Where a valuable timber species is mixed with a less 



