. 288 A MANUAL OF FORESTRY. 



shelter-wood, the selection and group system being 

 perhaps even better suited to it than the compartment 

 system. The process of regeneration is a slow one. 

 In most mature Silver Fir woods groups of advance 

 growth are found, where operations may be com- 

 menced. By removing the shelter trees standing over 

 such advance growth, and gradually the adjoining trees, 

 regeneration extends all round, and the groups ex- 

 pand until they ultimately merge into each other. In 

 this way the regeneration period of a wood may extend 

 over 30, 40, and even 50 years. The old trees, being 

 gradually placed into an open position, increase rapidly 

 in diameter, volume and value. At the same time they 

 should be removed when the young crop demands it. 



i. Tending. 



Fertility of Soil. Silver Fir, if treated properly, is an 

 excellent preserver of the fertility of the soil. 



External Dangers. The young trees require shelter 

 against frost and drought for 10 and sometimes even 

 20 years. This is given either by the mother trees or 

 by an artificial shelter-wood of Larch, Scotch Pine or 

 Birch. This period passed, the tree is comparatively 

 free from danger. Storm and snow may do damage, 

 but not nearly so much as in the case of Spruce. Cattle 

 and deer nibble it, and the latter sometimes peel it, but 

 it heals such damage easier than the other Conifers. 

 Squirrels bite off the leading shoots. 



Insects are, on the whole, not very destructive. Two 

 species of Tortrix(2 T . murinana and rufimitrand] destroy 

 the needles and shoots, especially in Central Europe. 



