CHOICE OF SPECIES. 11 



cases a reduction of the fertility should be observed, 

 it will be due to insufficient shelter afforded by trees 

 with thin crowns, to heavy removals of litter, faulty 

 treatment, fires, or other causes. 



The fact that one species sometimes supplants 

 another is generally due to its greater reproductive power, 

 or its greater resisting power against external influences. 

 For instance, the felling of a Spruce or Scotch Pine 

 wood may be followed by the appearance of large 

 numbers of insects, which breed in the stools of the trees 

 left in the ground, and destroy any young crop of these 

 species which may spring up ; other species not sub- 

 ject to such attacks may then occupy the ground, if 

 allowed to do so. 



As a rule in Sylviculture a change of species is only 

 called for in special cases, such as : 



(1.) When the original species has, on general grounds, 

 been found unsuited for the locality. 



(2.) When an inferior species is to be replaced by a 

 more valuable one. 



(3.) When the fertility of the soil, in consequence of 

 faulty treatment, heavy removal of litter, &c., 

 has deteriorated, so that the original species will 

 no longer thrive on it, and must give way to one 

 less exacting. 



(4.) When a temporary shelter -wood (nurses) is 

 required for a tender species. 



(5.) When the object is to extend the growth of one 

 species uniformly over a certain area. 



