SILVICITLTURAL SYSTEMS. 



29 



ill by the wind and beechnuts carried and planted 

 by squirrels, and eventually the pure stand of spruce 

 is chang-ed into a mixed forest of various ages. As the 

 trees grow older, some of the spruce ma^^ be destro^^ed 

 by beetles or throw^n by the wind, and some of the 

 broadleaf trees may die from fungous disease. Into 

 the openings made by the death of older members of 



Fig. 16. — Lodgepole pine and western larch 

 in selection forest. Northern Idaho. 



the forest fall the seeds from which vouno-er members 

 spring. So little b}^ little the forest loses its even-aged 

 character and there comes into existence what is called 

 a Natural or Selection Forest, in which trees of all 

 ap'es are evervwhere closelv mixed too-ether. Most 

 virgin forests are selection forests. 



