SILVICULTURAL SYSTEMS. 



29 



in by the wind and beechnuts carried and planted 

 by squirrels, and eventually the pure stand of spruce 

 is changed into a mixed forest of various ages. As the 

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

 by beetles or thrown bv the wind, and some of the 

 broadleaf trees may die from fungous disease. Into 

 the openings made b}^ 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 younger 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 

 ages are evervAvhere closely mixed together. Most 

 virgin forests are selection forests. 



