SILVICULTUKAL 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 destroyed 

 by beetles or thrown 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 younger members 

 spring. So little by 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 everywhere closely mixed together. Most 

 virgin forests are selection forests. 



