THE SPRUCE INVESTIGATION. 



211 



Fig. VII. Spruce Forest, showing destruction by fire, and the rocky 

 condition of the surface on which the trees grow. 



SOME OP THE EARLY DISTURBING INFLUENCES. 



In a resume of the several influences which have tended to 

 lessen this forest area to its present comparatively small pro- 

 portion, we find that in addition to the destruction of the 

 forests by man, insects have taken a prominent part. 

 The changed conditions brought about by the early clearings 

 of the fertile valleys of the Greenbrier, Potomac, James 

 and Valley Rivers, and the rich country in the southern end 

 of the region, probably had the effect of materially reducing 

 the humidity of the atmosphere and soil, and of exposing the 

 more narrow and isolated mountain ranges of the eastern por- 

 tion to drying winds, forest fires (Fig. VIII) and fierce storms. 

 This naturally had the effect of weakening the vitality of the 

 spruce, and together with extensive wind falls, of which we 

 have some early records, the most favorable conditions were 

 offered for the increase and destructive invasions of spruce in- 



