64 BOTANICAL SURVEY OF THE C05UR 1)'ALENE MOUNTAINS. 



were employed, but added to them axe the fires, and they spare neither 

 old nor young growth. 



There are two principal agencies by which growing timber is de- 

 stroyed — the operations of nature and those of man. 



The natural agencies operating in the < Joeur d'Alenes are in part those 

 ot the meteorological order and in part those which act as diseases of 

 the trees. Of the former there are four, rain, snow, lightning, wind; 

 of the latter, (me, fungi. 



The action of rain, snow, and wind is more or less synchronous, accord- 

 ing to season, and operates throughout the year. The lightning is more 

 local, and limited to a few months during late spring and summer. 

 The destruction from the first three climatic agencies, resulting from 

 the enormous precipitation, is immense. The vast quantities of debris 

 in the shape of fallen or broken trees, which litter the forest in all direc- 

 tions, prove this. The storms that bring the rain or snow are nearly 

 always accompanied by strong south or southwesterly gales. Owing 

 to the broken character of the mountains, the valleys are sheltered 

 from the direct force of the wind, which is only felt in all its strength 

 on the high summits of the ridges. In the valleys the wind comes in 

 series of severe gusts of longer or shorter duration. The heavy rains 

 loosen the soil and humus about the roots of the trees, and their great 

 height affords a leverage by which the largest tree is easily overthrown 

 by a comparatively small exertion of force. The ease with which a 

 tree is thrown down depends, also, largely upon the depth to which the 

 roots penetrate. There are but two species of conifers of general occur- 

 rence in this section which strike root deep enough to offer a fair degree 

 of resistance to the wind. They are the cedar and Western tamarack. 

 The cedar is short in stature and does not offer much leverage; the 

 tamarack grows tall and, as it does not readily yield at the root, is 

 frequently broken off in the trunk. We therefore find the greatest 

 destruction due to these agencies in the Intermediate or White Pine 

 Zone. 



The operation of the phenomenon that 1 have named the dominant 

 precipitation point (see page l~>) is shown here. It has already been 

 mentioned that the winds which accompany the storms are felt through- 

 out the valleys as powerful intermittent gusts. The greater number of 

 these are observed to have a certain determinate direction for each sea- 

 son, breaking down the forest persistently and repeatedly in the same 

 locality during successive storms and leaving other portions untouched. 

 As the ridges by their trend determine in the deflection of the air cur- 

 rents the angleof impact of the wind in the valleys, it will be readily seen 

 that a change in the general direction from which the storms come will 

 involve a corresponding change in the deflection of the air into the 

 valleys, which, in turn, will spend its force upon another part of the 

 forest. If the storms came always unalterably from the same point, 

 we should have long, tortuous passages cut through the forest in certain 



