28 North American Forests and Forestry 



ing to the measure of its exposure ; that is, a tree 

 growing in a place where strong winds are con- 

 stantly blowing, as on the crest of a high mountain, 

 develops as deep and stout a root, and strengthens 

 its other wind defences just as much as its specific 

 nature will permit. On the other hand, a tree 

 growing in a protected ravine does not waste energy 

 on such useless objects, but puts it into other forms 

 of life activity. The trees in the midst of a com- 

 pact forest protect each other, and consequently 

 develop relatively shallow root systems. Only 

 those at the edge of the wood, where the wind can 

 reach them better, send their roots down deeply. 

 Now suppose that, either by the hand of man or 

 natural causes, an opening is made in the forest, so 

 that individuals which heretofore stood surrounded 

 by trees are now exposed to the wind on one or 

 more sides. The trees now forming the edge of 

 the wood will at once proceed to strengthen their 

 root systems and thicken their boles, until they are 

 as well prepared to resist the violence of the wind 

 as if they had grown in an exposed situation from 

 the beginning. But this process takes a number 

 of years, and in the meantime they are in constant 

 danger of being uprooted or broken off. Undoubt- 

 edly the majority of disastrous windfalls are in 

 situations like the one described, where the trees 

 had not yet become adapted to new conditions. 

 But it may happen, of course, that a storm of un- 

 usual violence overthrows trees which had bravely 

 withstood all ordinary tempests. The trees some- 



