NATURAL ENEMIES OF THE FOREST. 231 



shallow soil underlaid with solid stone, especially where open spaces 

 give the wind free sweep. It follows that an unbroken forest is a 

 great protection to itself. The only precautions against wind there- 

 fore, that can be taken by the forester, are to keep the forest unbro- 

 ken by selecting only the larger trees for felling or to cut down a 

 given tract by beginning at the side opposite the direction of pre- 

 vailing storms and working toward them. 



In sandy regions, the wind does immense harm by blowing the 

 sand to and fro in constantly shifting dunes, Figs. 75 and 76. These 

 dunes occupy long stretches of the Atlantic coast and the shore of 

 Lake Michigan. Such dunes have been estimated to cover 20,000 

 square miles of Europe. Along the Bay of Biscay in France, the 

 sand dunes formerly drifted in ridges along the shore, damming up 

 the streams and converting what was once a forest into a pestilential 

 marsh. This region has been reclaimed at great expense by building 

 fences along the shore to break the wind and thus keep the moving 

 sand within limits. In this way a million acres of productive forest 

 have been obtained. 



On the other hand winds are beneficial to the forest in scattering 

 seeds, weeding out weak trees, and developing strength in tree trunks. 



Drouth both injures the foliage of trees and causes defects in the 

 grain of wood, the latter appearing as "false rings." These arise 

 from the effort 

 of the tree to 

 resume growth 

 when the water 

 supply is re- 

 stored. See p. 19. 



Water. Cer- 

 tain trees have 

 become accus- 

 tomed tO living Fijr. 77. , Effect of Flooding. First Cotin^cticuT 

 in much Water Lake, New Hampshire. 17. S. forest Service. 



as cedar and cypress have in swamps, and certain trees have become 

 accustomed to periodical floods, but other trees are killed by much 

 water. So when lumbermen make a pond which overflows forest 

 land, the trees soon die, Fig. 77. 



Lightning frequently blasts single trees, and in dry seasons may 

 set fire to forests. This is a much more important factor in the west 



