CHAPTER IX. 



WIND. 



Among the sudden effects of severe wind are the injuries known as 

 "uprooting of trees by wind" and "breaking of tree trunks by wind." In 

 the first, the trunks of the trees are thrown over to one side, taking the root 

 systems with them. In the second, which is economically more injurious, 

 the trunk is broken off. 



The action of the storm depends upon the variety of the trees, the 

 stiffness of the individual trunk and its location. In regard to the variety, 

 it may be remarked that tough wooded genera, like birch, spruce, hornbean 

 and redbeech are more often overthrown than broken. Pines and oaks 

 break more easily. The kind of break also differs with the genus. It 

 seems as if pines break off shorter, while the oak splinters and the brittle 

 acacia often shows deep clefts on the stump, extending downward from the 

 broken surface. In regard to the individual firmness of the trunk in the 

 same variety, it is evident that trees, rotten at the core, break most easily. 

 The individual structure of the tree top. which forms the chief point attacked 

 in the lever represented by the trunk, is likewise of importance. The 

 position and the local conditions influencing the structure of the root system, 

 essentially under consideration here, are of the most extensive influence. In 

 deep soil, those trees will endure more wind which have not been trans- 

 planted, since in transplanting the tap root has been cut off to make the 

 moving easier. In shallow soil, the advantage of the tap root is lost and 

 the development of the top becomes the important factor. The higher the 

 branching begins on the otherwise smooth trunk, the higher is the centre of 

 gravity, and the more liable the tree is to be uprooted or broken. Pyra- 

 midal crowns are therefore probably better than those of a dense spherical 

 form. There are naturally exceptions to the rule; the more exposed the 

 location of the tree, the greater the danger of injury. On mountain slopes 

 it is often noticed that injury due to storms, especially in uprooting the 

 trees, is far less extensive on the windy side than on slopes on which the 

 storm passes downward. Further, whole groups will be overthrown often 

 in the centre of an uniformly old tract of trees. This may be explained by 

 the fact that the wind, in blowing upward, is more uneven and can effect 

 only a small part of the crown of one tree because another standing lower 



