34 PROTECTION OF WOODLANDS. 



CHAPTER III. 



DAMAGE CAUSED BY AERIAL CURRENTS. 



22. Damage done ~by Storms. 



Violent movements of aerial currents are commonly called 

 Storms, and those of still greater violence Hurricanes. 1 Sometimes 

 they are merely of a local character, but at other times they 

 make their influence felt over large areas, and either come from 

 a certain definite direction as continuous storms, or have a more 

 or less circuitous movement as in cyclones. Most of the storms 

 in Great Britain come from the west, north-west, or south-west, 

 and their injurious influence is increased by the fact that they 

 are frequently accompanied by rainfall, and either loosen the 

 soil, or find it in soft, wet condition, which materially weakens 

 the resistive power of the trees, whilst the less frequent and 

 usually less violent east winds generally bring drought or fi 

 along with them. Violent disturbances of the atmospheric 

 rents are most usual about the time of the spring and auti 

 equinoxes, and the periods immediately connected therewith. 



During violent storms, not only individual trees but also whole 

 woods are either rendered windfall by being torn out by the 

 roots and thrown to the ground, or suffer wind-breakage by being 

 snapped through at a greater or less height above the base; 

 whether windfall or breakage is more likely to take place depends 

 on the species of the tree, the nature of the soil, the general health 

 of the stem, &c. The damage done is sometimes confined to indivi-' 

 dual trees, but not infrequently extends, in the case of very violent 

 storms, over whole crops or portions of crops, and in the latter case 

 takes place in scattered patches or plots, or else in strips or lanes. 



The disadvantageous consequences which can ensue to a forest 



1 Aerial currents shown by the anemometer to have a velocity up to 66 feet (2( 

 metres) per second are classified as Winds ; those whose velocity is from 66 to 116 fee 

 (36 metres) as Storms ; those beyond 116 feet (35 metres) per second as Hi( 



ana 



= 



