FOGS, CLOUDS, HAILSTORMS, AND BLIZZARDS. 121 



INFLUENCE OF FORESTS ON FOGS AND CLOUDS. 



The iiifiueuoe of forests ou fogs and clouds has been frequently men- 

 tioned, and observed in single cases. The fog seems to linger in the 

 woods after it has cleared off elsewhere. Trees also act as condens- 

 ers,* as gatherers of dew, hoarfrost, and ice, and the latter phenome- 

 non is especially remarkable in the so-called ice-storms, where the ac- 

 cumulation is so great as to overload and break the larger limbs and 

 branches. In these cases, however, the tree acts like inorganic bodies. 

 This is illustrated by a celebrated case on the island of Ascension, the 

 details of which are due to Prof. Cleveland Abbe, who in 1890 per- 

 sonally inspected the ])henomenon. This case is especially worth quot- 

 ing because its records have been so badly understood. The principal 

 water supply for the garrison of this naval station is gathered several 

 miles away, at the summit of Green Mountain, the upper part of which 

 has always been green with verdure since the island was discovered; 

 almost all of this water comes from slight showers and steady dripping 

 of trees enveloped in cloud-fog on the windward side of the mountain. 

 Every exposed object contributes its drip; these do not condense the 

 water, they simply collect it mechanically after it has been condensed 

 in the uprising cooling air. Whatever fog-drops are not thus collected 

 SAveep on over the mountain and quickly evaporate again. Thirty years 

 ago or more efforts were made to plant a few trees in the arid spot at 

 the garrison landing; none survived, but some few new shrubs were 

 added to the flora of the mountain top; extensive additions were also 

 made to the mountain reservoirs and drip collectors and pipes of the 

 aqueduct system. The few artificial scrubby plants have had no influ- 

 ence whatever in increasing the water supply. 



INFLUENCE OF FORESTS ON HAILSTORMS AND BLIZZARDS. 



M. Becquerel found, by a careful study of the destructive hailstorms 

 in some of the departments of Central France, that these storms show 

 a marked disinclination to enter forests. On the maps of the depart- 

 ments studied by him he has marked the severe storms by spots of color. 

 A glance at the maps shows how persistently the colors keep outside 

 the forests, especially the larger ones. To controvert these views, 

 cases of hailstorms in forests have frequently been pointed out, but the 

 question is not of absolute but of relative immunity of forests from 

 severe hailstorms, and that these cases do not affect. The subject re- 

 mains where it was left by M. Be<*querel. It still appears proven that 

 in Central France hailstorms avoid forests. 



Many other relations of forests to storms have been suspected and 

 advocated. For instance, that the storm precipitation is more intense 



See p. 124 of this bulletin. 



