TREES AS SHELTER TO GROUND TO THE LEEWARD. 157 



great swamps of Virginia and the Carolinas, in climates nearly 

 similar to that of Italy, are healthy even to the white man so 

 long as the forests in and around them remain, but become very 

 insalubrious when the woods are felled,* The " Dismal Swamp," 

 pai-tly in North Carolina and partly in Yirginia, is said to be an 

 entire misnomer. There is nothing dismal about it excej)t its 

 general solitude. It is described by recent visitors as a capital 

 resort for sportsmen, game being abundant, and fish ready to rise 

 to the fly. The most curious features of the swamp are the 

 sweetness and wholesome character of the water, and the entire 

 freedom of its few inhabitants from malarious diseases. This 

 purity is ascribed to the influence of the juniper tree, which cer- 

 tainly colors if it does not improve the water, and possibly con- 

 tributes an antiseptic property to the air. 



Trees as Shelter to Ground to the Leeward. 



As a mechanical obstruction, trees impede the passage of air- 

 currents over the ground, which, as is well known, is one of the 

 most efficient agents in promoting evaporation and the refrigera- 

 tion resulting from it.f In the forest, the air is almost quiescent, 



* Except in the seething marshes of northern tropical and subtropical re- 

 gions, where vegetable decay is extremely rapid, the uniformity of tempera- 

 ture and of atmospheric humidity renders all forests eminently healthful. 

 See HoHENSTEnsf's observations on this subject, Der Wold, p, 41 ; also A. 

 Matjky, Les ForeU de la Gaule, p. 7. 



The flat and marshy district of the Sologne in France was salubrious until 

 its woods were felled. It then became pestilential, but within the last few 

 years its healthfulness has been restored by forest plantation. — Jules Clave 

 in Bei>ue des Deux Mondes, for 1st March, 1866, p. 209. 



There is no question that open squares and parks conduce to the salubrity 

 of cities, and many observers are of opinion that the trees and other vegeta 

 bles with which such grounds are planted contribute essentially to their bene- 

 ficial influence. See an article ia Aus der Natur, xxii., p. 813. 



f It is perhaps too much to say that the influence of trees upon the wind is 

 strictly limited to the mechanical resistance of their trunks, branches and 

 foliage. So far as the forest, by dead or by living action, raises or lowers the 

 temperature of the air within it, so far it creates upward or downward cur- 

 rents in the atmosphere above it, and, consequently, a flow of air towards or 

 from itself. These air-streams have a certain, though doubtless a very small, 

 influence on the force and direction of greater atmospheric movements. 



