FORESTS AND THEIE CLIMATIC INFLUENCE. 397 



This inability of the vegetation to rise beyond a certain height, which 

 is lar from being that at which the to])S of such trees ordinarily sto]), 

 e%idently proves that there exists, at a greater or less elevation, a stra- 

 tum of air in which development in height is impossible. This effect 

 must be attributed to the air current of the desert, which is warm and 

 dry; all trees which grow in Algeria are subject to its influence. The 

 trees of the third group, the cypresses, the cedars, &c., which brave 

 this inllueuce, rise to a very considerable height. 



The principles above set forth suffice to show the part which for- 

 ests nmy play as a shelter, and within what limits they act. We are 

 naturally led to examine the value of the contradictory opinions re- 

 specting the effects of their removal, enunciated by Arago and Gay- 

 Lussac, in the commission appointed in 183G to consider the expediency 

 of adopting article 219 of the forest code. '' If the screen of forests on 

 the maritime border of Xormandy or Brittany," said M. Arago, " were 

 levelled, these countries would become accessible to the west winds, 

 the temperate winds coming from the sea. Hence there would be a 

 diminution in the cold of the winters. If a similar forest were cleared 

 away on the eastern frontier of France, the glacial wind of the east 

 would there be more powerfully propagated, and the winters would be 

 more rigorous: the destruction of a screen of this sort in the one and the 

 other situatiou would, therefore, haxe produced effects diametrically op- 

 posite."' 



In principle M. Arago was right, but not absolutely, for the eff"ects de- 

 pend on the locality where the forests are situated, on their altitude, 

 and on various other causes. 



M. Gay-Lussac used very different language : " In my opinion," lie 

 said, '• no i^ositive proof has thus far been obtained that woods have of 

 themselves any real influence on the climate of a large country or of a 

 particular locality, and especially that they have a different influence 

 from that of all kinds of vegetation. It might be asked if the evapora- 

 tion of water is tlie same ou a naked soil and one covered with vegeta- 

 tion. The questions are so complicated when considered under a cli- 

 matic point of view, that the solution is very difficult, not to say im- 

 possible. Another advantage in wooded soils which I do not dispute, 

 is to promote the abundance of springs of water. And all, in fact, that 

 teuds to arrest the flow of rain-water and to enable it to infiltrate slowly 

 into the earth, instead of passing off" in torrents, is favorable to such 

 springs. But once more, this advantage attributed to woods is pos- 

 sessed, in perhaps the highest degree, by a herbaceous vegetation ; 

 the close and numerous blades, the comose and interlaced roots, com- 

 pose a thick and spongy mass which admirably intercepts the move- 

 ment of the water, retains it, and yields it up by little and little," 



On the other hand, M. Beugnot, reporter for the commission named 

 in 18.51 to revise, as far as was needful, the forest code in matters re- 

 lating to clearings, denied, though with less authoritativeness than 

 MM. Gay-Lussac and Arago, the intluence exercised by great masses of 

 wood on the climate of a country. In his report he remarks : " The de- 

 partments of La Loire-Inferieure, La Mauclie, Le Pas de Calais, Le Xord, 

 La Somme, Le Maine-et-Loire, are among those which are least wooded. 

 Is the climate less salubrious than that of the Landes, of the Gi- 

 ronde, of Loiret, of Cher, and Loiret-Cher, which are among the most 

 densely wooded?" "We arrive," he adds, " at the same conclusion, on 

 comparing together the different countries of Euroi^e; consexiuently 

 the clearing away of woods is in nowise injurious to the salubrity of 

 the country." 



