314 M. BECQUEKEL, ON THE CLIMATIC EFFECTS OF' FORESTS. 



This inability of vegetation to rise above a certain height, ranch below 

 that at which the tops of these trees commonly stop gaining in altitude, 

 evidently shows that at an elevation greater or less, there exists a 

 stratum of air where further gain in height is impossible. This effect 

 should be ascribed to the atmospheric currents from the desert, which 

 are hot and dry ; and all trees growing in Algeria yield to its influence. 

 Trees of the third group, the cypresses and cedars, brave this influence 

 and grow to a greater height. 



The principles we have stated, serve to show the part that forests play 

 as a shelter, and the limits to which this efl'ect extends. We are natu- 

 rally led to examine and estimate the contradictory opinions expressed 

 by Arago and Gay-Lussac upon the effects of clearing, in the discus- 

 sions of the commission appointed in 183G to examine and report upon 

 the 219th article of the Code Forestier^ 



If we cut down a belt of woodland on the sea-coast of Normandy or of Brittany 

 [says M. Arago] these countries would be opened to the west winds, coming tempered 

 from the sea, and we should have a diminution of the winter cold. If such a forest 

 was cleared on the eastern frontier of France, the cold winds from the north would 

 blow stronger, and the winters would be more severe. The destruction of a belt of 

 woodland would in these cases produce directly opposite results. 



In principle, Arago was right, but not absolutely, for, from what we 

 have said, these effects depend upon the location of the i)lace where the 

 forests are — their height, and various other causes. M. Gay-Lussac 

 held very different language : 



According to my observation np to this time, we have no positive proof that forests 

 of themselves exert an actual influence upon the climate of a large region, or upon 

 particular localities, and that, moreover, they have no influence diflerent from that of 

 other vegetation. We might inquire whether the evaporation of water is the same on 

 a naked soil as on soil covered with vegetation. These questions are so complex, 

 when considered in a climatic point of view, that their solution is very difficult, if not 

 impossible. There is another advantage that I will not deny to wooded areas, in 

 favoring the abundance of springs, and, in fact, in everything that may check the 

 quickness of flow in waters, and permit them to infiltrate slowly into the ground in- 

 stead of running off in floods, thus favoring water sources. But, still, this advantage 

 which we grant to trees, herbaceous vegetation possesses, perhaps, in higher degree, 

 the numerous close-pressed stalks and fibrous interlaced roots forming a thick and 

 spongy mat that wonderfully checks the movement of the waters and holds them till 

 they escape little by little. 



On the other hand, M. Beugnot, reporting from the commission ap- 

 pointed in 1851 to revise, if there were need, the Code Forestiere in 

 whatever related to transitory provisions of the code concerning clear- 

 ing, has denied, although with less authority than M. M. Gay-Lussac 

 and Arago, the influence that great masses of woodlands may exert 

 upon the climate of a country, as expressed in the following language 

 of his report: 



The Loire Infirieure, the Manche, the Pas-de-Calais, the Nord, the Soinme, and the 

 Maine-et-Loire are among the least wooded of the departments. Is their climate less 

 salubrious than that of the Landes, the Gironde, the Loiret, the Cher, and the Loire-et- 

 Cher, which are among the best wooded ? " We come," says M. Beugnot, " to the same 

 conclusion, in comparing the difi"erent countries of Europe, that the clearing of woods 

 is not injurious to the health of a country." 



It is impossible to solve this question without bringing proof, and in considering 

 these several opinions we will not attempt, like their authors, to make general state- 

 ments, but rather facta drawn from observatioQ, as the only means of coming to a 

 conclusion. 



' This article forbids the clearing of lands by private owners, unless their intention 

 is notiiied, at least four mouths beforehand, during which time the forest administra- 

 tion may opgose.,objections, if they find that the clearing is likely to prove a public in-. 

 jury._. (H.) 



