328 M. BECQUEREL, ON THE CLIMATIC EFFECTS OF FORESTS. 



It will not sufiBce to study the calorific efiects of clearing upon cli- 

 mates. We must seek to ascertain the action they exert upon springs, 

 and the physical effects they produce in mountainous regions upon a 

 denuded soil, as well as the effects that follow clearing upon soils of wet 

 clay. 



VVe will here make an observation that is not without some impor- 

 tance. We have seen above that a tree becomes warm or cool like any 

 inorganic body, and that in proportion as the leaves become cool by 

 night from nocturnal radiation, this loss is repaired by heat radiated 

 from the trunk and branches. This condition of things, which has not 

 heretofore been pointed out by physicists, hinders the air from cooling, as 

 much as if this radiation from the trees had not taken place. The eflect 

 of woods in cooling the air is not as great as has been supposed, and 

 the condition of the soil, moreover, modifies this inHuence in a singular 

 degree. 



On the effects of clearing upon springs and water-courses. 



The effects of clearing upon springs, and the amount of living waters 

 that flow through a country are most important points for consideration, 

 and require serious attention. The difiiculties in recognizing these 

 effects are the greater when we are unable to say a priori whether a 

 forest or a part of a forest supplies any particular spring or river. 



Springs are in general due to infiltrations of rain water into a per- 

 vious soil, which it traverses until meeting an impervious stratum, over 

 which it flows when inclined, until it comes to the surface, forming 

 rivulets, streams, or other running waters. The water in wells has no 

 other origin. Great springs are commonly found in the mountains. 

 Forests contribute to their formation, both from the humidity of the 

 soil that they produce, and the obstacles which they oppose to evapora- 

 tion from the surface. Besides this, the roots of the trees, in separating 

 the soil, render it more pervious, and thus facilitate infiltration. We cite 

 in the memoir, a certain number of characteristic examples, but will 

 here refer to but three of the most remarkable : 



Strabo informs us, that it was necessary to take great precautions to 

 prevent Babylon from being washed away by the waters. The Euphrates, 

 be says, began to swell at the beginning of spring as soon as the snows 

 began to melt in the mountains of Armenia, and filled the banks at 

 the beginning of summer, necessarily forming vast masses of water, 

 which would inundate the cultivated fields if not diverted by means of 

 ditches and canals, and that when these canals were full, the waters 

 spread over the plains like the Nile. This state of things no longer 

 exists, and M. Oppert, who traveled through Babylonia some years 

 since, relates that the mass of waters transported by the Euphrates is 

 much less than it was ages ago; the filling of the banks no longer 

 occurs, the canals. are dry, the marshes become dry during the powerful 

 heats of summer, and that the country has ceased to be insalubrious. 

 This disappearance of the waters he assures us ought to be ascribed to 

 the clearing off' of forests on the mountains of Armenia. 



These effects are incontestable, although there have been some per- 

 sons who denied them. The examples that I am about to present fur- 

 nish proofs much more forcible, because they are derived from observa- 

 tions that inspire confidence. 



De Saussure^ notices the diminution of waters in the Swiss lakes as a 

 result of clearing, especially in Lakes Morat, Neufchatel, and Bienne. 



» Voyage dans hs Alpes, ii, chap. xvi. 



