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



masses of air saturated with vapor in motion, which does not fail to 

 turn to raiu when they are raised, crowded as they are by the obstacle. 



3. From the humidity that commonly prevails in the interior, and 

 near the woods, which leads to the precipitation of dew, when the tem- 

 perature is lowered. 



The transformation of cleared lands into marshes is real. We will 

 cite examples not in Asia Minor, as has been done, but in France. When 

 the trees are cut, the roots die, and the soil becomes compact. La 

 Brenue, situated between the Indre and the Creuse, presents a circular 

 area of over 200 kilometers in circumference, or about 80,000 hectares. 

 The soil of that region is argillo-siliceous, resting upon an impervious 

 bed of clay, of more or less thickness, which opposes the infiltration of 

 the waters. It is covered with ponds, to which are attributed the inter- 

 mittent fevers to which the population are a prey. This region was 

 covered ten or twelve centuries ago with forests, interspersed with 

 meadows watered with living waters, and there then existed neither 

 ponds nor marshy grounds, and it was renowned for its fertility, its 

 pasturages, and the sweetness of its climate. On the clearing of of these 

 woodlands the ponds succeeded, and the lands speedily became unpro- 

 ductive and valueless. Their increase had come to such a point that, in 

 1714, Bourbet-en-Brenne counted but 309. 



The same thing was seen in the Sologue, which represents an area of 

 450,000 hectares, and of which the insalubrity is proverbial ; but this deplo- 

 rable condition did not always exist. Historical documents show that 

 a great part of this country was formerly wooded. Upon clearing, fol- 

 lowed the disappearance of the waters, wastes, and insalubrity. Now a 

 clearing might not bring a like condition of things, since we have means, 

 by means of drainage, of rendering fertile marshy lands that have been 

 in this condition for many years. 



In the effects produced in mountains, we are to notice the influence 

 of roots which favor the infiltration of rain-waters, and feed the springs. 

 In such a country, clearing leads promptly to the formation of torrents, 

 of which the Alps present numerous examples. 



The effect, when the slopes covered with detritus of rocks are crowned 

 with vegetation in vigorous growth is, that the roots strongly interlac- 

 ing form a net-work, and we see it rapidly disappear when the firs and 

 larches on the flanks of the mountains are removed. We see that when 

 inconsiderate cuttings are made on these slopes that the waters flowing 

 there, carry down the vegetable soil, and a ravine is soon formed. This 

 ravine enlarges, and becomes in time the bed of a torrent, while nothing 

 of this is seen where the forests remain untouched. The whole eastern 

 part of the department of the Hautes-Alps presents numerous efiects of 

 this kind. 



We see, therefore, that the presence of a forest upon the soil, strongly 

 inclined, opposes the formation of torrents, while clearing delivers the 

 soil to this destruction. It is easy to explain the effect that follows as 

 soon as the soil is again covered with vegetation, first of low plants, 

 then with trees, as we have said, forming a kind of net-work that gives 

 it consistence while the branches and leaves break the force of the 

 storms. The trunks, shoots, and brush oppose multiplied resistances to 

 the currents that would otherwise erode the soil. The effect of vegeta- 

 tion is therefore to give greater solidity to the soil over its whole sur- 

 face, and prevent it from being carried into the channel-ways, as would 

 otherwise happen. The soil, when opened by the roots, and covered 

 with a spongy humus, absorbs a part of the waters, that, being hindered 

 from running off upon the surface, sink into the interior and become a 



