416 FORESTS AND THEIR CLIMATIC INFLUENCE 



hectares, (197,080 acres.) The soil of this country, which is argilo-sili- 

 ceons, rests on a substratum of impenetrable clay which resists the infil- 

 tration of water; it is thickly covered with pools, to which are attributed 

 the intermittent fevers prevalent throughout the district. Ten or twelve 

 centuries ago it was occupied by forests interspersed with meadows, 

 watered by i-unning streams and fountains, and there existed then neither 

 pools nor swamps; on the contrary, it was renowned for the fertility of 

 its pastures and the amenity of its climate. The disappearance of the 

 forests was succeeded by collections of stagnant water wliich took i)os- 

 session of the now unproductive and worthless soil, and this to sucli an 

 extent that in 1714, the tract of Bouchat-en-Breune alone counted no 

 less than one hundred and nine of them. (Piganiol de la Force, Descrip- 

 tion de la France.) A like state of things appears in Sologne, wliich rep- 

 resents a surface of 450,000 hectares, (l,ll!i,000 acres,) and which has 

 become proverbial for its insalubrity. The deplorable condition in which 

 we see it did not always exist. Historical documents show that a great 

 part of this country was of old clothed with woods. Their extirpation 

 has been succeeded by accumulations of water, fens, and the attendant 

 nmlad^.es. At the present day the removal of the forest need not involve 

 so calamitous a consequence, for modern ingenuity has placed at our 

 disposal the means of restoring salubrity and fertility to swamps and 

 moor lands of even long standing. 



The effects produced in mountains clearly evince the action of roots 

 in promoting the infiltration of rain-water and the alimentation of 

 sources. In a mountainous country the extirpation of forests promptly 

 leads to the formation of torrents. Of this the Alps furnish numerous 

 examples. When, in fact, vegetation is left to develop itself freely on 

 the sides of mountains covered with the detritus of rocks from the sum- 

 mit, dense forests of spruce and larch quickly occupy their flanks, and 

 the interlacing roots form a net- work which binds and protects the soil. 

 If clearings are inconsiderately made in the direction of the slopes the 

 waters follow the course of the openings, and, carrying with them the 

 vegetable deposit, rapidly excavate furrows. These furrows extend with 

 time, and end by forming torrents. Nothing of this sort occurs where 

 the woods have not been felled. All the eastern part of the department 

 of the Hautes-Alpes presents numerous results of this kind. 



We thus see that the presence of a forest on a surface of steep inclin- 

 ation counteracts the formation of torrents, while disboscation exposes 

 the soil to their ravages. This effect it is easy to explain when the soil 

 is once occupied by vegetation, first by the humbler plants, then by 

 trees whose roots, forming a sort of feltij^g, give consistence to the 

 ground at the same time that the branches and leaves break the force of 

 heavy rains. The trunks, the offshoots, the brush-wood, multiply ob- 

 stacles in the way of the currents which would otherwise furrow the 

 earth. The etfect of vegetation, therefore, is to give more stability to 

 the soil and to distribute the waters over its whole surface, so as to pre- 

 vent their following the drains in a mass, as would be the case if the 

 earth were denuded. The soil, being divided by the roots and covered ivltli 

 a])orous humus, absorbs a part of the waters which cease to flow down 

 the slopes and are conveyed by percolation to the low grounds, where 

 they serve to feed streams and fountains. Such are the benefits resulting 

 from the presence of forests on mountains and inclined surfaces exxjosed 

 to torrential rains. 



