22 THE ROLE OF FORESTS 



where. The level is lower under a mature stand than in young growth, 

 the differences being greater in a dry than in a wet climate. Where there 

 is a great deal of rainfall the difference may not exceed 9 or 10 inches. 

 Henry's observations at Nancy (see Appendix, p. 379) confirmed these 

 conclusions (about 1 foot difference) and De Lapasse now cites proof on a 

 large scale. It was already proved that surface water in the Landes and 

 Gironde had dried up, after extensive areas had been sown, planted, and 

 drained, in the Nineteenth Century, but it was not until 1917 that proof 

 was secured that if these forests were cut the water level would rise again. 

 This has now been proved in the forests of Porge (Gironde) where 8,649 

 acres were clear-cut during the period from 1904 to 1911; where 5,436 

 acres were clear-cut in the forest of Solferino (Landes) during the period 

 from 1905 to 1911; and where 1,236 acres were clear-cut in the forest of 

 Soulac. In the latter case the timber was 65 years old; the felling began 

 in 1912 and was finished in 1914. According to accurate data secured by 

 Conservateur de Lapasse the former water level at Soulac was 3.3 feet 

 below the floor of the local church. At the end of 1916 the water began 

 to flood the chapels to the depth of 2 inches and on January 6, 1917, the 

 water flooded the central nave and the church itself to a depth of 6 inches 

 and the chapels to a depth of 19 inches. In the same locality (Soulac) u 

 the water level of the wells rose 27| inches; the local hotel cellars, for- 

 merly dry, had standing water to a depth of 8 inches. According to de 

 Lapasse this is proof positive that clear cutting these mature pine forests 

 has materially raised the water level. Such a conclusion is of immense 

 importance in connection with drainage problems. 



Springs. 12 According to Huffel, ground in a forest is better watered 

 from the atmosphere than are the bordering plains. This difference is 

 greater in winter than in summer may be 20 per cent more. In the 

 mountains forests unquestionably diminish run-off and bring about a 

 greater infiltration of water which may ultimately feed springs. This is 

 due not only to the obstacles which trees, roots, and litter present to 

 prevent run-off, but also to the greater porosity of the forest soil and to 

 the fact that snow melts slower under forest cover. Both French and 

 Russian experiments have proved, however, that the water level in the 

 forest on level ground is about one foot lower than in the fields. On the 

 other hand, the variation in water level is less in the forest ; the infiltra- 

 tion is slower; in other words, the forest is a regulator of water levels (as 

 with temperature). Huffel concludes that forests increase precipitation, 

 retain a part of the rainfall on branches and return it to the air directly, 



11 L'Influence de la Foret sur le Regime des Eaux a Soulac, pp. 1-8, M. de Lapasse, 

 1917. 



12 See Appendix, p. 361, for a more detailed discussion of this subject, as presented by 

 Huffel. 



