THE FOREST AND SPRINGS 



379 



DEPTH OF THE SUBSOIL WATER (IN FEET) IN THE FOUR COUPLES OP 

 BORINGS IN THE STATE FOREST OF MOUDON.* 



* Totals and averages only are given in translation, condensed and rearranged from 

 results of field work extending over 28 months, May 4, 1900, to August 24, 1902. See 

 page 22 for a confirmation of these conclusions. 



strata lying horizontally and in which in consequence the subterranean sheet is 

 motionless : 



(1) The level of phreatic waters is lower under the forest at all seasons, than outside 

 of it. 



(2) The depression appears greater in regions where the rainfall is less, than where it 

 rains a great deal. 



(3) The oscillations in the level are considerably reduced and lessened by the presence 

 of the forest. 



Returning now to our subject, can we conclude from the foregoing that forests are 

 injurious to the feeding of the subterranean sheet of water on level ground in temperate 

 climates? 



This certainly seems probable. The intensity of physiological evaporation may be 

 the explanation of this curious lowering of the subterranean sheet under the woods. 

 This will be the lower, that is to say, the less thick (admitting that the impermeable 

 stratum by which the infiltrated waters are arrested, is horizontal), because the forest 

 abstracts more water from infiltration in its growth than does the neighboring 

 ground. 



Nevertheless, there is one thing which may cause us to doubt the truth of these con- 

 clusions. A careful examination of Table 6 shows us that the depression of the sheet 

 beneath the forest is more marked during the season of repose in vegetation than during 

 the summer. This fact is verified in the case of all the couples of borings, and for the 

 whole length of time during which observations were made. One might conclude from 

 this that it is not the vegetation of the trees that causes the lowering of level. 



Are we here perhaps in the presence of a fresh consequence of this fact that, under 

 the forest, the region drained of water by roots, the dry zone in fact reaches to a lower 

 level than under cultivated ground? 



However this may be, if the fact of the lowering of the level of subterranean waters 

 under the woods appears certain, its interpretation is less so, and we are left in doubt 

 as to the definite influence, all things taken into consideration of the woods upon the 

 feeding of springs in level ground. 



This first study was in the press when we received notice (March, 1904) of the official 



