152 t-OREST INFLUENCES. 



cent filtration water from i^recipitation in fall, spring, and winter. '"'If, 

 therefore, be says, our earth were covered with a humus soil of 1 m. in 

 depth, subterranean drainage would be so slim that springs would be 

 scanty and continuously flowing springs absent. 



From these exi^eriments it would then be conceivable that the forest 

 floor could be of such nature as to prevent rapid filtration to the soil 

 (close uninterrupted moss carpets, or compact humus), when with sud- 

 den large masses of rain falling less water would become available for 

 underground drainage than without the forest cover. Such conditions, 

 however, are exceptional; the possibility of their occurrence, on the 

 other hand, makes it necessary in every additional case to ascertain not 

 only the nature and stratification of the soil, but also the nature of 

 the soil cover or forest floor, before we can determine whether or not 

 the presence of the forest is conducive to practically greater percolation. 



There is another element favorable to the absorption of water by the 

 soil, and to percolation and subterranean drainage, which, as far as I 

 know, has not been elsewhere noted. It is the fact that snow will lie 

 in the forest more evenly and continuously than on the unprotected 

 surface. This element of conservation not only increases the amount 

 finally remaining for drainage, but also prevents the soil from freezing, 

 keeping it open for percolation when the snows melt in spring. 



In open fields the snows are not only apt to be dissipated by ca apora- 

 tion, but the soil is more apt to become incrusted with an impermeable 

 surface stratum which would turn over the melting snow waters into 

 surface drainage. 



It is these snow waters, preserved to the subterranean draiimge, 

 which above all account for the continuity and equality of flow in 

 springs far away from the catchment basin, the waters that fell in the 

 winter and melted in the spring reai)pearing in summer. 



A further element tending to increase the amounts of subterranean 

 drainage waters lies in the retardation of the surface flow, by which 

 the time is lengthened during which the soil may take up and filter 

 through rain and snow waters. 



The forest floor offers such imi^ediments to surlace flow not only in 

 greater degree than any naked soil but than any other vegetation. An 

 advantage over other kind of vegetation is also found in the deep i)ene- 

 tration of the roots of trees, which increases the chance for perc(jlation, 

 while the more compact soil cover of a green sward would be rather 

 opposing percolation. All that has been said regarding evaporation 

 and transpiration within and without the forest needs also be kept in 

 mind in the discussion of the amounts of drain waters for underground 

 disposal. 



The conclusion, then, is, that in general a forest floor, although retain- 

 ing much of tlie water in its upper strata, allows less water to run off 

 superficially, and by rendering the soil more permeable larger amounts 

 of water are turned into subterranean channels. 



