20 FOREST INFLUENCES. 



INFLUENCE OF FORESTS UPON WATER AND SOIL CONDITIONS. 



(1) In consequence of deforestation evaporation from the soil is aug- 

 mented and accelerated, resulting in unfavorable conditions of soil 

 liumidity and affecting unfavorably the size and continuity of springs. 

 The influence of forest cover upon the flow of springs is due to this 

 reduced evaporation as well as to the fact that by the protecting forest 

 cover the soil is kept granular and allows more water to penetrate and 

 percolate than would otherwise. In this connection, however, it is the 

 condition of the forest floor that is of greatest importance. Where the 

 litter and humus mold is burned up, as in many if not most of our 

 mountain forests, this favorable influence is largely destroyed although 

 the trees are still standing. 



(2) Snow is held longer in the forest and its melting is retarded, giv- 

 ing longer time for filtration into the ground, which also being frozen 

 to lesser depth is more apt to be open for subterranean drainage. Al- 

 together forest conditions favor in general larger subterranean and less 

 surface drainage, yet the moss or litter of the forest floor retains a 

 large part of the precipitation and prevents its filtration to the soil, and 

 thus may diminish the supi)ly to springs. This is especially possible 

 with small precipitations. Of copious rains and large amounts of snow 

 water, quantities, greater or less, penetrate the soil, and according 

 to its nature into lower strata and to springs. This drainage is facili- 

 tated not only by the numerous channels furnished by dead and living- 

 roots, but also by the influence of the forest cover in preserving the 

 loose and porous structure of the soil. 



Although the quantity of water offered for drainage on naked soil is 

 larger, and although a large quantity is utilized by the trees in the 

 process of growth, yet the influence of the soil cover in retarding evap- 

 oration is liable to offset this loss as the soil cover is not itself dried out. 



The forest, then, even if under unfavorable topographical and soil 

 conditions (steep slopes and impermeable soils) it may not permit 

 larger quantities of Avater to drain off underground and in springs, can 

 yet influence their constancy and equable flow by preventing loss from 

 evaporation. 



(3) The surface drainage is retarded by the uneven forest floor more 

 than by any other kind of soil cover. Small precipitations are apt to 

 be prevented from running off superficially through absori^tion by thr 

 forest floor. In case of heavy rainfalls this mechanical retardation in 

 (connection with greater subterranean drainage may reduce the danger 

 from freshets by preventing the rapid collection into runs. Yet in 

 regions with steep declivities and impermeable soil such rains may 

 be shed superficially and i^roduce freshets in sjiite of the forest floor, 

 and an effect upon water conditions can exist only from the following 

 consideration. 



