198 REPORT OF THE FORESTRY COMMITTEE 



(1) Constitutes an effective means of draining and drying up swampy lands, 

 the breeding places of malaria and swamp fevers. The reforesation of the 

 Landes, Sologne, the Pontine marshes, and a hundred other examples prove this. 



(3) Draws moisture from a greater depth than does any other plant or- 

 ganism, thus affecting the unutilized water of the lower horizontal stratk by bring- 

 ing it again into the general circulation of water in the atmosphere, and making it 

 available for vegetation. 



(3) Lowers to some extent the subterranean water level, but it has no 

 injurious effect upon springs, since these are practically lacking in the level coun- 

 tries with horizontal geological strata where its lowering influence has been chiefly 

 noted. 



(4) Refreshes the air above it and increases the condensation of moisture 

 carried by the winds, thus increasing the frequency of rains during the vegetative 

 season. 



In hilly and mountainous country forests are conservers of water for stream- 

 flow. Bven on the steeper slopes they create conditions with regard to surface 

 run-off such as obtain in a level country. Irrespective of species they save a 

 greater amount of precipitation for streamflow than does any other vegetable 

 cover similarly situated. They increase underground seepage of water to a 

 larger extent than does any other vegetable cover. The steeper the slope the less 

 permeable the soil, and the heavier the precipitation the greater its effect. 



In the mountains, the forests break the violence of rain, retard the melting of 

 snow, increase the absorptive capacity of the soil cover, prevent erosion, and 

 check surface runoff in general, thus increasing the underground seepage and 

 and so tend to maintain a steady flow of water in streams. 



In the mountains the greatest source of loss of precipitation is through sur- 

 face run-off, and the most important influence which a forest cover has is in 

 reducing this. In general it may be stated that the amount of water which the 

 forest cover saves to the soil by reducing the surface run-off and changing it to 

 underground seepage is as follows : For forests at low altitudes where the rains 

 are not heavy and the soil is less subject to freezing, 20 per cent ; for forests of 

 moderate altitudes, 35 per cent, and for mountain forests, 50 per cent of the pre- 

 cipitation. The saving of precipitation effected in this way by the forest is more 

 than sufficient to offset whatever loss may be "sustained through transpiration or 

 interception by tree crowns. This is clearly brought out by the following facts : 

 The entire loss of water from forested areas at moderate altitudes, even on the 

 steepest slopes, is about equal to that from forest in level country. Ney places this 

 at 19.4 inches, or 61.5 per cent of the precipitation (31.5 inches). Cultivated 

 fields on similar slopes have been computed to lose, through interception by vege- 

 table cover, evaporation from the soil, transpiration, and surface run-off, 24.9 

 inches, or 79 per cent of the precipitation, and bare surfaces 27.2 inches, or 86.4 

 per cent. The higher the altitude, the steeper the slope, the heavier the rainfall, 

 and the greater the precipitation, the more marked will be the difference. This 

 holds true, not only for such species of trees as beech or pine, the entire loss of 

 water from which is less than that from cultivated fields, but also for spruce. 



