46 FOBEST LANDS FOB THE PBOTECTION OF WATEBSHEDS. 



ground and the leaves and whatever may be on the surface and is 

 evaporated, and the third part percolates into the ground and either 

 descends until it gets to the ground water and is given out in springs 

 or part of it is taken up by plants and used by them in building up 

 their tissues and part of it again is evaporated through their leaves. 

 The preservation of the flow of the streams depends mainly on keep- 

 ing the percolation of the water into the ground at the expense of 

 what flows directly from the surface. That we can reduce, but later, 

 of course, it percolates into the ground, then the flow will be dimin- 

 ished and the springs will be held up in the dry season of the year. 

 That is what the forest does. The forest bed or floor absorbs the 

 water as it come down and gives it out gradually, and I think a mis- 

 apprehension, perhaps, exists in regard to the simile which has been 

 made to a sponge, and in that paper which the chairman had that 

 mistake is made fundamentally. 



The forest floor is not like a sponge or a-n impervious surface. It 

 does not simply intercept the water which flows down that impervious 

 surface and filter it as it passes through it and give it out gradually 

 below. The real sponge, the real reservoir, is the soil underneath 

 the bed of the forest humus, and this bed holds the water and allows 

 it to gradually percolate or flow into the soil. A distinction must 

 be made, and a rather sharp one, between the action of forests where 

 the land is flat and where the land is steep. Where the land is flat 

 the most important elements are the evaporation and the percola- 

 tion; if the land is absolutely flat there would be no tendency for 

 the water to run off ; but where the ground is steep there the action 

 of the forest is the most important, and there its action is two- 

 fold. As I said, it retards the delivery into the the streams of the 

 water which ultimately reaches those streams; it holds the water 

 and delivers it gradually to the ground beneath. It is also a great 

 factor during the winter and spring in retarding snow. The snow 

 which falls in the forest stays there much longer than the snow which 

 falls in the open, and it is melted gradually, and therefore is deliv- 

 ered gradually to the streams and fills them up more gradually than if 

 it went off all at once. There are other ways besides these agencies of 

 increasing the percolation. One is cultivation, where the surface of 

 the ground is plowed up; that increases the percolation and allows 

 the streams to be fed, to a certain extent, during the growing season, 

 and on steep slopes, which ought not to be cultivated, or can not be 

 cultivated, the forest is practically the only agency which is useful 

 in conserving this flow of the stream. The flow from the forest, 

 then, is delivered gradually to the streams. It feeds the springs, 

 keeps up the slow water flow, prevents the water from going off sud- 

 denly into the streams, and, furthermore, prevents the erosion, 

 because the soil is not carried away by the flowing water. Therefore 

 the relation between the forest and the floods is a perfect and neces- 

 sary one, and the opinion of engineers, scientists, and geologists all 

 over the world is overwhelmingly in favor of that influence. 



As the chairman has undoubtedly seen in the South, if anything 

 absorbs the flow from a cultivated area the water flowing from the 

 steep slopes carries down the soil, and the rush of water obstructs the 

 flow below. Of course, the silt which comes from the mountain is 

 deposited in the first pool. The water takes up the silt according to 



