Mr. Pinchot, 
158 DISCUSSION : FORESTS, RESERVOIRS, AND STREAM FLOW 
explained the function of the forest and the purpose of his illustration 
as follows: : 
“The effect of a forest on a steep slope is to cover that slope with 
leaves, rotten and half-rotten sticks, and other mechanical obstruc- 
tions which prevent the water which falls upon that slope from run- 
ning straight down below as rapidly as it would otherwise. In this 
connection it has, in the second place, the effect of permitting the 
water which falls on that slope, instead of rushing off rapidly, to sink 
into the mountains. 
“Now the mountains are substantially great reservoirs of water, 
which cannot operate unless they are renewed from time to time by 
the rain that falls upon them; and the rain that falls upon them can- 
not get into the mountain reservoirs unless the surface of these reser- 
voirs is in an absorbent condition. I can illustrate that to the 
members of the committee in a moment with.a glass of water and a 
piece of blotting paper, as a definite illustration.” ; 
The illustration quoted above then follows. 
Unfortunately, Colonel Chittenden has failed to gather from these 
statements what seems to the speaker to be their obvious meaning. 
The illustration used is a fair description of one, but only one, of 
the essential functions of the forest floor, and due notice was given 
to that effect. The forest floor offers a physical obstruction to the 
rapid escape of water over the surface, and thus itself provides to 
some extent a small storage reservoir. Colonel Chittenden admits 
this influence for average conditions; indeed, it is a matter of such 
common observation as to be indisputable. The practical value of 
this influence may be little or much, depending on the character and 
amount of precipitation and the thickness of the undergrowth, decay- 
ing litter and humus on the ground. 
There is, however, another function of the forest floor which in 
practical value far surpasses this one. The forest floor acts on the 
soil itself to multiply its absorptive capacity. The humus, which by 
natural action is being constantly mixed with the upper layers of 
mineral soil, greatly increases its receptive and retentive power, while 
the deep-penetrating.roots also open passages through which water 
readily passes into the great reservoir of ground-water. 
That Colonel Chittenden has failed, however, to consider this 
function is evident throughout his discussion. In giving an illustra- 
tion, he says:* “Consider an inclined-plane surface, practically im- 
pervious to water.” When it is understood that under the forest the 
surface is very far from impervious, and that, on the contrary, it is 
absorbent in a high degree, the argument is seen to be fallacious. 
Failing to note this function of the forest floor, Colonel Chittenden 
misses entirely the greatest influence which the forest exerts on fallen 
moisture—that of changing surface drainage to underground drainage, 
* Page 247, 
