DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 3869 
clearing of A would cause a combination at b which otherwise would mr. Swain. 
not occur. To argue from instances like the above against the bene- 
ficial regulating influence of forests (which perhaps the author does 
not mean to do) would seem like arguing that because it is possible 
to conceive that a man’s food may choke him, therefore food is not 
beneficial, or that the heat of the sun is not beneficial because people 
are sometimes sunstruck. 
The author’s summary of this part of the discussion is perhaps 
contained in the following sentences: “That the forest does promote 
tributary combinations, there would seem to be no question, and that 
it may therefore aggravate flood conditions necessarily follows. It is not 
contended that this increase is ever very great, but it is contended 
that forests never diminish great floods and that they probably do in- 
crease them somewhat.” 
It would seem to the writer to be nearer the truth to say that 
forests greatly diminish floods, although it is conceivable that some 
forest may slightly increase some flood at some point. 
The author further states that: “The forests are virtually auto- 
matic reservoirs, not subject to intelligent control, and act just as the 
system of reservoirs once proposed by the French Government for the 
control of floods in the River Rhéne would have acted, if built. These 
reservoirs were to have open outlets, not capable of being closed, which 
were intended to restrain only a portion of the flow. A careful study 
of their operation in certain recorded floods showed that they would 
actually have produced combinations more dangerous than would have 
occurred without them.” The last sentence of this quotation is rather 
conjectural, and its meaning is not clear, but it will be surprising to 
most engineers to be told that a reservoir not subject to intelligent 
control does not regulate, and they will hardly accept the statement. 
Of course, a lake is a more efficient regulator than a forest, for reasons 
suggested clearly by the author.* z 
The general aspect of this part of the subject seems, after all, very 
simple. The forest floor absorbs a large amount of water, prevents it 
from flowing off rapidly, and pays it out gradually into the soil, through 
which it finds its way to springs and to the underground water. If the 
land were clear of vegetation, or if it were cultivated, and especially if 
the slopes were steep, the erosion under heavy rains. would be great, 
and might leave no soil upon the rocks to serve as a reservoir in future 
storms. The author’s argument, therefore, leaves unassailed the bene- 
ficial effects of forests in regulating flow; and the illustration used by 
Mr. Pinchot seems a reasonable example of a usual phenomenon. 
The author makes a fundamental error in the very beginning of 
his discussion, which vitiates all his reasoning on this matter, when he 
illustrates the action of the forest by comparing it to the action of a 
* See page 288. 
