FORESTS, RESERVOIRS, AND STREAM FLOW 281 
streams, and may, and often does, bring the accumulated waters of a 
series of storms in one part of the water-shed upon those of another 
which may occur several days later; so that, not only does the forest 
at such times exert no restraining effect upon floods, but, by virtue of 
its uncontrolled reservoir action, may actually intensify them. 
(8) In periods of extreme summer heat forests operate to diminish 
the run-off, because they absorb almost completely and give off in 
evaporation ordinary showers which, in the open country, produce a 
considerable temporary increase in the streams; and therefore, while 
small springs and rivulets may dry up more than formerly, this is 
not true of the larger rivers. 
(4) The effect of forests upon the run-off resulting from snow- 
melting is to concentrate it into brief periods and thereby increase 
the severity of freshets. This results (a) from the prevention of the 
formation of drifts, and (b) from the prevention of snow-melting by 
sun action in the spring, and the retention of the snow blanket until 
the arrival of hot weather. 
(5) Soil erosion does not result from forest cutting in itself, but 
from cultivation, using that term in a broad sense. The question of 
preventing such erosion or soil wash is altogether one of dispensing 
with cultivation or properly controlling it. The natural growth which 
always follows the destruction of a forest is fully as effective in pre- 
venting erosion, and even in retaining run-off, as the natural forest. 
(6) As a general proposition, climate, and particularly precipita- 
tion, have not been appreciably modified by the progress of settlement 
and the consequent clearing of land, and there is no sufficient reason, 
theoretically, why such a result should ensue. 
(7) The percentage of annual run-off to rainfall has been slightly 
increased by deforestation and cultivation. 
If the foregoing propositions are correct they enforce two very 
important conclusions—one relating to the regulation of our rivers 
and the other to forestry. 
It follows that no aid is to be expected in the control or utiliza- 
tion of our rivers, either for flood prevention, navigation or water 
power, by any practicable application of forestry. Remember always 
that it is the extreme of flow, not the medium condition, that controls 
the cost of river regulation. It is the floods and low waters that 
measure the cost. Any scheme of control that is not based upon these 
