FORESTS, RESERVOIRS, AND STREAM FLOW 267 
So, likewise, it is held that forests are necessary to protect mountain 
slopes because of the greater precipitation prevailing there; yet the 
forests are said to increase this precipitation materially. 
There is really very little, theoretically, to support the claim that 
forests increase precipitation. It is said that the cooler status of forest 
areas condenses moisture and induces precipitation; but if this were so 
in midsummer, when the least precipitation falls, how about the rest 
of the year when no such difference exists, but the reverse, if anything? 
Take, for example, the great forests around the source of the Yellow- 
stone. During the period when the bulk of the precipitation falls, 
the temperature of the forests cannot differ materially from the out- 
side, and it is impossible to believe that the forest exercises much 
influence upon the snowfall. 
The fact that these high areas are generally wooded is frequently 
cited to prove that forests produce the higher rates of precipitation 
which also prevail there. But would it not be more reasonable to say 
that the forests flourish there because of the higher precipitation, and 
that the latter is due to the elevated situation and consequent lower 
temperature? Is not this, in fact, the reason why precipitation is 
nearly always greater upon the hills than upon the neighboring low- 
land? The mountains are Nature’s wine-press by which she extracts 
from an unwilling atmosphere the elixir of life for the hillsides and 
the valleys below, and she does this whether the forests have been cut 
away or not. 
In one respect, and a very important one, forests diminish pre- 
cipitation, and that is in the deposition of dew. Dew is essentially 
an open-country phenomenon, where the radiation of heat from the 
earth’s surface is unobstructed. Clouds or high cover of any kind, 
and also wind, interfere with this process and prevent the dew from 
gathering. It collects in full strength on low shrubbery, to a less 
degree on small trees, as in orchards, and penetrates for short dis- 
tances under forest cover. In the heart of the native forest of full- 
grown timber, however, dew is practically unknown. The quantity 
deposited in the open country in a single night is quite large under 
dry up, the rivers will cease to run, the rain will fall no more, and America will be 
a desert!’ Considering how large a percentage of our forests has already disap- 
peared, the extraordinary rains in all parts of the United States during the past 
year are not exactly in line with this dismal prophecy. If one were to judge from 
the records of the past few years only, he must conclude that deforestation is 
increasing rainfall. 
