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‘ A is your opinion regarding the influence of forests and tree-culture upon rain- 
all? 
Are you able, from observed facts, to show that the rain-fa]ll of regions barren of 
timber may be increased by the cultivation of trees, or that rain-fall is diminished by 
the destruction of forests ? 
Will you be kind enough to refer me to any published facts bearing on this subject . 
with which you are acquainted ? 
Iam, very respectfully, 
G. W. BARNES. 
To COMMISSIONER OF AGRICULTURE. 
DEPARTMENT OF AGRICULTURE, 
Washington, April 11, 1876. 
Drar Sr: The subject of your letter is one which has occupied for the last few 
years much of the attention of scientific men; and while I have a very decided con- 
viction of my own upon which to answer your question, ‘ What is your opinion regarding 
the infiuence of forests and tree-culture upon rain-fall?” I should regret that such 
opinion should exercise any influence to retard the planting of trees or the preservation 
of existing forests, for both so greatly conduce to the interests of agriculture, mechan- 
ics, and health. The existence of a forest indubitably keeps the earth covered by it in 
a condition to receive and preserve rain-fall, and to administer it gradually to fount- 
ains and streams, whereby their supply of water remains undiminished in countries 
which are not denuded by settlement and consequent cultivation, while in densely- 
populated States, where forests have all been cut down, the earth is exposed to the sun, 
the heat, the wind, whereby its surface is made hard, and in a measure impervious to 
water, which runs off into the streams and is carried away from serving any useful pur- 
pose. My opinion is that forests do not conduce to rain-fall. 
There is, perhaps, no country that will give a stronger illustration of this subject, at 
some future day, than many of the States of this Union. Pluviometrical observations 
have been made for more than sixty years in some of the earliest-settled States, and 
within that time rain-fall has not diminished. Although this period may not be long 
enough to establish many other meteorological facts. it is but natural to suppose that 
an effect upon rain-fall by the existence of a forest, if such an effect were produced at 
all, would be more or less immediate, yet such an effect has not yet been perceived 
at all. 
It should be remarked, too, that while many of these States have been extensively 
cleared and cultivated, tree-culture has been largely attended to. And while trees 
thus planted might produce their effect upon rain-fall, if any such effect is pro- 
duced; yet they do not operate as forests do, to preserve the condition of the surface 
of the earth as reservoirs of water, to be distributed gradually to fountains and 
streams. 
I do not know of any work on this subject that contains a more exhaustive view ot 
the question, and of forestry in all its bearings, than that of Prof. George P. Marsh, 
our present minister at Rome, entitled “The Earth as Modified by the Action of Man.” 
He, after a very thorough statement and analyzation of facts, concludes that ‘We can- 
not positively affirm that the total annual quantity of rain is diminished or increased 
by the destruction of woods, though both the theoretical considerations and the bal- 
ance of testimony strongly favor the opinion that more rain falls in wooded than in 
open countries.” 
The Academy of Sciences in Vienna has issued a circular calling attention to the fact 
that for several years a diminution of water in the Danube, and other great rivers, has 
been observed, and inviting other countries to investigate and report upon any similar 
facts. A commission has been appointed in Austria for the same purpose, and the 
unanimous opinion of these scientists is said to be, that the first cause of the injurious 
decrease of water is due to the devastation of the forests. 
The truth of this opinion cannot be controverted, but it leaves the question an open 
one: Do the forests produce the water, or do they only preserve it ? 
The Garden, a weekly journal published in England, in its number of November 20, 
1&75, contains the following: ‘We have occasionally furnished facts as to the question 
ol the inflnence of forests on rain, all of which, when accurately recorded, tend to show 
the influence to be very slight at best. Walker’s Statistical Atlas states that the mag- 
nificent forests found from Minnesota to Maine have a rain-fall precisely identical with 
that of the nearly treeless prairies which extend westward from Chicago.” 
While in reply to your letter of inquiry I have expressed my own decided conviction, 
that forests do not conduce to increase the amount of rain-fall, I have shown you that. 
