H. FOREST INFLUENCES. 



[Condensed from Bulletin 7, Forest Influences, pp 191, 1893, with additional notes.] 



One of tlie arguments upon which a change of policy in regard to our forests, and especially 

 on the part of the National Government, is demanded, refers to the influence which it is claimed 

 forest areas exert upon climate and water flow. It is argued that the wholesale removal and 

 devastation of forests affects climate and water flow unfavorably. 



Popular writers on forestry, friends of forestry reform, and the public mind have readily taken 

 hold of this proposition, enlarged upon it, and generalized without sufficient and relevant premises, 

 and before it was possible for science and systematic observations to furnish grounds or sound 

 deductions; hence we have had only presumptions supported by superficial reasoning and occa- 

 sional experiences. Even scientific writers have discussed the question without proper bases, and 

 have sought to reason out the existence or absence of such an influence upon general premises 

 and such evidence as the history of the world seemed to furnish, or else upon observations which 

 were either of too short duration to allow elimination of other disturbing factors or else were 

 otherwise unreliable. 



From the complication of causes which produce climatic conditions it has always been difficult 

 to prove, when changes of these conditions in a given region were observed, that they are perma- 

 nent and not due merely to the general peiiodic variations which have been noted in all climates 

 of the earth, or that they are due to a change of forest conditions and to no other causes; hence 

 some climatologists have thought proper to deny such influences entirely. On the other hand 

 there are as trustworthy and careful observers who maintain the existence of such influences; 

 but only of late has the question been removed from the battlefield of opinions, scientific and 

 unscientific, to the field of experiment and scientific research, and from the field of mere specu- 

 lation to that of exact deduction. But the crop of incontrovertible facts is still scanty, and 

 further cultivation will be necessary to gather a fuller harvest and then to set clear the many 

 complicated questions connected with this inquiry. 



Meanwhile a thorough beginning with a view to settle the question by scientific methods and 

 careful systematic measurements and observations has been made in Europe, where the existence 

 of well-established forest administrations, manned with trained observers, has rendered practicable 

 the institution of such work on an extensive scale— the only one which can yield adequate results. 

 Nevertheless, the results of these experiments, cited below, have so far failed to advance materially 

 our positive knowledge regarding the relation of forest growth and meteorological phenomena. 



The reason for this failure is to be sought, first, in the complexity of the problem, which ren- 

 ders any experimentation difficult, and, secondly, in the deficiency in appliances and methods of 

 meteorological observations. 



Not only is it difficult to analyze or control the various causes that may influence climatic 

 variations from year to year, but we are not yet prepared to determine the uniformity of the local 

 distribution of meteorological phenomena or of the measurements of the same by our instruments. 



Hence some of the small, though well defined differences in rainfall and temperature observed 

 over forest and open country in earlier experiments may be attributed to the nonconformity of the 

 natural local distribution of these phenomena or to lack of uniformity in instruments and methods. 



It may be proper to call attention to and accentuate the fact that the question of practical 

 importance is not so much as to the effects upon the general climate, but as to the local modification 

 of climatic conditions which a forest area may produce. 

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