230 



AMERICAN FORESTRY 



it would be necessary to have the same 

 area under identical conditions except 

 that at one time it should be foresteJ 

 and at another time it should be defor- 

 ested ; this condition is manifestly im- 

 possible of attainment ; it never has 

 been attained and it never will be. In 

 the published comparisons which are 

 found in various papers dealing with 

 the subject, the conditions are never the 

 same. A curious fact, however, is that 

 Professor Moore and some other 

 writers should not think it even neces- 

 sary to make any statement as to the 

 proportion of given area under discus- 

 sion which is covered by forests. Pro- 

 fessor Moore thinks he shows that the 

 floods in the Ohio River have not 'in- 

 creased, but he does not even tell us 

 and does not seem to think it necessary 

 to inquire whether the total forested 

 area has increased ' or decreased and 

 how much. He reasons entirely from 

 one premise. He says : "The floods 

 have not increased, I do not know defi- 

 nitely about the forests, therefore the 

 forests have no effect on floods." 



Now while there has been great cut- 

 ting on the mountain slopes during the 

 past decade or two, it is very possible 

 that some other slopes which had been 

 cut previously have been growing up, 

 and the total forested area may have 

 changed but little. Certainly no con- 

 clusion worthy of credence can be 

 drawn until this point is investigated. 



Statistical reasoning, therefore, is un- 

 satisfactory in this case as it is in con- 

 nection with rainfall, and we must 

 therefore resort to deductive reasoning 

 based on simple fundamental principles ; 

 and here again there are two principles 

 which every observing man knows to 

 be true and which no amount of spe- 

 cious reasoning like that of Professor 

 Moore will suffice to counteract. 



These are, first, that the forest re- 

 tards the discharge of water from the 

 surface of the ground. The forest 

 causes a million dams, which obstruct 

 the surface water and cause it to trickle 

 along slowly; it also forms a bed of 

 humus which is able to absorb this 

 water: beneath which is a porous 

 ground which can carry it still deeper 



When a sudden downpour comes, not 

 only do the forest trees intercept a por- 

 tion of rain on their leaves and branches 

 and allow it to trickle gradually down 

 the trunk or drip to the ground, but the 

 water, when it reaches the ground, is 

 obstructed and has time to sink in, and 

 finds something to sink into. On the 

 open ground, on the contrary, on steep 

 slopes (and it is only these that we refer 

 to) a sudden downpour causes the 

 water to be discharged quickly over the 

 surface into the streams. If the forest 

 then, as every reasonable man knows 

 is the case, retards the surface run-off, it 

 must, on the whole, diminish the vio- 

 lence of freshets. 



The second fact of importance is that 

 the forest retards the melting of the 

 snow ; everybody familiar with the 

 country knows that in the forest the 

 snow iasts considerably longer than it 

 does in the open, although there may 

 be isolated drifts in the open where cer- 

 tain beds of snow may linger longer 

 than the snow in the forest. On the 

 whole, and speaking generally, forests 

 retard the melting of snow, and there- 

 fore every reasonable man will conclude 

 that they must, on the whole, by caus- 

 ing the snows to be discharged in a 

 longer time into the streams, reduce on 

 the average, the floods. Moreover, by 

 facilitating the percolation into the 

 ground and the subsequent slow giving 

 out of the percolated water by springs 

 and seepage, the forests must, on the 

 whole, maintain a higher low-water 

 flow in the streams. 



Professor Moore's arguments on this 

 point if they may be called argu- 

 mentsare in part faulty and in part 

 based on a misconception of the ques- 

 tion, as will now be shown. 



In the first place, the sum and sub- 

 stance of his claim is that forests do not 

 decrease the extreme floods or increase 

 the ex 't '-erne low-water flow. This has 

 long been admitted by competent hy- 

 drolo.gists. It is even possible to con- 

 ceive circumstances under which the 

 presence of a forest might increase the 

 flood which, if the forest were not there, 

 would come from a given area. But 

 the navigability of streams, the forma- 



