492 



CONSERVATION 



not rest upon an impervious surface. 

 The forest and its cover prevent the 

 earth beneath from being baked by the 

 sun and compacted by the rain. It is 

 kept in a porous condition ready to ab- 

 sorb water which filters down to it 

 through the forest cover. Any conclu- 

 sion, therefore, drawn from Colonel 

 Chittenden's simile nmst be inaccurate. 



The author's summary of this part of 

 the discussion is perhaps contained in 

 the following sentence: "That the for- 

 est does promote tributary combina- 

 tions, there would seem to be no ques- 

 tion, and that it may therefore aggra- 

 vate flood conditions necessarily follows. 

 It is not contended that this increase 

 is ever very great, but it is contended 

 that forests never diminish great floods 

 and that they probably do increase them 

 somewhat." 



It would seem to be much nearer the 

 truth to say that forests generally di- 

 minish floods, although it is conceivable 

 that a forest may slightly increase a 

 given flood at some points. 



The author further states that "the 

 forests are virtually automatic reser- 

 voirs, not subject to intelligent control, 

 and act just as the system of reservoirs 

 once proposed by the French govern- 

 ment for the control of the floods of 

 the River Rhone would have acted if 

 built. These reservoirs were to have 

 open outlets, not capable of being 

 closed, which were intended to restrain 

 only a portion of the flow. A careful 

 study of their operation in certain re- 

 corded floods showed that they would 

 actually have produced conditions more 

 dangerous than would have occurred 

 without them." 



The last sentence of this quotations is 

 rather conjectural and its meaning is 

 not quite clear, but it will be surpris- 

 ing to most people to be told that a res- 

 ervoir not subject to intelligent control 

 does not regulate, and they will hardly 

 accept the statement. Of course, a lake 

 is a more efficient regulator than a for- 

 est, because, if its level is rising, the 

 discharge from its lower end is always 

 less than the flow into its upper end, 

 while in case of the forest, when its 

 storage is exceeded, its level cannot rise. 



and it can simply hinder the discharge 

 of later rain-water by physically ob- 

 structing its flow^ 



The general aspect of this part of the 

 subject seems, after all, quite simple. 

 The forest floor absorbs a large amount 

 of water, prevents it from flowing ofif 

 rapidly, and allows it to gradually per- 

 colate into the porous ground beneath. 

 If the land were clear of vegetation, or 

 if it were cultivated, and especially if 

 the slopes were steep, the erosion would 

 be greater, and might sooner or later 

 leave no soil upon the rocks to serve 

 as a reservoir in future storms. The 

 author's argument, therefore, leaves un- 

 assailed the beneficial efifects of forests 

 in regulating flow. 



The fact must be emphasized that 

 those who believe in the beneficial effect 

 of forests upon flow do not urge the 

 preservation of the forests on lands 

 needed for agriculture. The beneficial 

 efifects of the forests on flat lands in 

 modifying the violence of freshets and 

 increasing the low-water flow is much 

 less clear than in the case of forests in 

 steep mountain regions. It is the pres- 

 ervation of these last — forests upon 

 land not suited to agriculture — that is 

 believed to be especially important from 

 every point of view. 



The statement of Colonel Chittenden 

 that the flood of 1908 in the Western 

 States would have been much greater if 

 the region had been forested, is a mere 

 statement of his own opinion, entirely 

 without proof, and undoubtedly inca- 

 pable of proof; and, further, if the 

 gauge records given by him show that 

 it is impossible to find evidence in them 

 to support the current theory of forest 

 influence, it may also be stated that 

 there is nothing in them to support his 

 own contention. 



The question will, of course, have 

 occurred to the reader of these re- 

 marks : Why it is not possible by long- 

 continued observations of the height of 

 floods on our rivers to settle this ques- 

 tion absolutely ? With reference to this 

 some explanation is necessary. The 

 flow of a stream is the resultant of a 

 number of elements, chief among which 

 are rainfall, its distribution throughout 



