232 



AMERICAN FORESTRY 



national Congress of Navigation held 

 at Milan in 1905. Professor Moore 

 says that Mr. Lauda's conclusions are 

 "that progressive deforestation of the 

 country has had no effect in increasing 

 floods nor in augmenting their height." 

 Let us read Mr. Lauda's conclusions 

 as presented at the Congress in Milan. 

 He says :* "If now the final judgment 

 on the subject of the influence of forests 

 on the regimen of streams be unfavor- 

 able to the forest to this extent, that 

 there are denied to it certain of the 

 properties attributed to it generally, 

 it does not follow from this that it is 

 necessary to oppose the re-wooding of 

 arid surfaces, the replanting of the 

 basins of streams, or the maintenance 

 of plantations of trees. The general 

 utility of the forest is so well settled, the 

 extraordinary appreciation in which it 

 is held, as a means of protecting the soil 

 against landslides, is so firmly estab- 

 lished, its great advantageousness, es- 

 pecially for the spring district, in hold- 

 ing back earth thrusts and reducing the 

 amount of sediment carried by rivers so 

 important, that these reasons alone jus- 

 tify fully the greatest possible promo- 

 tion of forest culture." 



Any fair discussion would have in- 

 cluded this reference. 



Professor Moore, referring to this 

 Congress says: "The writers heartily 

 favor the protection of the forests and 

 their cultivation" but "they were unani- 

 mous in the opinion that forests exer- 

 cise little influence upon either the high 

 water or the low water of rivers. 



Let us now quote from Cipolletti's 

 review of the conclusions of this con- 

 gress. He says :* 



The other part of the question, concerning 

 the influence of forests upon surface waters, 

 is perhaps the most important of all and to 

 all ; and it is, np doubt, the one upon which 

 our authors' opinions differ most. One may 

 state, that they all recognize, or at least none 

 denies, the beneficial influence of forests upon 

 the regimen of a river in its state of low- 

 water flow, high-water flow, and ordinary 

 floods; but many of the writers, we may say 

 the majority of them, deny that forests have 

 any power not only of preventing, but even 

 of mitigating to any appreciable extent the 

 more serious and damaging floods, which 

 occur in every country at certain periods. 



*This translation is not mine. 



The low-water flow as is commonly 

 known depends almost exclusively on 

 springs ; and having once admitted the fact, 

 that a covering of trees exerts a beneficial 

 influence upon the flow of springs, we may at 

 once draw from it the legitimate conclusion, 

 that the regimen of low-water flow of a river 

 is favourably affected by the existence of 

 forests in its basin; except, be it well under- 

 stood, the cases already alluded to, of an ex- 

 tremely permeable soil or of lands which can 

 be cultivated without the loss of the humus 

 covering, cases in which, as has already been 

 stated, it is possible that deforestation may 

 help the absorption of the water into subsoil 

 and thereby increase the volume of the low- 

 water flow in the general recipients, the 

 rivers. 



But with regard to the regimen of high- 

 water flow and ordinary floods, there is no 

 material difference, of opinion. In such locali- 

 ties the waters running off the surface unite 

 with the springs in providing the supply of 

 water for a river. Thus, all the writers agree 

 that forests exert a moderating influence on 

 the run-off of surface waters, owing to a large 

 proportion of the water being retained by the 

 leaves and other parts of the plants, also on 

 account of the quantity of it being absorbed 

 by the layers of dead leaves, moss and humus 

 which form the top covering of the forest 

 ground, and partly also to the obstruction 

 which roots above ground form to the rapid 

 flow-off of the surface water, by forcing it tc 

 remain stagnant in a thin sheet, instead of 

 accumulating in a mass and running off 

 quickly in the shape of brooks, which is 

 what happens where the surface water finds 

 little obstruction and is apt to produce ero- 

 sion. To this may be added, in the case of 

 cold climates, the additional advantage that 

 the snow lies longer in the forest and melts 

 here more slowly than in the open country. 

 To conclude, forests act as real regulators, 

 obliging the rain water to flow much more 

 slowly to the bottom of the valley, than it 

 would do otherwise, and by this means en- 

 suring a more uniform and continuous flow 

 in the lower reaches of rivers. 



But, as already stated, opinions differ 

 widely the moment we approach the subject 

 of phenomena which are apt to produce 

 heavy and extraordinary floods. Some of the 

 authors (Messrs. Ponti, Keller, and Wolf- 

 schutz) assert with insistence that heavy 

 floods are due entirely to climacteric causes 

 and that, consequently, the influence of forests 

 is nil, or at any rate so small, that it can 

 be neglected altogether. The reasoning by 

 which they arrive at this conclusion is as 

 follows : These great and extraordinary 

 floods, they assert, only occur after down- 

 pours lasting several days ; hence, under sim- 

 ilar circumstances, we must take it for 

 granted that the leaves and all other parts 

 of the plants have already soaked up the 

 maximum quantity of water they are able 

 to retain, that the upper layer of the soil 



