THE INFLUENCE OF FORESTS ON CLIMATE AND FLOODS 2ZZ 



is completely saturated and that the surface 

 waters have already reached the bottom of 

 the valley, when it is still raining in the 

 more elevated and more distant parts of the 

 catchment area. Under these circumstances, 

 they maintain, the volume of water which 

 comes down as rain is equal to the volume 

 of water which flows to the bottom of the 

 valley in the same time; in other words, the 

 moderating influence of forests — like that of 

 lakes and every other agency of this kind — 

 tends to fall off with increasing length of 

 time, while the phenomena lasts until finally 

 a point is reached when the efficiency be- 

 comes nil. Such is the fundamental argu- 

 ment of all these writers, and it does not 

 appear to us that anybody has given them 

 as yet a pertinent reply. Although I am 

 only a reporter, I may be allowed to inter- 

 pose in the question, because it does not ap ■ 

 pear to me that things happen exactly as 

 they might appear. In the first place, I mav 

 remark that in order to arrive at such a 

 necessary state of equilibrium, it is not 

 enough, that the phenomenon should last for 

 a sufficiently long period of time, but it is 

 also necessary that the intensity of the phe- 

 nomenon should also remain uniform dur 

 ing the whole period. Everybody will see, 

 how during the same period partial com- 

 pensation will take place, the outcome of 

 which will be a tendency toward the average 

 value of intensity, with an elimination of 

 the greatest crises, which in itself is already 

 a no mean advantage ; but there is still more 

 than this. By admitting that in consequence 

 of the prolongation of the rain, a moment is 

 at last reached when there is as much water 

 coming down into the valley as there is 

 coming down higher up in the catchment area 

 in the form of rain, it still has to be proved — 

 and, as a rule, this does not happen — that this 

 state of equilibrium coincides exactly with 

 the moment of the greatest intensity. In 

 every instance in which I had to study phe- 

 nomena of this kind in respect of lakes and 

 floodings of valleys, I found that this period 

 of equilibrium was reached invariably when 

 the rain was abating, that is, when a falling 

 off had already taken place in the intensity 

 of the phenomena ; in other words, that the 

 phenomenon had reached its maximum de- 

 gree of intensity before the moderating 

 power had become exhausted, the latter hav- 

 ing thus already made its beneficial influence 

 felt at the most critical period. 



If we next proceed to studying the ques- 

 tion by the light of recorded facts, doubts 

 arise and difficulties are met with, which 

 are perhaps not less serious. 



The advocates of the two opposite views 

 have endeavored, by means of minute and 

 most laborious researches, to get an insight 

 into the past and to see whether it was pos- 

 sible or not to discover any difference in 

 the regimen of great rivers for the past cen- 

 tury, a period from which, generally, dates 

 the deforestation carried out on a large 



scale in Europe; but they always found them- 

 selves face to face with very serious diffi- 

 culties, to which I will only allude briefly. 



All records which refer to great floods in 

 past centuries are always surrounded by so 

 rnany uncertainties and doubts, that it is most 

 difficult — not to say impossible — to draw any 

 certain and indisputable conclusions there- 

 from. We have a striking example of this 

 in the Tiber — a river after which the Nile 

 is certainly the most historical of all — in 

 the case of which it has been so far im- 

 possible to ascertain if its floods have under- 

 gone any change in the course of centuries. 



Can the destruction of forests bring about 

 a great deterioration and even the total loss 

 of the layer of cultivated soil of cultivated 

 lands, of those which are next to them, or 

 lying beneath them, and, even further off, of 

 the level portions of large valleys? Can it 

 also cause landslips, landslides, and aval- 

 anches ? 



Upon this point it will be very much more 

 easy for me to arrive at a conclusion be- 

 cause the authors of the papers, without dis- 

 tinction, and all technical experts generally 

 admit_ that tht deforestation of sloping lands, 

 especially if it is followed by a breaking up 

 and cultivation of the soil, ivill cause the 

 damages and injuries enumerated at the head 

 of this chapter. 



Otherwise, it is easy to understand, and 

 we are all daily witnesses of it, that when 

 land with a sufficiently steep slope is deprived 

 of the protection which roots of trees offer 

 against erosion, and still worse, when the 

 soil is subsequently broken up with plough 

 or spade, the water, being able to flow off 

 more quickly and to collect on a surface 

 which offers but little resistance, can very 

 easily remove and carry away with it to 

 the bottom the earthy materials which form 

 the cover, and leave the land denuded and 

 barren. One can also easily understand that 

 brooks, formed in this manner, can produce 

 similar effects as regards laying bare the 

 top of the slopes and carrying the material 

 to the bottom of the incline, a place where 

 the ground is better situated; and that the 

 deep gullies, which similar small but impetu- 

 ous, torrents scour upon the slopes of moun- 

 tains and hills, can in their turn also cause 

 the landslides and falls, especially if the un- 

 derlying rock is of a soft and friable nature, 

 and is, therefore, liable to being washed 

 away easily. It is equally evident that on a 

 slope, which is denuded of trees, avalanches 

 are more likely to occur and will be more 

 destructive than on a forest-clad hill, no 

 matter how steep the incline may be. The 

 influence of deforestation on valleys, even 

 when situated at a distance, though less ap- 

 parent and obvious, is nevertheless equally 

 certain and disastrous. 



Professor Moore quotes from Colonel 

 Chittenden's recent paper on the sub- 

 ject (pages 19 and 20). As I have 



