158 



AMERICAN FORESTRY 



us in the beg-inning that "the study of 

 water supply is one of the most difficult 

 problems of hydrography." To solve 

 the problem, Mr. Lauda made minute 

 and very accurate observations in 1903 

 and 1904, on the amount of rainfall and 

 run-off in the basins of two rivers of 

 Moravia, the Bistritzka and the Seniza. 

 The distance between these two basins 

 is about twenty kilometers. They are 

 similar in the character of the soil, in 

 topography, and in the relative propor- 

 tion of different kinds of vegetation. 

 Their areas are, respectively, 6,380 and 

 7,400 square kilometers, but forests 

 cover forty-eight per cent of the terri- 

 tory in the basin of the Bistritzka, while 

 they cover only twenty-seven per cent 

 in that of the Seniza. 



The conclusions drawn from these 

 observations are not at all unfavorable 

 to the forest. They are as follows : 



The retention of rainfall is in a certain 

 measure greater in the more heavily zvooded 

 basin than in the less heavily zvooded one. 



For abnormally heavy precipitation — as for 

 example, at the time of flood — the retention 

 is less in the more heavily wooded basin than 

 in the one less rich in forested area that 

 is to say that in the latter case, after reach- 

 ing a certain degree of saturation, the surplus 

 of water that was formerly retained by the 

 forest flows off more perceptibly. 



After a dry period the effect of rainfall 

 is manifested more rapidly and more pro 

 gressively in the less forested areas, while 

 the inverse is true in the basin with the 

 greater forest area. 



Mr. Lauda does not deny, then, the 

 retentional capacity of the forest ; on 

 the contrary, he distinctly recognizes it, 

 except in the case of extremely abinid- 

 ant rainfall, when the roles seem re- 

 versed and the forest soil, saturated 

 with water, no longer retains the rain 

 that falls, but even allows the escape in 

 part of water that it had retained be- 

 fore. 



Mr. Lauda stated that on the loth 

 of September, 1904, after a dry period 

 of more than three months, a very 

 heavy rainfall occurred of about the 

 same depth in the two basins, but the 

 rise of the waters did not become ap- 

 parent in the basin of the Bistritzka, 

 which is more heavily wooded, until 

 two days after the flood occurred in the 



basin of the Seniza, which is less heav- 

 ily forested. Similar observations were 

 made in 1904. 



The retentional capacity of the forest 

 after a dry period is then well estab- 

 lished, and if it is not effective under 

 all circumstances, it proves that the in- 

 fluence of the forest has a limit, which 

 is not to be wondered at. 



We might examine the figures given 

 by Mr. Lauda ; but even with the prob- 

 ability that the volume of water con- 

 stituting the run-off from each river 

 could have been calculated exactly, al- 

 though errors might easily be made in 

 the case of high floods, it is difficult 

 to admit that the amount of rainfall 

 could have been gauged with sufficient 

 accuracy. A number of rain gauges 

 scattered over an area of 6,000 to 7,400 

 square kilometers is not sufficient to es- 

 tablish mathematically the exact depth 

 of rainfall. Moreover, is Mr. Lauda 

 right in saying: "Final judgment can- 

 not be passed yet, however, upon the in- 

 fluence of forests on stream-flow, as the 

 data that has been gathered up to the 

 present covers only a relatively short 

 period of time?" We must wait, then, 

 before declaring the theories accepted 

 up to now in regard to the influence of 

 forests on floods, barred by limitation 

 and before treating the action of the 

 forest as merely claimed, not estab- 

 lished. 



If Messrs. Wolfschiitz and Lauda 

 have appeared to some to oppose in 

 their papers the ideas accepted up to 

 now in regard to the action of forests 

 in lessening floods and feeding springs, 

 it is by no means the same with ^lessrs. 

 Ponti and Lokhtine, wdiose papers are 

 veritable pleas in favor of the forest. 

 In reading them, one is convinced that 

 at the congress at Milan the "partisans 

 of the forest" have indeed furnished 

 some facts and interesting observations 

 to support their claims. 



Mr. Ponti gave in his paper a strik- 

 ing picture of the condition to which 

 Sardinia was reduced after the clear- 

 ings made on the island in 1870, which 

 lowered the percentage of forested area 

 from forty-three per cent to twenty-six 



