l62 



AMERICAN FORESTRY 



Investigations undertaken by Bavar- 

 ian foresters upon the volume of water 

 that dead leaves and other organic 

 debris of the forest floor can absorb 

 have been recorded by Ebermayer. 

 These investigations have shown that 

 one cubic meter of dry beech leaves 

 absorbs two to two and a half times 

 its weight of water, one cubic meter of 

 dry needles of spruce and Sylvester pine 

 one and a half to two times its weight 

 of water, and one cubic meter of moss 

 two and a half to three times its weight 

 of water. 



The Bavarian foresters might be crit- 

 icized for having experimented on 

 leaves that were more or less stirred 

 up, not lying as they do on the ground, 

 the experiments having been made upon 

 a certain volume of leaves dried in the 

 air, heaped in a vessel, then placed in 

 a sack, which was jjlunged into water 

 and weighed after two days' saturation. 



Ihe lamented Julien Calas, chief 

 guard of the forests at Prades, made 

 experinients on the forest floor ex- 

 actly as it lies on the ground. It was 

 weighefl the first time after complete 

 saturation and the second time after be- 

 coming entirely dry through evapora- 

 tion in the open air. .\ccording to Mr. 

 Calas, oak leaves absorb nine times their 

 weight of water, those of the beech and 

 pine eight and five tinges their weight 

 of water. 



Finally ^Ir. Henry, professor in the 

 national school of waters and forests, 

 likewise experimented with tlu' forest 

 floor just as it lies on the soil. After 

 a section of it had been plunged into 

 water for several days, until it was com 

 pletely saturated, he let it drain, weighed 

 it saturated with water, then dried it at 

 TOO degrees and weighed it again. He 

 found that a carpet of spruce needles, 

 taken as they lie and composed of leaves 

 in all degrees of decomposition, absorbs 

 on an average more than four times its 

 weight of water. 



Beech leaves, after twelve days of 

 saturation, absorb 4.41 times their 

 weight of water.' Mr. Henry con- 

 cludes from his experiments that the 

 spruce needles which cover the forest 

 soil over one hectare can retain 105,825 

 kilograms of water; that is, a rainfall- 

 of ten and one-half millimeters for an 

 average depth of .02 of a meter. As 

 clumps of spruce retain in their tops 

 and allow to evaporate there about 

 half the rainfall, it would require a fall 

 of 21 millimeters for the soil under the 

 needles to begin to become moist. 



It is evident that the retentional ca- 

 pacity of the soil cover is not infinite 

 and that it fails following rains that 

 are exceptionally heavy, such as those 

 cited by Mr. Wolfschiitz ; but such rain- 

 falls are fortunately rare, and neither 

 the facts noted by Mr. Wolfschiitz nor 

 the hydrological observations of Mr. 

 Lauda lessen the value of the experi- 

 ments that we have just reviewed; 

 finally, as the latter said, the data that 

 we have gathered up to the present 

 time is not sufficient basis for a final 

 judgment. 



We may wonder, it is true, that 

 densely wooded river basins have been 

 visited by disastrous floods. But is not 

 the cause of this j^henomena the more 

 abundant rainfall there? We know ab- 

 solutely that the presence of forests 

 increases to a marked degree atmos- 

 pheric precipitation. In mountainous 

 countries, especially, forests cause fre- 

 quent atmospheric depression because 

 they block the passage of air currents 

 and force them upward toward the 

 higher strata of air, which are colder. 

 The air within and above the forest is, 

 moreover, colder and more humid than 

 the surrounding air. The result is fre- 

 quent condensation of the clouds into 

 rains in the neighborhood of mountain 

 forests. Conseciuently, it is not to be 

 wondered at that the streams of the 

 forested regions cited by Mr. Wolf- 



'E. Henry, Faculte d'imbibition de la couverture morte, Rcvuc dcs Eaux ef Forets, 

 June 15, 1904, pp. 353 to 361. .-Xccording to M. Henry, the differences that appear between 

 the results of his experiments and those obtained by tiie German foresters come from the 

 differences in the degree of decomposition of the leaves. The further advanced the decompo- 

 sition of the organic del)ris that constitutes the forest Hoor. the greater is the capacity 

 of imbibition. 



