TRANSPIRATION — SNOW. 137 



ELEMENTS OF CONSERVATION. 



In discussing tbe elements of dissipation as to tlie degree of their 

 effect under forest-cover, compared with the same elements at work 

 in the open field, we have seen that the shade, the low temperature, 

 the relative humidity, the absence of violent air-currents, the water 

 capacity of the forest floor, are all acting as factors of conservation. 

 We have seen that the quantity of water lost by evaporation— the 

 most fruitful source of dissipation— may be more than six times as 

 great in the open as in the forest. There is ouly one other element of 

 conservation affecting water supplies which requires special mention. 

 This is the retardation in the melting of the snow, which is due to 

 forest-cover. According to Dr. Biihler, of Zurich, this retardation in 

 Switzerland amounts to from five to eight days in general, and may, 

 according to weather conditions, be several weeks, thus giving a longer 

 period for distribution. The evergreen coniferous forest in this respect 

 naturally does better service than the deciduous one. 



Effect of forests in case of snoiv. 



Snow will lie in the forest more evenly and continuously than on the 

 open, wind-swept areas. Thereby not only the amount finally remain- 

 ing for drainage is increased, but the soil is prevented from freezing, 

 and is kept open for percolation when the snows melt. The retarda- 

 tion of the melting has been determind by Biihler in Switzerland to be 

 from eight to fourteen days. 



Mr. R. U. Piper, in his Trees of America, states that an unobstructed 

 warm wind will dissolve the snow more than ten times as fast as when 

 it is protected from the wind, the temperature being the same, and he 

 adduces in verification of his statement the following experiments tried 

 by himself: In the first, a body of snow 1 foot in depth, protected from 

 the wind, but partially exposed to the sun, after a thaw of two weeks, 

 was not wholly melted, while another mass 6 feet in depth, more shel- 

 tered from the sun, but fully exposed to the wind, was melted in less 

 than a week. 



In the second, equal quantities of snow were placed in vessels of the 

 same kind and size and exposed to the same temperature, one being 

 covered and the other having a current of air constantly passing over 

 it. The snow in the latter vessel was melted in sixteen minutes; that 

 in the former was not entirely dissolved at the end of eighty-five min- 

 utes. 



In the third experiment, in a room with the temperature above 

 80O, the mercury in a thermometer rose from 32° to 80° when exposed 

 to a warm current created by a fan, or seven times as last as when the 

 heated air was still. 



The conservative effect of the forest-cover is especially of value on 

 the western mountain ranges, which are liable to be swept by the 



