138 FOREST INFLUENCES. 



cbinook, dissipating as if by magic the snew-cover over wliicli it 

 sweeps. (See p. 133.) 



Even without this specially dry wind it is well known in Colorado 

 and other luountain districts that the regular wind sweeping over the 

 bare slopes above timber line, or where the forest-cover is removed, 

 while they drift the snow hither and thither, they " wear it out" at the 

 same time. By the blowing of the wind the snow is reduced to finest 

 particles, and, by the shifting, new surfaces are constantly exposed — 

 two processes which greatly fticilitate evaporation, and thus the snow 

 is literally worn out. 



The proposition, then, to remove the forest-cover in order to allow 

 the drifting and compacting of the snow, from which possibly to secure 

 a longer period of distribution, even if there were no other objection, 

 must be considered a hazardous and ill advised expedient. 



The influence of the forest upon the condition and driftingof the snow 

 is g-raphically related by Middendortf in his description of Siberia, 

 speaking of the Bnran or snowstorm characteristic of the treeless 

 plains of tundras: 



As far as tlie forest readies ami impedes tie action of the winds the snow lies 

 everywhere evenly and loosely, so that in the beginning of winter one can travel 

 only on snowshoes. As soon as the tundra is reached there is no need of snowshoes. 

 The snow lies either like a thin carpet, or drifted together in incredible masses, so 

 compacted as to bear man and beast, etc. 



General effect of forests in reducing evaporation. 



The popuhir notion which ascribes to the moss-cover or spongy char- 

 acter of the forest floor a conservative function beyond that of retard- 

 ing evaporation and expediting infiltration seems to be entirely errone- 

 ous and needs revision. The idea that the moisture of the soil and the 

 flow of springs is increased by water from the spongy cover is alto- 

 gether in contradiction to physical laws, and can be shown experimen- 

 tally to be a mistaken one. 



Water filters through the cover by the law of gravitation until the 

 whole mass has become fully saturated. With an addition of water it 

 will filter through to the soil, as long as the supply continues and as 

 long as the soil is not so saturated that it can not readily absorb any 

 more water. At last, the supply continuing, the cover will refuse to 

 convey it and will shed it superficially, leaving opportunity to reach 

 the soil only where the moss cover is interrupted. When the water 

 supply ceases, evaporation begins above, and by capillary attraction 

 the cover supplies its loss of water on the surface from the soil below. 



To give water to the strata below, it would be necessary that these 

 should have become dry, or at least drier than the moss-cover before the 

 latter had lost its water. This may occur and depends naturally upon 

 the structure and nature of the soil. If the soil is strongly fissured, 

 thus rapidly draining the upper strata, then, if the moss-cover is still 



