December 6, 1912] 



SCIENCE 



799 



This problem is of vital importance to irriga- 

 tionists and power companies wherever 

 streams are fed by snow. 



The data for the study of this problem are 

 very abundant. Mount Rose is situated be- 

 tween the heavily forested main chain of the 

 Sierra Nevada and the scantily forested 

 ranges of the semi-arid Great Basin, and 

 forms the natural headquarters for the study 

 of both. On the flanks of Mount Eose and its 

 subjacent range are also wide areas long since 

 deforested and now in various stages of re- 

 forestation, while the apex of the mountain 

 furnishes abundant opportunity for studying 

 the snow where it falls deepest and longest. 

 The observatory building on the summit has 

 now been supplemented by a headquarters 

 camp, made of sandbags, at Contact Pass 

 (elev. 2,744 meters) and another camp at the 

 base of the mountain. By means of this 

 chain of stations, measurements of snow 

 depth and density, the evaporation of snow, 

 and temperatures within the snow have been 

 conducted on the mountain for limited 

 periods. 



Adjacent to Mount Rose is the basin of 

 Lake Tahoe, where a coast line seventy miles 

 long has furnished ready access throughout 

 the winter, by means of motor boat and ex- 

 plorer's camp, to forests of various types and 

 densities, and to all the typical slopes and ele- 

 vations found in the Sierra Nevada. 



The study of the conservation of snow was 

 begun with camera in the winter of 1906, and 

 in the spring of 1909 there was designed a 

 snow sampler by means of which cores can be 

 obtained from snow-fields of all depths and 

 densities, the water content of the sample 

 being determined by weight. Soon after, a 

 spring balance was devised that would indi- 

 cate without any computation the equivalent 

 water in the sample irrespective of variation 

 in the length or weight of sampler used. By 

 means of these instruments thousands of 

 measurements have been made, and the quan- 

 titative value of forested areas and their su- 

 periority over unf crested was early established. 



The minute investigation of the various 

 phases of the problem has proceeded more 



slowly, but considerable progress has now been 

 made toward their solution. The general 

 principle underlying the conservation of 

 snow is that of protection against evapora- 

 tion and melting by wind and sun. Snow 

 lies longest where it falls deepest. Cliffs and 

 lee slopes are large gatherers of snow. Yet 

 wherever forests crown such slopes the ca- 

 pacity of these slopes to gather and conserve 

 snow is increased. In wind-swept regions, 

 timber screens have a snow-gathering capacity 

 varying according to their height and imper- 

 viousness to the wind. They also, by check- 

 ing the wind, reduce the evaporation of snow, 

 which under the influence of a wind move- 

 ment of 33 miles per hour, despite the fact 

 that the snow was frozen, has reached in a 

 single night the total of .10 in. moisture eon- 

 tent, or one one-hundred-twentieth of the total 

 snow on the ground. 



The action of unbroken forests upon the 

 snow is unlike that of timber screens, particu- 

 larly on the lower slopes where the wind is less 

 violent. These forests catch the falling snow 

 directly in proportion to their openness, but 

 conserve it, after it has fallen, directly in pro- 

 portion to their density. This phenomenon is 

 due to the crowns of the trees, which catch the 

 falling snow and expose it to rapid evaporation 

 in the open air, but likewise shut out the sun 

 and wind from the snow that has succeeded in 

 passing through the forest crowns to the 

 ground. 



The most efficient forest, therefore, from 

 the point of view of conservation is the one 

 that conserves the largest amount of snow to 

 the latest possible time in the spring. This 

 has been found by measurement to be the for- 

 est with a maximum number of glades, which 

 serve as storage pits into which the snow can 

 readily fall but the wind and the sun can 

 not easily follow. One such forest was found 

 to have conserved at the close of the season of 

 melting three and one half times as much 

 snow as a very dense forest adjacent to it. 



The most efiicient type of forest found at 

 levels below 8,000 feet is the fir, whose foliage 

 is much more impervious to the rays of the 

 sun than that of the cedar or pine. At 8,000 



