FOREST LANDS FOR THE PROTECTION OF WATERSHEDS. 67 



cipitation and giving it more time to soak into the ground; but in fact this 

 benefit does not result. The water from the first melting of the snow blanket 

 does not sink into the ground but into itself. Snow is like a sponge. A panful 

 will shrink to one-fourth of its volume, or less, before any free water appears. 

 The author has seen an 8-foot covering of snow dwindle to 2 feet, with the 

 ground beneath is still comparatively dry. 



The forest shade thus holds the snow, which gradually becomes saturated 

 from its own melting, until the heat and warm rains of late spring or early 

 summer arrive, the soft air everywhere pervading the forest depths and finding 

 a maximum exposure of surface to the melting influences. A cubic yard of 

 snow, which in a great drift might stand 27 feet deep with a square foot of 

 exposure, may here lie with a depth of 1 foot and 27 square feet of exposure. 

 The result is that when the final melting begins the whole body of snow dis- 

 appears very rapidly, rushing from every direction into the streams, swelling 

 them to their limits and often causing disastrous freshets. The active melting 

 lasts but a short time, and there is little opportunity for the water to soak into 

 the ground. The delay in melting, caused by the forest shade, has simply 

 operated to concentrate it into a shorter period and increase the intensity of the 

 resulting freshet. It comes so fast that the greater portion of it can not be 

 utilized at the time and is lost altogether unless intercepted by reservoirs. 



In the open country, on the other hand, the drifts last for weeks after the 

 snow has entirely disappeared from the forest, and continue to yield a supply 

 of water far into the summer. The period of active melting in the open may 

 have lasted four mouths, that in the forest scarcely as many weeks. In the 

 northwest corner of Wyoming and contiguous portions of the adjoining States 

 lies an elevated region of probably 20,000 square miles, which is the source of 

 nearly all the great river systems of the West. It is a very remarkable region 

 in this respect. Its average altitude is about 7,500 feet, and it is in large part 

 covered with a dense evergreen forest. At the very summit of this elevated 

 region is that singular section now visited annually by thousands of tourists 

 the Yellowstone Park. The opening of the tourist season in spring occurs just 

 about the time of active snow melting, and the most onerous and difficult task 

 of those in charge of the road system of the park is to get the roads into con- 

 dition for the first travel. This frequently has to be done while the snow still 

 lies deep on the ground. It was the repeated execution of this task that first 

 drew the author's attention to the fact that, as a general rule, the floods of this 

 region are forest floods, and that the same conditions of precipitation which 

 force the forest streams out of their banks produce only moderate effects in 

 the open. The traditional "June rise " comes mainly from the mountain forests. 



A photograph, taken about the middle of June in a year of heavy snowfall 

 and only two days before the tourist season opened, shows an east and west 

 road through a dense forest of lodgepole pine at an altitude of 8,200 feet. It 

 shows very effectively the deep, even blanket of snow everywhere covering the 

 ground, except along a narrow strip at the roots of the trees on the north side 

 of the road, where the sun had access through the opening in the tree tops 

 caused by the 30-foot clearing for the roadway. Another, taken practically at 

 the same time, shows one of the great drifts in the open country, which it was 

 impossible to avoid in locating the road. 



At this time a period of very warm weather had set in, with frequent rains. 

 Severe floods followed, which did great injury to the roads and bridges, not 

 only in the mountains, but for a considerable distance below. Within two 

 weeks the snow had practically disappeared in the forests, but in the open 

 country the drifts, like that in the photograph, continued until the middle of 

 July, giving forth a continuous supply of water. 



A most illuminating article, and one which everyone interested in the subject 

 should read, was published in Science for April 10, 1896. It gives the results 

 of observations in the mountains of Nevada for over twenty-five years, during 

 which " extensive tracts of timber " were cut off " to the very ground " and new 

 growths had been well started. It was found that springs which were active 

 after the land was cleared dried up when the new forest growth developed; 

 " that the water supply from the mountains is greater and more permanent 

 now than it was before the timber was cut off; " that freshets were no more 

 " frequent or violent than before the trees were cut off," and that " spring 

 floods were less frequent." The greatly increased loss due to evaporation in 

 the forest was pointed out. This results partly from the vast extent of surface 

 on the ground exposed to the air and partly from exposure on the leaves and 

 branches of the trees. 



