40 ELEMENTARY FORESTRY. 



than six times as great in the open as in the forest. The only 

 other conservative effect of forests on water supplies is their 

 effect in retarding the melting of the snows. This acts as an 

 important function in the prevention ot freshets by giving the 

 snow a longer time to melt, so that the snow water has a bet- 

 ter chance to sink into the ground. It is of course more evi- 

 dent in evergreen than in deciduous forests. On the grounds 

 of the Minnesota Experiment Station, where the woodland con- 

 sists of a low growth of Oak, the snow is often retained in the 

 woods a week longer than in the open. This often allows the 

 snow water from the fields to almost wholly run off before it 

 has begun to flow from the woods. Then again the daily flow 

 of snow water from the woods is much shorter than from the 

 open fields during spring weather, when we have warm days 

 and cold nights, for it begins later in the morning and stops 

 earlier in the afternoon. Under the dense shade and mulch of 

 the cedar swamps of northern Minnesota the snow and ice 

 often remain until the beginning of summer. The Indians claim 

 there has never been a time when they could not find ice for 

 their sick in the cedar swamps of that section. This retarding 

 effect on the melting of snows in the spring and in preventing 

 the run-off is of far greater importance in the case of streams 

 that rise in the high mountains than in Minnesota and Wiscon- 

 sin, where the land is more nearly level. Where streams have 

 their sources in mountains, as those of Colorado and other 

 Rocky Mountain States, the cutting away of the forests causes 

 a heavy flow of water early in the spring and little water in the 

 summer, when it is most needed for irrigation purposes. This 

 has become so evident that the Chamber of Commerce of Den- 

 ver, Colorado, recently petitioned the President of the United 

 States to reserve such land, in forests and administer it at public 

 expense, and in their petition used in part the following lan- 

 guage: 



"The streams upon which the irrigation system of Colorado 

 depends are fed by the springs, rivulets and melting snows of 

 the mountains, which in turn are nourished and protected by 

 the native forests. Where the forests have been destroyed and 

 the mountain slopes laid bare most unfavorable conditions pre- 

 vail. The springs and the rivulets have disappeared, the winter 

 snow melts prematurely, and the flow of the streams, formerly 



