1 68 North American Forests and Forestry 



The humus accumulating on the floor of forests, 

 the litter of dry leaves, the cushions of moss and 

 covering of herbage have a tendency to soak up 

 the rain-water and hold it much longer than it 

 would be held by the comparatively thin vegetable 

 covering of grass-covered areas, let alone slopes 

 devoid of dense vegetation. The shade of the 

 forest also retards evaporation of the water after it 

 has fallen, and the tangle of dead trees, branches, 

 and leaves often obstructs the flow of streams and 

 causes the water to form pools and swamps that 

 are drained but slowly. The tendency of forest 

 covering is, therefore, to make the processes of 

 evaporation, percolation of the ground, and run- 

 ning off of surface water proceed much slower than 

 in the open country. Consequently, the rivers fed 

 from forest regions are apt to have a more regular 

 flow. The floods after heavy rains, or after the 

 melting of the snow, will not be quite so high, and 

 the low-water stage will not come quite so quickly 

 after the rain has ceased. So much is certainly 

 true. But it is not correct to assume that the 

 great floods occasionally doing so much damage 

 along the Mississippi and other great river systems 

 have been caused by the destruction of forests 

 around the headwaters. In the first place, the 

 deforestation around these headwaters has not been 

 excessive. In the second place, great floods were 

 known long before settlement in these regions had 

 made the slightest inroads upon forests, as can be 

 learned from the notes scattered through the 



