FOREST COVEE IN PROTECTING RESERVOIRS 9 
RELATIVE VALUE OF FOREST AND OTHER COVER IN REDUCING 
EROSION OF SOIL 
It is sometimes claimed that any other ground cover or even 
masonry dams will adequately replace the forest as a protective 
agency. (PL 7). In the case of brush the protective efficiency may 
be as great as that of the forest ; but brush provides no merchantable 
products such as woodland produces and is therefore uneconomical. 
In the case of grass, it is more than doubtful if its protective ef- 
ficiency is as great as forest in the Rocky Mountains, south of Idaho, 
and in the southern Appalachian and southern Piedmont regions 
which are the regions where protection is most urgently needed. 
In these regions there are many types of soil and many sites — warm 
and dry southern slopes — on which a permanent sod can not be main- 
tained. To be handled as a profitable investment on such sites, 
grass must be reset at frequent intervals. At such periods the naked 
soil is exposed for several months. In contrast, the continuity as 
well as the completeness of the protection afforded by woods, if 
fire is kept out, is of the highest value. 
Another advantage of the forest is the greater permeability of the 
soil — the deep-root zone, 3 to 4 feet, penetrated by the many chan- 
nels resulting from the decay of roots and rootlets as far down as 
the roots extend. The influence of the roots of trees is evident wher- 
ever a new road is cut through a forest ; for along the sides of such 
new excavations during wet weather streams of water can be found 
trickling and even spouting from root holes as far down as 3 or 4 
feet below the surface. 
The statement has been made by Mead 13 that the forest cover exer- 
cises no influence on permeability. This may be largely true of 
sandy and glaciated soils, such as he had under observation in north- 
ern Wisconsin, and it probably holds true for such soils independent 
of location. One of the steadiest small streams in the Eastern 
States is Hitchcock Creek, Richmond County, N. C, a sand-hill 
stream with little vegetative cover on the stream basin but with a 
highly absorptive soil. A test which was conducted a few years ago 
by the author shows the comparative permeability and depth of the 
root zones of the forest and grassland, and yields results of most 
positive significance. Adjoining areas of forest, old grassland, and 
old farm land, with the same slope and aspect, were selected, and 
during the winter, when transpiration of moisture by the forest was 
largely eliminated as a factor, measurements were made of the mois- 
ture content of the surface soil and of the subsoil at 3 feet. The 
forest soil during the winter was invariably the most dry, showing 
the greater permeability. The subsoil of the grassland, deficient in 
root drainage, was usually wetter than the forest soil, also the sur- 
face soil of the grassland was often wetter. Both surface soil and 
subsoil of the naked land were always wetter than those of the 
near-by forest, except where the naked surface soil had been dried 
out by high wind. Newly cleared land, however, exhibited nearly 
the same conditions as that bearing forest trees. 
Of all surface covers which can be employed in reducing soil 
erosion the forest is the most efficient and most permanent. The mat 
13 See footnote 8. 
99224°— 26 3 
