DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 471 
of decomposing vegetable matter which forms the forest floor * * * Mr. Chitten- 
[citation of foreign authorities] * * The function of the forest 4° 
and of the humus beneath as a storage reservoir is of high importance.” 
To the same end is the following, from the report of the Secretary 
of Agriculture, on the Southern Appalachian and White Mountain 
Watersheds, submitted to Congress December 11th, 1907 (pp. 16-17): 
“There is but one natural factor which tends to equalize the flow 
of the Southern Appalachian streams—the forest. In one continuous 
mantle, covering ridges, slopes, and coves, it has for untold ages been 
nature’s sole reliance for the proper distribution of rainfall. If storm 
and deluge came, the downpour fell upon a foot-deep layer of humus, 
which readily received many times its own weight of water before it 
allowed any to escape. When filled, it passed on the excess to a soil 
made porous by myriads of penetrating roots and countless tons of 
vegetable mold. If drought came, it found the humus and soil filled 
as a reservoir with water for the steady supply of springs and streams 
through weeks or months of rainless weather. * * * It was as 
efficient as would have been a system of lakes. It had power to hold 
back the water on a steep mountain side almost as though the ground 
were level.” 
Read this twice, for it is not only an authoritative announcement 
that the humus is a reservoir, but it shows that the free play of the 
imagination has its place even in the most serious public document. 
Of course there can be no dispute over the fact that the forest bed, 
wherever it exists, has a storage capacity, and why Mr. Leighton now 
says it has not, is a mystery. If he had said that such capacity is 
greatly over-rated in the popular estimation, he would have been 
entirely correct, but that it does exist to some extent is not to be 
questioned, and in certain situations it is quite large. The point of 
essential importance is that it gives up that storage along lines of 
least resistance, whether those be by percolation into the ground, by 
run-off from its surface, or by evaporation into the air. In proportion 
as the soil itself is porous and the surface slope small, the quantity 
absorbed into the soil will be greater. And, conversely, as the soil is 
compact and impervious and the slope steep, the quantity that runs off 
will be increased. In times of prolonged drought, it may absorb the 
whole of such fugitive showers as come along, and give them up in 
evaporation. But it must be carefully borne in mind that in any 
storm capable of producing a flood, this storage capacity becomes com- 
pletely exhausted before the storm has progressed far, and thereafter 
it has no appreciable power to modify the flood. It would probably 
be a liberal estimate to say that, in our eastern deciduous forests, $ in. 
of rain in a continuous shower would exhaust the storage capacity of 
a fairly dried-out forest bed; 3 in. in the Rocky Mountain forests, and 
from 1 to 2 in. in those of the Pacific Coast.* 
*This subject should not be confounded with that of the storage capacity of the 
round itself below the immediate surface. This is exceedingly variable, depending upon 
its geologic structure. 
