468 DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 
Mr, tee forest can deny this.” The writer has personally supervised, or has 
otherwise observed, this scratching away on many hundreds of acres 
of ground in widely differing classes of forest, and he does deny it 
most emphatically. Once the rubbish is cleared away, a plow is just 
as necessary for loosening the soil as in the open country—more so 
than in land under active cultivation. So far as a rational comparison 
can be made, taking the country over, the writer would say that, in 
point of absorptive power, cultivated land ranks first, forest soil second, 
and old, well-trodden pasture or unbroken prairie soil third. 
Theorists expatiate upon the effects of tree roots in opening up 
the soil and rocks and keeping them porous,* often specifying both 
soil and rock in the same connection, as if the action of roots upon 
the two were not exactly opposite. A spike driven into the ground 
compacts it; into a rock, splits it. The roots of trees do not hang 
loose in the ground, like a sword in its scabbard. The bond is exceed- 
ingly close, and is so developed by the very necessity of keeping the 
tree from falling. 
One feature of the forest soil which restricts its absorptive power 
is the presence of the trees themselves, and this effect increases in 
proportion to the density of the timber. An acre of typical Washing- 
ton forest recently measured showed that 4.3% of the area at ground 
level was covered by the solid wood of trees of more than 10 in. in 
diameter. If the trees of smaller growth had been included, the cover- 
ing would doubtless have amounted to 5 per cent. But this represents 
only a minor part of the area actually excluded from absorption of 
rainfall. The large roots of trees spread very rapidly from the surface 
of the ground down. The earth around these roots and beneath the 
stump becomes densely packed through the weight of the tree and the 
stress produced by the wind, which develops a tight bond between roots 
and earth and ensures the stability of the tree. Those who have had 
experience in grubbing out stumps realize how close this bond is. It 
is a matter of common observation that the stumps of trees up-turned 
by the wind carry with them the solid mass of earth among the roots, 
and that this is so compact and hard that it often resists for years the 
action of the elements. This compacted soil is almost as impervious 
to water as the puddle wall of an earthen dam. Its area is from two 
to four times the stump area at ground level, and it is a fair assump- 
tion that in forests of average density 10% of the soil is thereby 
rendered not available for absorbing rain water. In very dense 
forests of large trees this percentage is undoubtedly greater. If these 
covered areas, of which one never thinks in looking at a forest, were 
spread out in the form of a concrete pavement they would make an 
impression. They evidently amount to as much as the ground covering 
*««The deep penetrating roots also open passages through which water ail: 
into the great reservoir of ground water.’ Pinchot, : sai aks 
