DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 391 
in a region of moderate rainfall and porous soils (Nevada), where mr. Willis. 
this effect was a maximum before the new growth used much water. 
If the young forest were vigorous enough and could be given time 
enough to grow to the stature and density of the old stand, it would 
eventually re-establish the conditions that existed under the virgin 
forest; but in any case? during the growth of the young forest, even 
under the best conditions, erosion has begun its insidious work. The 
gully that is cut in the forest cover may be but a few inches deep, 
or, as frequently the case in the Southern Appalachians, many feet 
deep; it may be covered by logs, brambles, and weeds; but it lowers 
the level of discharge by a corresponding amount and gains an ad- 
vantage for attack upon the entire slope. That advantage it never loses, 
and the effect is the removal of the superficial soil at first and ulti- 
mately of all the soil which is above the level of discharge of the 
mouth of the gully. Though this ultimate effect be deferred for 
a long term of years, it will certainly be reached. In the high 
mountains one has only to climb the crags above the tree-line to see 
the result. In the Southern Appalachians, where the soil is decom- 
posed rock, of impervious texture and great depth, one has only to 
consider the logging chute and the old field. There, from virgin forest 
to abandoned field is frequently an interval of but five years, and, 
while it is true that the farmer has a worse record than the lumber- 
man, the difference will not be material fifty years hence. In China, 
where the precipitation is much less and the conditions, consequently, 
less favorable to erosion, the writer has seen several thousand square 
miles of mountainous country like the Appalachians, which has been 
completely deforested, denuded to the bare rock, and depopulated, in 
the last century and a half. There is great reason to protest earnestly 
against any superficial observation which leads to the conclusion that 
no harm is done by reckless lumbering and ill-judged agriculture, 
because Nature with her wonderful recuperative power in some 
measure conceals the scars. 
“The commonly accepted opinion is that forests have a beneficial 
influence on stream flow: ae 
“(3) By increasing precipitation.” 
In opposition to views which are frequently supported by general 
rainfall statistics, and are endorsed by Colonel Chittenden, the writer 
holds that forests do affect precipitation; that they increase it slightly 
over that which falls upon green fields, and that they increase it notably 
over the amount received by bare plains under critical atmospheric 
conditions. He holds that these relations may be perceived over sufii- 
ciently wide level lands, but that they are particularly perceptible in 
the case of mountain ranges. More important, however, is the in- 
fluence of the forest or rock of a mountain range, because there the 
