196 ACTION OF THE FOREST ON THE SOIL. 
The effect of the forest on precipitation, then, is not entirely 
free from doubt, and we cannot positively affirm that the total 
annual quantity of rain is diminished or increased by the de¬ 
struction of the woods, though both theoretical considerations 
and the balance of testimony strongly favor the opinion that 
more rain falls in wooded than in open countries. One im¬ 
portant conclusion, at least, upon the meteorological influence 
of forests is certain and undisputed : the proposition, namely, 
that, within their own limits, and near their own borders, 
they maintain a more uniform degree of humidity in the 
atmosphere than is observed in cleared grounds. Scarcely 
less can it be questioned that they promote the frequency of 
showers, and, if they do not augment the amount of precip¬ 
itation, they equalize its distribution through the different 
seasons. 
Influence of the Forest on the Humidity of the Soil. 
I have hitherto confined myself to the influence of the 
forest on meteorological conditions, a subject, as has been seen, 
full of difficulty and uncertainty. Its comparative effects on 
the temperature, the humidity, the texture, and consistence, 
the configuration and distribution of the mould or arable soil, 
and, very often, of the mineral strata below, and on the per¬ 
manence and regularity of springs and greater superficial 
watercourses, are much less disputable, and more easily esti¬ 
mated, and much more important, than its possible value as a 
cause of strictly climatic equilibrium or disturbance. 
The action of the forest on the earth is chiefly mechanical, 
but the organic process of abstraction of water by its roots 
affects the quantity of that fluid contained in the vegetable 
mould, and in the mineral strata near the surface, and, conse¬ 
quently, the consistency of the soil. In treating of the effects 
of trees on the moisture of the atmosphere, I have said that the 
forest, by interposing a canopy between the sky and the 
ground, and by covering the surface with a thick mantle of 
fallen leaves, at once obstructed insolation and prevented the 
