CHAPTER I 
THE INFLUENCE OF FORESTS ON CLIMATE 
THE influence of forests on climate is undoubted, though 
perhaps less than is generally supposed. The subject is a 
difficult one to study; and on many points no agreement 
has been arrived at amongst engineers and foresters. The 
latter usually hold that the presence of forests is beneficial, 
in increasing the amount of rain in a district or country, 
and in diminishing the erosion (Frontispiece) and the con- 
sequent great losses of the soil on hill and mountain slopes. 
The foresters agree with Humboldt’s saying: “ How foolish 
is man in destroying the mountain forests, as thereby he 
deprives himself of wood and water at the same time.” 
The desolation that now prevails in parts of Spain, 
Algeria, and other Mediterranean lands is generally ascribed 
to the gradual drying up of the climate, consequent on the 
lessened rainfall brought about through the steady clearing 
of the forests by human agency. It is, however, well 
established that great climatic changes of cosmic origin 
occur in the course of centuries; and the disappearance of 
the forests in those countries may be possibly not the cause 
but the result of lessened rainfall in the present epoch as 
compared with Roman times. 
Numerous observations taken over short periods of years 
in France, Germany, and the United States show that 
forests exert in the districts which they cover a definite 
influence on the temperature of the air and of the soil, on 
the rainfall, on the melting of the snow, on the water supply 
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