A. Because they retard evaporation, by keeping off the wind.
Q. If belts of trees promote warmth, why do forests produce cold?
A. 1st—Because they detain and condense the passing clouds:
2ndly—They prevent the access of both wind and sun:
3rdly—The soil of forests is always covered with long damp grass, rotting leaves, and thick brushwood: and
4thly—There are always many hollows in every forest full of stagnant water.
Q. Why do long grass and rotting leaves promote cold?
A. Because they are always damp; and the evaporation which they promote, is constantly absorbing heat from the earth beneath.
Q. Why do digging and ploughing help to make a country warm?
A. Digging and ploughing help to pulverize the soil, by admitting air into it, and this increases its mean temperature.