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diminish evaporation from the soil; make the days cooler and the nights warmer. [Because changes of temperature take place slowly in trees, but rapidly in air, and also because trees obstruct nocturnal radiation, and, when the locality is a slope with trees at the top, they obstruct the descent of currents of cold air.]
Soils.
The surfaces of loam and clay soils do not heat as do the surfaces of sandy soils, because the former soils being the better conductors, the heat does not accumulate on the surface, but is propagated downwards; and for the like reason the surfaces of rocks are cooler than either.
Arid regions are commonly deficient in vegetation, and by consequence are deficient in rain-fall.
The Sea.
The sea and deep lakes moderate nocturnal winter temperatures. [Owing to the high specific heat of water, its temperature falls more slowly than that of land; and when radiation cools the surface layers, they sink to the bottom, and are replaced by other layers which are of higher temperatures. A constant change is therefore going on, and the result is that the superjacent air is very little chilled on calm nights.]
Mountains.
Mountains deprive of their moisture winds which cross them, and thus cause cold winters
