WHAT THE FORESTS DO FOR US 15 
the foot of the steep slopes badly cut by gullies two or 
three feet deep formed during a heavy thunder shower. 
Such lands, of course, should never have been cleared, 
because if the slopes are so steep and the soil so heavy 
that erosion is bound to oceur, the best use to which 
such land could be put is the raising of repeated crops 
of timber. 
The question of erosion in this country is one of 
great importance since no less than two hundred square 
miles of fertile farm lands are annually damaged by 
the action of erosion and flood. 
In checking the force of drying winds, forest belts or 
windbreaks also play an important role. In certain 
parts of the Middle West, windbreaks are almost in- 
dispensable because the hot drving winds that some- 
times sweep up from the South have been known to 
wilt a splendid field of grain overnight. Had wind- 
breaks been planted every quarter of a mile across the 
track of the prevailing wind, the force of these winds 
would have been greatly checked; water vapor would 
have been added to the moving air currents, and the 
force and drying effect of these damaging gales would 
have been greatly reduced. Investigators claim that 
twenty per cent of the agricultural land of the level 
Middle West could be advantageously planted with 
windbreaks running east and west and on account of 
the protection afforded by these belts the remaining 
eighty per cent of farm land would produce as much 
as the total area at the present time. The beneficial 
effects of these windbreaks in diminishing evaporation 
from plants and soil are clearly felt one rod to their 
lee for every foot in height. That is, a windbreak ten 
feet high would exert a‘decided influence in checking 
evaporation one hundred and sixty feet to the leeward. 
