FlfTH NATIONAI, CONSERVATION CONGRESS 303 



With the exception of those countries which have naturally a humid climate, 

 like Great Britain or the Netherlands, the countries with a forest area of only 30 

 per cent or less show usually to a marked degree bad climatic conditions, with 

 prolonged droughts, frosts, and alternating floods and low water, as a result of 

 the reduced forest area. Portugal, with a forest area of only 3J4 per cent of 

 the total; Spain, with 16 per cent; Greece, with 13 per cent; Turkey, with less 

 than 30 per cent, and Italy, with 14 per cent, are good examples. 



The facts established with regard to the effect of forests in wide plains of 

 continents, especially in the path of moist winds, allow the following practical 

 deductions to be drawn : 



1. Forests must be protected not so much in localities which already suffer 

 from lack of moisture as in regions which lie in the path of prevailing winds 

 and are still abundantly supplied both with ground water and precipitation. 

 In the dry regions large bodies of forests may have the opposite effect upon the 

 available water supply. There only forests growing along rivers may contribute 

 to the humidity of the region. There rows of trees or windbreaks surrounding 

 fields and orchards, by preventing the drifting of the snow and decreasing the 

 activity of the wind, will act more as conservers of moisture in the soil than 

 solid bodies of timber. Therefore, the care with which forests should be pro- 

 tected in the eastern half of the United States must increase from north to 

 south and from west to east. 



3. In the Atlantic plain and southern Appalachians, which are the gateway 

 for the prevailing winds from the Gulf of Mexico and the Atlantic Ocean, forests 

 must be especially maintained — 



(a) On moist soils, provided the excess of water or the substances contained 

 in.it do not prevent their development, because the moister the soil on which 

 forests grow the more moisture they evaporate. For this reason swamps, since 

 they contribute less to the moisture contents of the air than crops or forests and 

 lose considerable water by surface run-off, must be drained, as by doing this an 

 increase of the evaporation at the expense of surface run-off may be secured. 



(b) On sandy soils. Forests on sandy soils readily absorb water through 

 the roots and evaporate it into the atmosphere. Denuded of forest cover, sandy 

 soils readily absorb rainwater which percolates into the ground and often reaches 

 the sea by underground channels without being returned to the atmosphere. 



(c) On steep slopes and rocky places; the removal of forests on such places 

 inevitably leads to an increase in the surface run-off and to a corresponding de- 

 crease in local evaporation. 



3. If clearing of the forest is a necessity it should be done only under con- 

 dition that the cleared land is to be devoted to intense cultivation, as, after forests, 

 crops contribute most to the moisture of the air. The highest organic production, 

 therefore, is in harmony with the safeguarding of the humidity in the regions 

 which lie in the path of the prevailing winds. Cleared land that becomes waste 

 or poor pastures or grows up to weak vegetation, means so much evaporation 

 lost to the passing air currents. 



