422 Forestry Quarterly. 



Hence, the farther from the ocean the greater is the part of the 

 air moisture contributed by evaporation from the land." 



The amount of this evaporation from land has been, by Bruck- 

 ner, calculated for the whole earth as one quarter of the evapora- 

 tion from water surfaces, and only 7 per cent, of the evaporation 

 of oceans, equivalent to 2.8 inches, according to the same in- 

 vestigator, is carried to land, so that even the land area peripheral 

 to the ocean secures only a little over 20 per cent, of its precipita- 

 tion from the vapors of the ocean, the balance being secured from 

 the land evaporation, while interior basins rely entirely on the 

 latter. 



The moisture which is carried by the winds into the interior 

 of vast continents, thousands of miles from the ocean, is almost 

 exclusively due to continental vapors and not to evaporation from 

 the ocean. 



What Bruckner figures for the entire world is found by studies 

 of specific drainage areas, for instance by Nipher for the rainfall 

 of Missouri, the larger portion of the precipitation being not re- 

 turned to the sea but evaporated back from the land to the atmos- 

 phere. Lindsay corroborates these conditions for the discharge 

 of the Mississippi in Louisiana. 



Observations and arguments for establishing the greater evapor- 

 ative power of forest areas are then brought, Henry, Hohnel, and 

 Otozky being cited to show that forest areas furnish more mois- 

 ture to the atmosphere than water surfaces — data which we think 

 are open to doubt. They are believed conclusive at least for for- 

 ests in the plains. 



The practical deductions are especially interesting. 



"Forests must be protected not so much in localities which al- 

 ready suffer from lack of moisture as in regions which lie in the 

 path of prevailing winds and are still abundantly supplied with 

 ground water and precipitation", hence the care of forests in the 

 Eastern United States should increase from north to south, and 

 from west to east. In dry regions forest cover may have dimin- 

 ishing effect on available water supply, except along rivers or in 

 the shape of wind breaks. This seems a doubtful conclusion, as 

 well as the following: "Forests must be specially maintained on 

 moist soils because the moister the soil on which forests grow 

 the more moisture they evaporate. For this reason swamps. 



