EVAPORATION. 



65 



preventing evaporation than the forest itself. 80 great 

 is the power of the latter that direct observations made 

 in Bavaria and Prussia showed that evaporation from 

 a free surface of water in the forest was onlv 4:0 per 

 cent of that in the open. 



The presence or absence of leaf mold has a powerful 

 effect on the amount of evaporation from forest soil. 



Fig. 42.— a snow bank evaporating. San Gabriel Mountains, California. 



The experiments of Dr. Eberma^'er, a famous German 

 forest meteorologist, showed that evaporation from 

 forest soil without a hiyer of mold was 47 per cent 

 of that from soil in the open, while with a layer of 

 mold it was less than half as much, or 22 per cent. 

 The greater the altitude above the sea the greater is the 

 effect of the forest in preventing evaporation. This is 

 a powerful reason for preserving mountain forests at 



