American F'orest Congress 77 



during January, February, and March of the following 

 year had a run-off of approximately 37 per cent, of 

 the total precipitation, experienced a well-sustained 

 stream flow three months after the close of the rainy 

 season. The non-forested catchment area, which, 

 during December, experienced a run-off of 40 per 

 cent, of the rainfall, and which during the three fol- 

 lowing months had a run-off of 95 per cent, of the 

 precipitation, experienced a run-off in April (per 

 square mile) of less than one-third of that from the 

 forested catchment areas, and in June the flow from 

 the non-forested area had ceased altogether. 



Annual Rainjai,i, and Run-off on Forfstfd and Non- 

 FORSSTED Catchmxnt Areas in the San Ber- 

 nardino Mountains, California. 



Run-off Run-off in 



per square percentage of 



mile. precipitation. 



Acre feet. Per cent. 



731 28 



7S6 30 



904 36 



1,192 69 



"In conclusion, it may be said that although the 

 forest may have, on the whole, but little appreciable 

 effect in increasing the rainfall and the annual run-off, 

 its economic importance in regulating the flow of 

 streams is beyond computation. The great indirect 

 value of the forest is the effect which it has in pre- 

 venting wind and water erosion, thus allowing the soil 

 on hills and mountains to remain where it is formed, 

 and in other ways providing an adequate absorbing 

 medium at the sources of the water courses of the 



