AMERICAN FOREST CONGRESS 



75 



flicting that a definite answer to this question, having 

 the stamp of scientific accuracy, is not possible. 



"In a careful study of the behavior of the stream 

 flow on several small catchment areas in the San Ber- 

 nardino Mountains, it has been found that the effect 

 of the forest in decreasing surface flow on small 

 catchment basins is enormous, as shown in the follow- 

 ing tables, where three well timbered areas are com- 

 pared with a non-timbered one: 



PRECIPITATION AND RUN-OFF DURING DECEMBER, 1899. 



Run-off in 

 percentage of 

 precipitation. 



Per cent. 



3 

 6 

 6 



40 



"This is the stream discharge during a month of 

 unusually heavy precipitation. 



"At the beginning of the rainy season, in early 

 December, the soil on all four of these basins was 

 very dry as a result of the long dry season. The 

 accumulation of litter, duff, humus, and soil on the 

 forest-covered catchment areas absorbed 95 per cent. 

 of the unusually large precipitation. On the non- 

 forested area only 60 per cent, of the precipitation 

 was absorbed, although the rainfall was much less. 



