Forest Influences. 



21 



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 rain- 

 fall was much less. 



RAIN-FALL AND RUN-OFF D^^RING JANUARY, FEBRUARY AND MARCH, 



1900. 



The most striking feature of this table as compared with the 

 previous one is uniformly the large run-off as compared with the 

 rainfall. This clearly shows the enormous amount of water 

 taken up by a dry soil, either forested or non-forested, as com- 

 pared with one already filled to saturation. During the three 

 months here noted, on the forested basins about three-eighths of 

 the rain-fall appeared in the run-off, while on the non-forested 

 areas nineteen-twentieths appeared in the run-oft". 



The above table clearly shows the importance of forests in 

 sustaining the flow of mountain streams. The three forested 

 catchment areas, which, during December, experienced a run-off 

 of but 5 per cent of the heavy precipitation for that month, and 

 which during January, February and March of the following 

 year had a run-off of approximately 37 per cent of the total pre- 

 cipitation, 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 following months 



*640 acre-feet equal 12 inches of precipitation over a square mile. 



