American Forest Congress 297 



ideal conditions are those which are densely forested 

 and can, therefore, act as conservators of the water 

 supply with the least artificial aid. 



Forests aid in controlling the run-off. Compare 

 two tracts similar in all other respects, but the one 

 densely covered with a forest canopy, while the other 

 has been denuded of such protection. In the first 

 case the forest cover, with its attendant conditions of a 

 more granular and porous soil, its humus and leaf 

 mould, holds back precipitation instead of letting it 

 run off as rapidly as it would otherwise do. The 

 snows of winter cover the ground with comparative 

 evenness, so that it is protected from rapid melting 

 when the sudden warm periods come. The moisture, 

 moreover, instead of disappearing rapidly as surface 

 run-off, goes very largely into the ground to appear 

 in the form of springs, perhaps months later, as seepage 

 run-off. The same is true of the summer rains. In- 

 stead of the precipitation resulting from this cause 

 converging rapidly into a great torrent sweeping 

 everything from before it, the moisture goes into the 

 ground to return again as run-off when it is more 

 particularly needed, the otherwise torrential stream 

 becoming well sustained and perennial. 



From deforested tracts the run-off is much more 

 likely to be beyond human control. Great floods made 

 up from the converging streams carrying logs and 

 debris of all kinds before them, sweep irresistibly 

 down the river valleys, taking with them diversion 

 dams, gates, power plants, and destroying what they 

 cannot carry away. 



Then again, in a well forested tract, if over-grazing, 

 with its attendant ills, has not been tolerated, there is 

 usually a dense undergrowth, which retards the run- 

 off during rapid melting or after violent storms. Its 



