892 JOURNAL OF FORESTRY 



I. Forests and Slrcaiit-fluz'^'.—li has been proved that the effect of 

 forests upon streams in level countries is unimportant, but in hilly and 

 mountainous countries they are conservers of water and tend to main- 

 tain a steady flow of water in the streams. 



In the mountains the greatest loss of rain water is through surface 

 run-off (water that washes oft' the surface of the ground) ; and the 

 most important influence of a forest cover is in reducing this. It is 

 stated that the amount of water saved in this way by the forest is 20 

 per cent to 35 per cent, and often more with higher altitudes. 



The reasons why the forest is able to check surface run-off and save 

 portions of it to the soil are, first, the trunks and the underbrush in 

 the forest offer mechanical obstruction ; second, the litter of the forest 

 floor checks rapid surface drainage of the water and also acts as a 

 sponge ; and, third, the network of deeply penetrated roots, living and 

 decayed, make the forest soil more porous and permeable ; hence the 

 water sinks into it more readily. 



It is evident that the ability of the forest to check surface run.-off is 

 greatest when the forest is dense and when the ground beneath it is 

 covered with an unbroken leaf litter. 



It must be borne in mind, however, that when water is precipitated 

 from the clouds, a portion of it is prevented from reaching the ground 

 through interception by the leaves, branches, and trunks of the trees. 

 This intercepted portion varies according to the tree species and the 

 density of the woods. According to Bavarian investigations, it averages 

 23 per cent of the total rainfall. So, after a rain, we often find that 

 water continues to drip from the leaves and twigs for hours. 



With this knowledge of the different factors which tend to influence 

 the amount and the rapidity of running water in forest-clad watersheds, 

 we are in a position to understand the relation of forests to stream- 

 flow. 



In forested regions, rain-water is conserved in such a way that it 

 is allowed to drip slowly down. So we find that in such regions 

 streams do not rise high immediately after rains and do not dry up 

 when there is no rain, and there is always a great abundance of springs 

 which go to feed such streams. Forests and forest soil are like large 

 reservoirs for the conservation of rain-water for stream-flow. 



Forests regulate stream-flow 1)y conserving not only water, but also 

 snow. That forests retard the melting of snow has been demon- 

 strated in a series of observations carried on at Moscow. Results. show 

 that the period of snow melting within forests is from 26 to 57 days, 

 while snow in the open disappears within six or seven days. The 



