THE 



03RDEIN5' BULLETIN, 



5TR3IT5 5ETTLEnFrST5. 



Vol. II 



Issued August 5th, 1921 



No. 12. 



FORESTS AND THEIR RETENTION OF 



RAIN WATER. 



Fifty years ago a forester named Surell, published a study of 

 torrents in the High Alps (Etudes sur les torrents des Hautes- 

 Alpes 1870), a book that ran to a second edition two years later 

 under the editorshi]) of another, — ^E. ('ezanne. In this work the 

 re-aiforestation of bared slopes was advocated as a remedy against 

 landslips and denudation resulting from streams in flood. The 

 book led the way for reports, such as Demontzey's " Removal of 

 torrents in France by re-atforestation " (L'extinction des torrents 

 en France par le reboisement, 1894). Yet, though by the end of 

 the last century the principle had been recognised that forests pre- 

 vent this kind of destruction, many, some resenting forest regu- 

 lations, failed to realise their true importance: and therefore in 1900 

 a demonstration of the influence of forests upon the running off of 

 the rainfall was commenced in Switzerland by that country's 

 Central institute for the study of Forestry. For the demon- 

 stration two comparable valleys near Berne were selected ; one with 

 forest throughout, the other two-thirds in pasture. Rain guages were 

 installed; and guages put upon the streams that carry the water 

 .away. As no arrangements could be made for keeping records at 

 temperatures lielow freezing point, winter-observations were im- 

 possible : but after 18 years of observation in each year from April 

 16th to November 3()th, the results have been published by Dr. 

 Arnold Engler under the title of Untersuchungen neber den Ein- 

 fluss des Waldes auf den Stand der Gewasser. 



Tlie fate of the rain which fell, it is concluded, was : — 



to be run off through the streams . . 

 to be evaporated from off" the surface 



of the vegetation 

 to be evaporated from off the surface 



of the soil 

 to be taken u]) by the roots of the 



vegetation and thence passed 



back to the air by transpiration 



from the 

 forest 



60 parts 



5 „ 

 15 „ 



20 ., 



from the open 



60 parts 

 10 ., 

 24 „ 



6 „ 



100 parts 100 parts 



