80 JOURNAL OF FORESTRY 



SOIL, WATER, AND CLIMATE 



Since 1900 the Swiss forest experiment station 

 Forests has been studying the influence of a forest cover 



and on streamflow in two neighboring and compar- 



Streamflozv able watersheds, one of which was 97 per cent 



and the other 29 per cent forested. Actual 

 measurements show that forest soils in good condition absorb the bulk 

 of the precipitation, which later runs ofT subterraneously ; while in soils 

 not so protected there is an immediate surface run-ofif accompanied 

 by erosion and gullying, particularly on steep, turfed slopes. This 

 beneficial influence of the forest is due to the permeability and porosity 

 of its soil rather than to the great hygroscopicity of the humus and 

 moss cover, which if too abundant may actually, after becoming sat- 

 urated, have the opposite efifect and stimulate surface run-ofif. During 

 periods of rapid snow melting both the peak of the flood and the total 

 discharge were less from the well-forested than from the poorly for- 

 ested watershed. The run-ofif from the former after heavy or tor- 

 rential downpours was only a third to a half of that from the latter. 

 After prolonged rains the influence of the forest depended on whether 

 the soil was comparatively dry or saturated at the beginning of the 

 wet spell. In any event, however, erosion is less on well forested water- 

 sheds, and the flood waters from them, having a lower velocity and 

 carrying less detritus, do less damage. During periods of prolonged 

 drought the stream from the well forested watershed never went dry, 

 while that from the poorly forested one often did so for a month or 

 two at a time. All of these dififerences would have been more marked 

 if the well forested watershed had not had appreciably steeper slopes 

 than the other, and if the latter had been completely deforested. 



S. T. D. 

 Huffel, G. Le mouvcmcnt forcsticr a I'etranger: station de recherches 

 forestieres suissc. Rev. Eaux et forets. 58:249-254. 1920. 



Dry wood contains about 50 per cent carbon 



Chlorophyll and air about 0.3 per cent carbon dioxide. For 



Assimilation and a forest of Scotch pine to produce 5 cubic meters 



Water of wood per hectare per year, it is therefore neces- 



Requirements of sary for the chlorophyll in the leaves to come into 



Scotch Pine contact with 7,715,000 cubic meters of air. This 



means that during the 1,200 hours of insolation 



in the period of vegetative activity between May 1 and September 1, 



the leaves must absorb every second a volume of air equal to nearly 



one-fifth of their own volume ; or, in other words, that the openings 



in the chlorophyll tissues must fill and empty themselves of air at least 



