INTERCEPTION. 



131 



cepted by tlie foliage and at once retnrned to the atmosphere by evap- 

 oration ; if, however, the rain continues, although fine, the water will 

 run off at last from the foliage and along the trunks. And this amount, 

 of which the rain-gauge takes no acconnt, rei)resents, according to 

 measurements from the Austrian stations, from 8 to 14 per cent, thus 

 reducing considerably the loss to the soil l>y interception. 



While the careful measurements at the Swiss statious in a twelve 

 years' average show the interception in a larch forest as 15 per cent, in 

 a spruce forest 23 per cent, in a beech growth 10 per cent, the flgures 

 for the Prussian stations are for beecli growth 24: per cent, for spruce 

 at various stations 22 per cent, 27 per cent, and 34 per cent, respectively. 

 Altogether, for the rainfall conditions of the countries cited, a dense 

 forest growth will, on the average, intercept 23 per cent of the precipi- 

 tation ; but if allowance be made for the water running down the trunks, 

 this loss is reduced to not more than 12 ijer cent.* (See page 100 of this 

 bulletin.) 



According to A. Matthieu's observations during eleven years at Oinq- 

 Franchees (Meteorologie comparee agricole et forestiere, 1878), only 8.5 

 X)er cent were retained by crowns (5.84 per cent in winter, 11 per cent 

 in summer). The more exact observations of Eiegler are compiled as 

 follows : 



Species. 



Beech. 

 O-ik... 

 Maple 

 Spruce 



Bain on 



Clown. 



Liter. 

 20, 021 

 24, 273 

 30, 901 

 12, 014 



Fell 



through 



the crown 



upon soil. 



Liter. 



17,008 



17, 873 



26, 384 



4,793 



Run off 

 trunk. 



Liter. 



3,343 



1,387 



2,198 



165 



Reached 

 soil alto- 

 gether. 



Liter. 

 20. 411 

 19, 260 



28, 582 

 4,958 



Lost by 



evapor.a- 



tion. 



Per cent. 

 21.8 

 20.7 

 22.5 

 58.8 



Percent- 

 age of rain 

 reaching 

 soil alto- 

 gether, 



78.2 

 79.3 

 77.5 

 41.2 



The results ibr spruce become vitiated by the fact that large aiuounts 

 of water run off from the tips of the branches, which have an inclina- 

 tion away from the trunk, and which could not be measured. 



The intensity of the preci]»itatiou and the condition of folinge have 

 much to do with the amounts reaching the soil, so tliat sometimes prac- 

 tically all the rain reaches it and sometimes hardly any. 



The amount of interception in the open growths which characterize 



*The maxinmui rainfall ol>seive<l in rJermany is 4 iucbes in twenty-four hours and 

 2 iiiflie8 in one hour. In iSwit/A-rland there has bcou recorded a rainfall of 18 inches 

 in twenty-four hours, and 2k inches in three-iiuarters of an hour. This would equal 

 5, (MM) frallous per acre. Of such falls the foliage will retain only an inappreciable 

 amount. Intensity of rainfall in the United .States becomes clear from a few records : 

 Paterson. N. J., li inches in eight minutes; Sandy Spring, Md., 5 inches in two and 

 one-half hours; Clear Creek, Nebr., 4,50 inches in one hour and twenty-seven min- 

 utes; Castroville, Tex., 5.80 inches in twenty-four hotirs; Ellsworth, N. C., 13 inches, 

 of which 9 inches in three and one-half hours; and rainfalls from IJ to 4 inches per 

 twenty-four hours are quite frequently reiiorted in almost every month, especially in 

 the Western States. 



