314 FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



These, are the amounts of evaporation in one hour, and thoy show that the difference between -0 to 60 feet from 

 tlio woods and that between 280 to 320 feet was 43.4 35.0=8.4 <. c., and this is 24 per cent greater evaporation 

 at the three outer stations than at the three inner ones. 



I tn May 31 another trial was made in the town of Almond, to the south of an oak grove 80 rods square, in a 

 Held sowed to oats and wheat mixed. Here the first instrument was placed 20 feet from the margin of the grove, 

 the second 10 I feet distant, the third 200 feet, etc. The lirst two instruments stood upon ground seeded last year 

 to clover and timothy, but only timothy was growing where the second instrument stood. The grain upon the lield 

 had a fair stand whore the observations were made, and was about 4 inches high. There was at the time a fair wind 

 from nearly duo north and the day was clear. As in the former trials the ovaporometers were suspended at a height 

 of 1 foot above the ground ami were unsheltered in any way. The following table expresses the results obtained: 



. Cubic 



centimeters. 



At Station A, 20 feet from woods, the evaporation was 11. 1 



At Station H, 100 feet from woods, the evaporation was 14.3 



At Station C, 200 feet from woods, the evaporation was 15. 7 



At Station I), 300 feet from woods, the evaporation was '. 18.5 



At Station E, 400 feet from woods, the evaporation was 18.5 



At Station F, 500 feet from woods, the evaporation was 18.3 



From this table it will be seen there is an increasing amount of evaporation until 300 feet from the woods is 

 reached, and that beyond and including this the rate is practically the same, but at 300 feet the evaporation is 17.7 

 per cent greater than at 200 feet and 66.6 per cent greater than at 20 feet from the woods. 



Influence of a hedgerow on the rate of evaporation to the leeirard. On May 30 three of the instruments were 

 set np to the south of a very scanty hedgerow, consisting of a strip of blue grass l(i feet wide in which there are 

 scattering black and burr oaks from 6 to 8 feet in height, with a few attaining a height of 12 feet. This hedge has 

 very many open gaps in it, and the lirst instrument is set up behind a clump of six trees, spanning a length of 40 

 feet, there being a gap of nearly the same width on both sides of it. To the north of this, in the direction from 

 which the wind was blowing, there is a broad naked field being planted to potatoes, which has a width of about 80 

 rods, while the instruments hung over a field of oats in which the grain was about 4 inches high. After the instru- 

 ments were set up it became cloudy and sprinkled a very little at times, the wind being from a little east of north, 

 rather strong and chilly. Here again the instruments hung one foot above the surface, and the results obtained are 

 given below : 



Cubic 

 centimeters. 



At Station A, 20 feet from hedge, the evaporation was 10.3 



At Station B, 150 feet from hedge, the evaporation was 12. 5 



At Station C, 300 feet from hedge, the evaporation was 13.4 



Here it will bo seen the evaporation at 300 feet from the hedgerow was 3.1 c. c., or 30.1 per cent greater than at 

 20 feet distant, and at 150 feet the difference was 0.9 c. c., or 7.2 per cent less than 300 feet. It is evident, therefore, 

 that even such a hedgerow does exert an influence upon the rate of evaporation which is readily measured. 



INFLUENCE OF FORESTS UPON WATER AND SOIL CONDITIONS. 



(1) In consequence of deforestation, evaporation from tlie soil is augmented and accelerated, 

 resulting in unfavorable conditions of soil humidity and affecting unfavorably the size and con- 

 tinuity of springs. The influence of forest cover upon the flow of springs is due to this reduced 

 evaporation as well as to the fact that by the protecting forest cover the soil is kept granular and 

 allows more water to penetrate and percolate than would otherwise. In this connection, however, it 

 is the condition of the forest floor that is of greatest importance. Where the litter and humus mold 

 is burned up, as in many if not most of our mountain forests, this favorable influence is largely 

 destroyed, although the trees are still standing. (Pp. 130-137, Bui. 7.) 



(2) Snow is held longer in the forest and its melting is retarded, giving longer time for filtra- 

 tion into the ground, which also being frozen to less depth is more apt to be open for subter- 

 ranean drainage. Altogether forest conditions favor in general larger subterranean and less 

 surface drainage, yet the moss or litter of the forest floor retains a large part of the precipitation 

 and prevents its filtration to the soil, and thus may diminish the supply to springs. This is 

 especially possible with small precipitations. Of copious rains and large amounts of snow water, 

 quantities, greater or less, penetrate the soil, and according to its nature into lower strata and to 

 springs. This drainage is facilitated not only by the numerous channels furnished by dead and 

 living roots, but also by the influence of the forest cover in preserving the loose and porous structure 

 of the soil. 



Although the quantity of water offered for drainage on naked soil is larger, and although a 

 large quantity is utilized by the trees in the process of growth, yet the influence of the soil cover 

 in retarding evaporation is liable to offset this loss, as the soil cover is not itself dried out. 



