138 
IOWA ACADEMY OF SCIENCE Vor,. XXVII, 1920 
Hall and Maxwell,^ Tourney,® Bray,® and Schwartz have 
confined their studies more particularly to the influence of forests 
upon stream flow, although Bray includes studies concerning the 
general influence upon climate and the relations of various plant 
associations to soil moisture. Hall and Maxwell present very 
interesting information regarding the flood problem along the 
courses of various streams in the United States. They show 
that, with certain exceptions, the tendency is toward increased 
floods and that this has a relation to the forest cover especially 
on the slopes of the drainage area, which slopes are considered by 
them as making up the vital part of a water-shed. Zon arrives 
at a similar conclusion. 
None of these writers, however, has dealt to any great extent 
with direct measurements of soil moisture in forested areas, to 
determine specifically the extent to which forests control the 
movement of soil water after the surplus has passed on as run- 
off, and the effect that this influence may have as regards the 
water table throughout a region in general. It is true that Zon 
does present extensive information to show that there is a 
direct relation between forests and stream flow, seepage into the 
soil, flow of springs, etc., and he establishes further that there is 
an important relation existing between forests and the water table. 
The importance of this latter problem has been more fully pre- 
sented by McGee.® He shows that the level of the water table 
throughout the United States has lowered appreciably within the 
past fifty years, having dropped 12.5 feet in Iowa. He shows 
also the importance of forested areas in connection with this 
lowering. 
It was with these considerations in mind that the studies here 
discussed were undertaken. It is recognized that the work done 
is of more or less preliminary nature, and that the results of 
various phases at least are to be interpreted as indications of 
certain deductions rather than as permitting final conclusions. 
The work consisted of two lines of investigation: first, the de- 
termination of the rate of evaporation for forested and open 
4 Hall, Wm. H., and Hu Maxwell, Surface conditions and stream flow: U. S. 
Dept. Agric., Forest Service, Circular 176, January, 1910. 
5 Tourney, James W., The relation of forests to stream flow: Reprinted from U. 
S. Dept, of Agric., Yearbook for 1903. 
6 Bray, Wm. L,., The timber of the Edwards Plateau of Texas; its relation to 
climate, water supply, and soil: U. S. Dept. Agric., Bur. Forestry, Bull. 49, 1904. 
7 Schwartz, G. Frederick, The diminished flow of the Rock River in Wisconsin and 
Illinois, and its relation to the surrounding forests: U. S. i'ept. Agric., Bur. For- 
estry, Bull. 44, 1903. 
8 McGee, W J, Wells and subsoil water: U. S. Dept. Agric., Bur. Soils, Bull. 92, 
1913. 
