May, 1911.] Evaporation Gradient in a Woodlot. 
347 
A NOTE ON THE EVAPORATION GRADIENT IN A 
WOODLOT.* 
Malcolm G. Dickey. 
The subject of evaporation has received much attention 
within the past few years. Very significant results have been 
obtained from the standpoint of plant phvsiologyy and ecology" as 
well as meteorology". The question in general, as to its relation 
to plant societies, has been discussed in connection with an earlier 
paper on evaporation in a local bog habitat. f 
More recently, further work has been carried on in the same 
habitat to ascertain the evaporation at different heights,! and in 
this connection, it was thought desirable to obtain similar data as 
to the evaporation gradient in a wooded area. 
Owing to the intimate relation between forests, climate, and 
waterflow, and the important bearing of the subject upon our 
national conservation policy, forest meteorology" has been made 
the subject of a very' careful study. Of especial value are the 
results of investigations, extending over a number of y r ears, 
conducted by the German Forest Service. A summary^ of these 
results reveals the fact that the average evaporation from the 
ground within woods is about 44% of that within the fields. 
This reduction of evaporation is accounted for by" a greater relative 
humidity due to lower temperature by shade, breaking of winds, 
and the protection of the soil litter. The forest, though perhaps 
less effective in adding moisture to the air than some other ty r pes of 
vegetation formations, gives off a more uniform supply, and con- 
tinues to do so when elsewhere the saturation deficiency" of the air 
is relatively" high. 
Although, some general conclusions have been presented as to 
the vertical gradient of temperature and humidity in the forest, 
there seem to be no similar data for evaporation. The experiment, 
discussed here, was undertaken with a view to gaining some light 
on this phase of the subject. The station selected was located in 
a woodlot about ten miles north of Columbus. The predom- 
inating species is beech, (Fagus americana), with a mixture of 
white oak, (Quercus alba), maple (Acer Saccharum), and hickory" 
(Hicoria ovata). The stand is fairly dense, and the ground is 
*Contribution from the Botanical Laboratories of Ohio State Univer- 
sity, No. 63. 
(Dickey, M. G. Evaporation in bog habitat. Ohio Naturalist 10: 
17-23. 1909. 
(Dachnowski, Alfred. Vegetation of Cranberry Island (Ohio), and its 
relation to the substratum, to temperature, and evaporation. Bot. Gaz. 
51. 1911. 
§Harrington t , M. W. Review of forest meteorological observations. In 
Forest Influences. U. S. Dept. Agr. Div. of Forestry. Bull. 7. 1893. 
