May, 1911.] Evaporation Gradient in a IVoodlot. 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 physiology, 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, J 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 years, 

 conducted by the Gennan 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 types of 

 vegetation formations, gives off' a more unifonn supply, and con- 

 tinues to do so when elscAvhere 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. 



jDiCKEY, M. G. Evaporation in bog habitat. Ohio Xatur,\list 10: 

 17-23. 1909. 



JD.^CHNOwsKi, Alfred. Vegetation of Cranberry Island (Ohio), and its 

 relation to the substratum, to temperature, and evaporation. Bot. Gaz. 

 51. 1911. 



§Harrin'Gtox, M. W. Review of forest meteorological observations. In 

 Forest Influences. U. S. Dept. Agr. Div. of Forestry. Bull. 7. 1893. 



