62 PLANT SUCCESSION AND CROP PRODUCTION 



No comprehensive detailed studies of evaporation in this 

 state which can be correlated with plant growth have been 

 made. Dickey ('09) and Dachnowski ('11) have studied the 

 evaporation at Buckeye Lake, using the Ohio State University 

 campus lawn as unity. Sears ('16) has shown the evaporation 

 in the plant zone at the edge of a marsh in the Lake Erie region. 

 There are no other data available at present. 



For a comprehensive idea of evaporation and rainfall there 

 is the map of rainfall — evaporation ratios of Transeau (Figure 2, 

 p. 35), however. This gives a generalized picture of the effect of 

 air temperature, wind velocity and evaporation power of the air 

 in their effect on plant life. It was made by examining the forest 

 and prairie centers and finding a moisture index which best de- 

 scribed their climatic peculiarities. This chart shows that the 

 northeastern corner of Ohio, v/here Pinus strobus and other plants 

 of the northern evergreen center are known, has a rainfall evapo- 

 ration ratio of 100 to 110 percent. The greatest portion of the 

 state is covered by the deciduous forest and has a general ratio 

 of 80-100 percent, while in the edaphic prairies of Ohio the ratio 

 is between 60 and 80 percent. Further work on evaporation and 

 its relation to the vegetation centers is in progress. As soon as 

 this is published our understanding of the relation of forests and 

 prairies in Ohio will be greatly enlarged. The Erie Plain has 

 uniformly less than 34 inches of rainfall, the Ohio River region 40 

 inches. The heaviest rainfall occurs during the summer months. 

 June, July, and August. June has the greatest average rainfall with 

 4.13 inches. July is only slightly less rainy. The least monthly 

 rainfall is in October, averaging only 2.52 inches. 



The path of the storm track has an influence upon the direc- 

 tion of the prevailing winds. Over most of the state the prevailing 

 winds are from the southwest. Two notable exceptions, however, 

 are Cincinnati and Cleveland where the prevailing winds for the 

 year are from the southeast. The average hourly wind movement 

 is nearly nine miles. It varies with the season, being greater in the 

 winter and spring months than in the summer and fall months. 

 Near Lake Erie the average velocity is greater than in the central 

 and southern portions of the state. 



The humidity or the saturation deficit of the air is one of the 

 most important climatic influences upon plant and animal life. In a 

 state as large as Ohio and with such varied topography, the rate 



