76 



Indiana. Their results are combined and summarized in Figure 5. 

 This diagram shows the relative evaporation near the surface of the 

 soil, the standard of comparison being the evaporation in a maple- 

 beech climax forest, where evaporation is relatively low. The aver- 

 age daily amount, in c.c, shows that there is a progressive increase in 

 evaporation as follows: 8.1 c.c. in a maple-beech forest, 9.35 c.c. in 

 the oak-hickory upland forest, 10.3 c.c. in an oak dune forest, 11.3 c.c. 

 in a pine dune forest, and an increase to 21.1 c.c, on the cottonwood 

 dunes. This expressed on a percentage basis is, in inverse order, re- 

 spectively 260 per cent, in the cottonwoods, 140 per cent, in the pines, 

 127 per cent, in the oak dunes, 115 per cent, in the oak-hickory for- 

 est, and 100 per cent, in the maple-beech forest. 



20 ^0 60 eo 100 120 r40 160 160 200 22Q gdO 260 260 



Intensity of evaporation 



Sta. A. Cottonwood dunes 



Sta. B. Pine dune 



Sta. C. Oak dune 



Sta. D. Oak-hickory 



Sta. E. Maple-beach forest 



Pig. 5. Diagram showing the relative rate of evaporation in different kinds of 

 forest in northern Illinois and Indiana. [Data from Fuller ('11) and McNutt and 

 Fuller ('12).] 



Shimek ('10, '11) has made valuable observations on the relative 

 rate of evaporation on the prairie of western Iowa. He used the open- 

 pan method in four representative habitats. His results show very 

 clearly that the rate of evaporation is much greater in exposed places 

 than where there is shelter from the sun and wind. I have put his 

 data in a form comparable with those which have just been discussed 

 (Fig. 6), and have made the cleared field area, Station 4, the standard 

 of comparison, as it more nearly approaches the standard used at 

 Charleston and by others. Station 3 is on a high bluff, exposed to the 



Intensity of evaporation . 



200 



Sta. 3. Open, much exposed prairie 

 vegetation 



Sta. 1. Open, exposed slope of bluflf, 

 prairie 



Sta. 4. Open, cleared area, partly pro- 

 tected 



Sta. 2. Bur-oak grove, protected 



Fig. 6. Diagram of relative evaporation in prairie and forest habitats, in western 

 Iowa. (Data from Shimek.) 



