August, 1955 



EvERs: Hill Pr.\iries of Illinois 



391 



pie in one study known to the writer : 

 the forest stud\' bv \"estal iS: Heernians 

 (1W)._ 



Species-Area Curve. — A species-area 

 curve can be constructed from data ob- 

 tained from the species list for the various 

 plot sizes. The maps of the central mil- 

 acres, tigs. 8 and '^, furnished the data for 

 deri\ing average numbers of species in 

 quadrats of 1 256-, 1/64-, and 1/16-mil- 

 acre sizes. Species lists, compiled by 1/4- 

 milacre units, for each of the 9-milacre 

 squares furnished the data for computing 

 the averages for quadrats of 1/4- and 1- 

 milacre sizes. The total number of spe- 

 cies found in the '^-, 25-, 40-, 50-, 65-, and 

 75-milacre areas provided the figures for 

 the larger plot sizes. These data are 

 shown in table 13. 



When the data are plotted on semiloga- 

 rithmic paper, the resulting curves are 

 S-shaped, hg. 13. From this type of curve, 

 certain reference areas can be determined 

 with the method described by \'estal 

 (19491. These are (1) the smallest rep- 

 resentative area, (2) the minimum area 

 for assignment to type, after this referred 

 to briefly as minimum area, and (3) the 



Table 13. — Numbers of plant species in 

 plots of vari, us sizes, Sampson and Phegley 

 hill prairies. 



* The average number of species per quadrat (or plot 

 sizes of I milacre and smaller; total number of species in 

 larger quadrats. 



area of fair-sized stand. The smallest rep- 

 resentative area (Ar) is the smallest one- 

 piece area having some claim to be rep- 

 resentative. It is the eftecti\e plot-size 

 of Vestal iSc Heermans (1945). The min- 

 imum area (Am), a plot-size that is 

 large enough to include all the important 



AREA (MILACRES) 



Fig. 13. — Species-area curves for Phegley (grazed) and Sampson (ungrazetl) hill prairies. 

 hx, smallest representative area; ."^m, minimum area for assignment to type; Af, fair-sized stand. 



