August. 1955 



EvERS: Hii.i. Prairies of Illinois 



389 



Hedeoma hispida, R. aroinatica, and Ger- 

 ardia (possibly G. aspera). The 75-niil- 

 acre unit minus the lO-milacre border 

 strip contained 29 species. The 75-mil- 

 acre unit contained 3i species. 



Frequenc\' of Occurrence of Spe- 

 cies. — The f requenc) , or repeated occur- 

 rence, of plant species in Phegley and 

 Sampson prairies was determined from 

 species lists of each of the following plot 

 sizes: 1 256-, 1/64-, 1 16-. 1/4-, and 

 1-milacre. Although the 1 256-milacre 

 unit was not marked in the field, data for 

 plots of this size were obtained from maps 

 of the mapped central milacre of both 

 Sampson and Phegley prairies, figs. 8 and 

 9. On such maps the northwest quarter 



of the milacre was divided into 64 equal 

 quadrats an\l, from these, species lists were 

 compiled. The metric equivalent of this 

 quadrat size is 0.0156 square meter. For 

 any given plot size the frequency was ex- 

 pressed as a percentage computed b> divid- 

 ing the number of quadrats in which the 

 species occurred by the total number of 

 quadrats of that size employed. 



Sampson Prairie. — Table 10 summa- 

 rizes the data for the frequency study in 

 unpastured Sampson prairie. It is evi- 

 dent that the 1 256-milacre size was too 

 small for use in ecological studies of Illi- 

 nois hill prairies; onh' one species, .-i ii- 

 dropognu scoparius, attained a high per- 

 centage of occurrence. The 1 6-(-milacre 



Table 11. — Frequency of occurrence of plant species in plots of five sizes. Phegley hill 

 prairie. 



Species 



Size A 



(1/256 

 Milacre, 

 0.01S6 

 Sqiare 

 Meter) 



Num- 

 ber 

 of 

 Plots 



.indropogon scoparius 

 SoUda%o nemoralis . . 



Desmodiiim ciliare 



Boutelotia curtipendula . . . 



Lespedeza slipulacea 



Gerardia gatlingerii'.) . . . . 

 Pelalostemutn purpureum . 



Houslonia nigricans 



Lespedeza capitata 



Euphorbia corollala 



Juniperus virginiana 



Senecio ptaltensis 



Cassia fasciculata 



Poly gala verticillata 



Panicum scriknerianum. . . 



Linum sulcatum 



Aster patens 



Eragrostis spectabitis 



Andropogon gerardi 



Lecidea spp 



Rhus copallina 



Kuhnia eupatorioides 



Gerardia aspera('.) 



Poa pralensis 



Hedeoma hispida 



Rueltia liumilis 



42 

 2 

 3 

 3 

 9 

 3 

 3 

 1 

 3 



Per 



Cent 



of 

 Plots 



89.1 



65.6 



3 1 



4.7 



4.7 



14.1 



1.6 



Size B 



n 64 



Milacre, 

 0625 

 Sqcare 

 Meter) 



Num- 

 ber 

 of 



Plots 



// species 

 64 plots 



64 



59 



8 



21 



29 



21 



13 



11 



7 



6 



3 



1 



3 



2 



Per 



Cent 



of 



Plots 



100.0 



92.2 



12.5 



32.8 



45.3 



32.8 



20.3 



17.2 



10.9 



9.4 



4.7 



1.6 



4.7 



3.1 



4.7 



Size C 



n 16 



Milacre, 



0.25 

 Square 

 Meter) 



Num- 

 ber 

 of 

 Plots 



Per 



Cent 



of 



Plots 



16 



16 



6 



9 



12 



13 



10 



10 



6 



5 



2 



1 



2 



2 



100 

 100.0 

 37.5 

 56.3 

 75.0 

 81.3 

 62.5 

 62.5 

 37.5 

 31.3 

 12.5 

 6.3 

 12.5 

 12. S 



19.4 



15 species 

 64 plots 



15 species 

 16 plots 



Size D 



(1 4 

 Milacre, 



1.01 

 Sqcare 

 Meters) 



Num- 

 ber 

 of 

 Plots 



36 



36 



33 



33 



31 



30 



29 



27 



18 



11 



10 



9 



7 



4 



4 



3 



3 



2 



1 



1 



1 



1 



1 



1 



1 



1 



Per 

 Cent 



of 

 Plots 



100.0 

 100.0 

 91.6 

 91 

 86 

 88 

 80 

 75 



50.0 



30.6 



27.8 



25.0 



19.4 



11 1 



11.1 



8.5 



8.5 



5.6 



2.8 



2.8 



2.8 



2.8 



2.8 



2.8 



2 8 



Size E 



(1 



Milacre, 



4.05 

 Square 

 Meters) 



Num- 

 ber 

 of 



Plots 



26 species 

 36 plots 



Per 



Cent 



of 



Plots 



100.0 



100.0 



100.0 



100.0 



100.0 



100.0 



100.0 



100.0 



77.8 



55.6 



66.7 



77.8 



44 4 



33 3 



33.3 



22.2 



22.2 



22 2 



U " 



11 



11 



11 



II 



11 



II 



n 



36 species 

 9 plots 



