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Illinois Natural History Survey Bulletin 



Vol. 26, Art. 5 



size in Sampson was more nearly ade- 

 quate than the 1 256-miiacre size in this 

 unpastiired prairie; 4 species of the 13 

 found in the 64 plots of the 1 64-milacre 

 size attained a percentage of 50 or more. 

 These 4 species represented 30.77 per cent 

 of the number of species found in the 64 

 plots. .7. scfjparius occurred in all the 

 quadrats of the 1 64-niilacrc size. It is 

 evident that the 116- and the 1/4-miIacre 

 plots (C and D in table 10) gave good 



Frequency Values for Combina- 

 tions of Species. — In Sampson and 

 Phegley prairies, certain species of plants 

 occurred together in so many plots as to 

 call attention to the combinations. In 

 Sampson, the species in combination were 

 J ntlropot/ori sioparius, Solid/ii/n nemorali'!, 

 Hoiistoniti iiit/rirnns, and Dcsrnoiliiirn cil- 

 iiire. In Phegley, they were AiidropiD/on 

 Sioparius , Sniiiliu/o iicinurdlis , Distrindium 

 rilitirr, and Boiitil'iii/i lurlipeiidiila. The 



Table 12. — Frequency of occurrence of characteristic combinations of plant species, Samp- 

 son and I'he^ley hill prairies. 



• Combination in Sampson hill prairie: Andropogon uopariuj. Soiidaso nemoralis, Houstonia nigricans, and Dts- 

 modium citiarf. 



t Combination in Phegley hill prairie: Andropogon HOpariui. Solidago nemoralis, Desmodium ciliare, and Bouteloua 

 lurttpendula. 



distribution among species. In the one 

 (C), with a small number of plots and 13 

 species, 7, or 53.85 per cent, attained a 

 percentage of 50 or more; in the other 

 (D), with a large number of plots and 

 18 species, 7, or 38.88 per cent attained 

 a percentage of 50 or more. In Sampson 

 prairie, the frequency study showed, plots 

 of 1/64 to 1/4 milacre were of sufficient 

 size to give a satisfactor\- distribution of 

 species. 



Phegley Prairie. — Table 1 1 summa- 

 rizes the data for the frequencv study in 

 pastured Phegley prairie. As in Sampson, 

 the 1 256-milacre size was much too 

 small to give good distribution; only An- 

 dropogon scoparius attained a high fre- 

 quency percentage. The 1, 64-milacre 

 size did not give good distribution of spe- 

 cies; only two, A. scoparius and SoUdago 

 nemoralis, attained percentages of 50 or 

 more. These species represented 13.33 per 

 cent of the total found in the 64 plots of 

 this size. In Phegley prairie, the fre- 

 quency study showed, plots of 1/16 to 

 1/4 milacre were of sufficient size to give 

 a satisfactory distribution of species. 



frequency values for these combinations 

 of species are summarized in table 12. For 

 the two larger plot sizes, 1/4 and 1 mil- 

 acre, the sample was the 9-milacre square. 

 For the 1/64- and 1/16-milacre sizes, 

 the sample was the central milacre of the 

 9-milacre square. For the 1 /256-milacre 

 size, the sample was 1/4 milacre, the 

 northwest quarter of the central milacre. 

 If the 1 4-milacre size had been studied 

 in only the central milacres, the percent- 

 age of occurrence of the characteristic 

 combinations for both Sampson and Pheg- 

 le\ would have been 100. 



Wherever one or more combinations of 

 species can be discerned in any particular 

 type of vegetation, the combinations can 

 serve as a criterion of adequacy of plot 

 size. In Phegley prairie, the 1/16-milacre 

 size was obviously too small to give a 

 fairly high frequency of occurrence for 

 the characteristic combination; in Samp- 

 son prairie, the 1 '64-inilacre size was too 

 small. 



Frequenc\ of occurrence of character- 

 istic combinations of species has been used 

 as a test of the adequacy of size of sam- 



