.^80 



Illinois Natural History Survey Bulletin 



Vol. 26, Art. 5 



64 small squares of 1 64 milacrc (ap- 

 proximately 6.25 square decimeters) to 

 facilitate mapping. These small units 

 were combined in working o\er the data 

 to give 1/16-, 14-, and 1-milacre plots. 

 The central milacre quadrat in the Phcg- 

 ley prairie was mapped, fig. 8, and tiic 

 shoots in this milacre were counted on 

 October 9 and 10, 1951, by the writer 



each with an area of 5 milacres and five 

 each of 10 milacres. Species lists were 

 then compiled for the staked areas of each 

 prairie by units of 1/64, 1/16, 1/4, 1, 3, 

 5, 9, 10', 25, 50, and 75 (30.?. 5 square 

 meters) milacres. 



From data obtained from the staked 

 areas, it w-as possible to determine the 

 number of plant species and number of 



33' 



a. 

 o 



_i 

 vt 



z 



o 

 o 



SAMPSON (UNGRAZED) 



PHEGLEY (GRAZED) 



Fig. 10. — .Xfrangcinciit of plots and strips in two hill piairies. Each shaiied square repre- 

 sents the mapped central milacre of a 9-milacre K'''''- 



with the assistance of Dr. A. G. V'estal ; 

 the central milacre in Sampson prairie was 

 iTiapped, fig. 9, and the shoots were 

 counted on October 15 and 16, 1951, by 

 the w-riter. In addition, a list of plant 

 species was made for each 1 4 milacre in 

 the other 8 milacres of each of tlie 9-mil- 

 acre grids. 



In order to find the increase in number 

 of species with an increase in area, the 

 writer staked a 25-milacre square and a 

 50-milacre rectangle in each of the two 

 prairies, fig. 10. In Phegley, the 25-mil- 

 acre square was downslope from the nortli 

 half of the 50-milacre plot, the half that 

 included the 9-milacre square. In Samp- 

 son, because of the proximity of woodland, 

 the arrangement could not be made iden- 

 tical with the arrangement of plots in 

 Phegley: the 9-milacre square was inside 

 the 25-milacre square ; the south half of 

 the 50-milacre rectangle was downslope 

 from the 25-milacre square. The staked 

 25- and 50-milacre plots were divided into 

 strips 6.6 feet wide, making five strips 



shoots in plots of various sizes; for each 

 species, the frequency of occurrence in 

 plots; for each of the several grass spe- 

 cies, the area covered or ground space of 

 plants; and, for all species collectively, the 

 estimated number of plants per unit of 

 area and the available space per plant. 

 Comparisons between pastured and un- 

 pastured hill prairie were made. From 

 the data it was possible to construct a 

 species-area curve and from the curve to 

 find the sizes of certain reference areas, 

 as will be explained later in this section. 

 Method of Coujiting Plant Units. — 

 For plants other than grasses, each shoot 

 that appeared above the ground surface 

 and was without obvious connection to 

 another shoot was counted as one unit, or 

 individual. For example, each single 

 rosette of Solidago nemoralis was counted 

 as one individual ; each shoot of Honsto- 

 nia nigricans, Petalostemum purpureuni , 

 and Desmodium ciliare was counted as 

 one individual unless connections with 

 other shoots could be trr.ced. 



