386 



Illinois Natural History Survey Bulletin 



Vol. 26, Art. 5 



Tiible 7. — Foliajie area (square inches) for 

 plants in the central milacre of Sampson and 

 of I'hegley hill prairies. 



Table 8. — Foliage area (per cent of total 

 area) for plants in the central milacre of 

 Sampson and of Phegley hill prairies. 



Species or Type of 

 Plant Growth 



/indropogon scopiiriiij. . . . 



.indropogon gerardi 



Boiilelona curlipendula . . . 



All bunch grasses 



Plants other than grasses 

 All plants 



Sampson 

 Prairie 



76.66 

 0.43 

 0.96 



78.05 

 1.47 



79.52 



Phegi.ev 

 Prairie 



31.79 

 00 

 4.54 



36.33 

 3.92 



40.25 



In iiiiici to estimate foliage area of ./. 

 sioptirius in the central milacre of Samp- 

 son, the writer niultipiieil the ground- 

 space value of this grass by 2.7. The 

 same factor was used in order to estimate 

 foliage area for ./. gerardi. For Boute- 

 loua curtipendiila, a factor of 2.06 was 

 used ; this figure was indicated by separa- 

 tion of the sample from Mud Creek prai- 

 rie. The estimated foliage area for all 

 grass species in the central milacre of 

 Sampson was 4,896 square inches, table 

 7. For Solieliiffo rosettes, growing on the 

 surface of the soil, foliage area was as- 

 sumed to be the same as ground space. 

 The lichens, Leiidea, are not included 

 here as their thalli — -simple plant bodies 

 without true roots, stems, or leaves — 

 grow under the foliage cover of other 

 plants and thus do not contribute to fo- 

 liage area. The estimated foliage area of 

 Agave and Opunlia was 10.35 square 

 inches. For the remaining 251 plants, 

 mosth seedlings or small plants, the fo- 

 liage area was estimated at 0.2 square 

 inch per plant. The aggregate foliage 

 area of plants other than grasses was es- 

 timated to be 92 square inches. The total 

 estimated foliage area in the central mil- 

 acre of the Sampson prairie was 4,988 

 square inches or 79.52 per cent of the 

 milacre, tables 7 and S. 



In the Pheglc\ prairie, both in the cen- 

 tral milacre and in the prairie as a whole, 

 Andropogon scoparius showed obvious re- 

 duction of cover, fig. 12, both at ground 

 level and at foliage levels as compared 

 with this species in the unpastured prai- 

 rie. The leaves covered an area larger 

 than the ground space, but not so large as 

 the area covered by the leaves in the 

 Sampson prairie. Foliage area for A. sco- 



pariits in tile central milacre of the Piieg- 

 le\ prairie was estimated at 1.8 times the 

 ground space; this factor multiplied by 

 the ground space gave an aggregate fol- 

 iage area of 1,994 square inches, table 7. 

 For Hiiuteluiia iiirtipendula, the factor 

 2.06 was again used (as in Sampson), 

 which gave for this species in Phegley an 

 estimated foliage area of 285 square 

 inches. Plants of Lcspcdeza stipulacea, 

 witii an estimated foliage area of 1.5 

 square inches per plant, had an estimated 

 aggregate area of 106 square inches. For 

 prostrate rosettes of Solidago, the foliage 

 area was considered to be equivalent to 

 ground space (as in Sampson). For the 

 remaining plants, all small and mostly 

 seedlings, foliage area was estimated at 

 0.2 scjuare inch per plant. Plants other 

 than grasses had an estimated aggregate 

 foliage area of 246 square inches. The 

 total estimated foliage area in the central 

 milacre of the Phegley prairie was 2,525 

 square inches, or 40.25 per cent of the 

 milacre, tables 7 and S. 



Available Space per Plant. — Avail- 

 able space per plant, the inverse of plant 

 density, is another character that, like 

 density, can be useful in descriptions and 

 comparisons of vegetation. It is simply 

 obtained b\ dividing the area of the meas- 

 ured sample by the number of plants in it. 



\'ariables aftecting available space per 

 plant are size of plants, degree of crowd- 

 ing, and percentage of the measured area 

 covered by plants. In those vegetations 

 which show great disparity in sizes of 

 plants of different species, as sagebrush 

 with short-grass, average available space 

 per plant should be separately found for 

 each component or layer. In the Illinois 

 hill prairies studied, individuals of the 



