August, 1955 



EvERS: Hii.i. Prairies of Illinois 



375 



Hill prairies are absent from the gener- 

 ally northeast-facing slopes of the bluffs 

 on the southwest sides of valleys ; these 

 slopes are covered by forests except where 

 they have been cleared and are now in cul- 

 tivation. 



Altitude. — A relationship apparently 

 exists between height of the bluffs and oc- 

 currence of hill prairies. Alore prairie 

 openings and prairie strips are found on 

 the Mississippi River bluffs in Pike. Cal- 

 houn, Monroe, and Randolph counties 

 where the bluff's are high than on those 

 bluffs just north or south of Quinc\ in 

 Adams County where the bluffs are low. 

 At Clendenny prairie (Calhoun County), 

 the bluff rises 220 feet above the bottom- 

 land ; at Sessions ( Pike County) , 240 feet ; 

 at Fults (Monroe County), 3-W feet; and 

 at Phegley and Sampson ( Randolph 

 County), 310 feet. The bluffs north of 

 Quincy are only slightly more than 100 

 feet and those south of Quincy are but 

 120 feet above the Mississippi River bot- 

 tomland. 



Parallel Tributary \'alleys. — Dur- 

 ing the course of field work, the writer 

 observed an interesting feature of the 

 bluffs. In 34 of the 61 hill prairies vis- 

 ited, tributary- valleys are found approxi- 

 mately parallel to and short distances back 

 of the bluffs, fig. 5. In each of the 34 

 sites, the area bet^veerf the major stream 

 valley and the parallel valley, or valleys, 

 is a narrow ridge that is joined to the up- 

 land beyond by another narrow ridge more 

 or less at right angles to the bluff. Hill 

 prairies grow on the upper slope of the 

 ridge that faces the major stream valley, 

 a slope referred to as the upper bluff slope 

 or the brow slope. Narrow ridges of this 

 t>"pe occur where streams have cut back 

 into the valley wall and where, at ap- 

 proximately right angles to tliem, their 

 tributaries have developed. The tributary 

 valleys, mostly parallel to the bluffs, arc 

 V-shaped and forest covered. 



Environmental Conclusions 



As the climate and soils of Illinois per- 

 mit the growth of both prairie and forest, 

 it can be concluded that certain geomor- 

 phic conditions are accountable for the oc- 

 currence of hill prairies on the upper bluff 



slopes. Location, the place in reference to 

 major >tr\'am valleys, and topography, 

 largely the result of the geomorphic his- 

 tory of the region, exert strong influences, 

 or controls, that are responsible for the 

 presence of hill prairies. The growth of 

 grassland rather than forest on the upper 

 bluff slopes is attributed to priority of oc- 

 cupation by prairie species and to the 

 xeric conditions that are produced by the 

 combination of local exposure to the sun 

 and to the wind (especially to wind mov- 

 ing unimpeded across wide Hoodplainsl, 

 the height of the bluffs above the adjacent 

 bottomlands, the steepness and direction 

 of the upper slopes, and the permeability 

 of the substratum. Thus, the hill prairie 

 community is the result of a complex set 

 of conditions, the effectiveness of which 

 is determined by location and topography. 



\EGETATION OF HILL 

 PRAIRIES 



The typical vegetation of hill prairies 

 is the bunch-grass type. In most places, 

 Andropogon scoparius is the dominant spe- 

 cies. In some places, such bunch grasses 

 as Bouteloua curtipendula, A. gerardi, 

 and Sorghastrum nutans are locally dom- 

 inant. In order to learn about the vege- 

 tation, its density, the ground space it oc- 

 cupies, the foliage area or crown cover, 

 the available space per plant, and the fre- 

 quency of occurrence of species in plots of 

 several sizes, the writer made detailed 

 studies of hill prairie vegetation by means 

 of plot studies in two prairies. He also 

 made studies of some characteristics of all 

 stands from species lists and field notes. 



Phegley and Sampson Prairies 



From the 61 hill prairies that he vis- 

 ited, the writer chose Phegley and Samp- 

 son hill prairies for the detailed vegeta- 

 tional studies. These areas are on the 

 same bluff ridge. In their surface fea- 

 tures, Phegley and Sampson prairies are 

 typical of hill prairies. There is a rock 

 ledge and cliff at their base. .A stony slope 

 lies above the rock ledge, and loess caps 

 the bluff. Each prairie area possesses 

 spurs and coves. At the time this study 

 was made, prairie covered both the stony 



