Ecological Studies in the Lower Illinois River Valley

Abstract

1. Soil types found in Pike and Calhoun counties at the lower end of the Illinois River were correlated as far as possible with the plant communities growing upon them. The soils in the entire area studied have rather a wide variety of texture and type. There was a small range in the hydrogen-ion concentration of the soils. The variation of the pH of the upland soils was from 6 to 6.6; the floodplain soils was from 7 to 7.8. The pH of the talus slope was 8. The narrow range of pH seems to indicate that it is not an important factor in limiting the distribution of species. 2. A transect of the lower valley affords four general divisions: upland, bluff, transition region, and floodplain. Subdivision of these results in ten major plant communities: upland pasture and old fields, upland forest, limestone bluff, hillside-talus slope forest, talus slope-floodplain transition forest, floodplain forest, floodplain prairie, floodplain lakes and sloughs, river bank, and islands. 3. The dominance index, derived from...