FOREST COMMUNITIES OF A HYDROLOGICALLY MODIFIED FLOODPLAIN ALONG THE LOWER 
KASKASKIA RIVER.

Susan P. Romano1,2 , James J. Zaczek1, Sara G. Baer1, and Karl W. J. Williard1.
1Department of Forestry, Southern Illinois University, Carbondale, IL  62901-
4411, 2Department of Plant Biology, Southern Illinois University, Carbondale, IL  
62901-6509.

Alterations of floodplain hydrology in the lower reaches of the Kaskaskia River 
have caused concern among landowners and resource managers for the health of the 
associated riparian forest communities.  A dam was completed upstream in 1967 at 
Carlyle, Illinois on the Kaskaskia River to control flooding and improve 
downstream navigation.  This study was initiated to determine if there is a 
relationship of forest tree composition and growth to the altered flooding 
regime. Three study sites were chosen, Posey, Venedy, and Fayetteville, with 
distance from the dam and proximity to river gauging stations as selection 
criteria. Overstory and midstory strata were sampled with circular plots, 0.04 
hectares and 0.0025 ha plots, respectively. The Posey site is located 6.4 km 
below the dam.  Forest overstory stratum at this site was primarily composed of 
high densities of Acer saccharinum, Celtis occidentalis, and Fraxinus 
pennsylvanica.  More Ulmus americana is found in the overstory at this site than 
at the two sites downstream.  Very little Quercus bicolor and only scattered 
Quercus palustris were present in the overstory.  Midstory species were 
predominately C. occidentalis, U. americana, Acer negundo, and A. saccharinum.  
Some scattered Q. palustris were also in the midstory.  The floodplain forest at 
this site had few Quercus sp. in the overstory and midstory forest strata. 
Venedy is 32 km below the Carlyle dam. The Venedy floodplain overstory stratum 
was composed mostly of C. occidentalis, U. americana, A. saccharinum, and A. 
negundo.  The Quercus overstory component was sparse at this site, with several 
canopy Quercus scattered in throughout the floodplain area.  There were very few 
Quercus in the midstory; none were present in our midstory plot sampling.  
Midstory forest species at Venedy included C. occidentalis, U. americana, A. 
negundo and Carya ovata.  There was less A. saccharinum in the midstory at this 
site than at the Posey and Fayetteville sites. The Fayetteville site is 56 km 
below the dam. The Fayetteville overstory stratum was mostly A. saccharinum, C. 
occidentalis, and F.  pennsylvanica. Midstory regeneration was primarily U. 
Americana, C. occidentalis, F. pennsylvanica, A. saccharinum, and A. negundo.  
Quercus bicolor and Q. palustris were present in the midstory, unlike the other 
sites.  Relationships of species composition and site factors of soil texture, 
elevation, and flood inundation period will be determined with further data 
collection and analyses. Upon completion, this research will provide insight 
into floodplain forest communities and recommendations for better management and 
understanding of these areas. 

Keywords: floodplain, Kaskaskia River, forest, riparian, hydrology