RADIAL GROWTH RELATIONSHIPS OF QUERCUS SPP.  AND FRAXINUS 
PENNSYLVANICA TO FLOODING IN THE LOWER KASKASKIA RIVER, 
SOUTHERN ILLINOIS, USA

Susan P. Romano12, James J. Zaczek1, David J. Gibson3, Sara G. Baer3, and Karl W. J. 
Williard1
1Department of Forestry, Southern Illinois University-Carbondale, Carbondale, IL  
62901.  2Department of Biological Sciences, Western Illinois University, Macomb, 
Illinois  61455.  3Department of Plant Biology, Southern Illinois University-Carbondale, 
Carbondale, IL  62901
	Dams, canalization, and levee installation often alter flooding conditions within 
the floodplain of large river systems.  The radial growth of floodplain forest trees may be 
affected by these changes.  Previous research has indicated that various flooding 
conditions can have no effect, a negative effect, or a positive effect on radial growth of 
Fraxinus pennsylvanica and Quercus spp.  Growing season flood frequency and duration 
were modeled for three sites along the Lower Kaskaskia River with historic river gage 
data, on-site monitoring wells, GPS, and ArcMap.  Step-wise multiple regression was 
used to determine relationships of standard ARSTAN chronology output (radial growth) 
and mean annual growing season flood variables before and after the installation of the 
Kaskaskia  River dam including:  number of days of flooding, number of days of flooding 
lagged 1 year, flood frequency, flood frequency lagged 1 year, duration of flood event, 
duration of flood event lagged 1 year, average frequency/total days of flooding, average 
frequency/total days of flooding lagged 1 year, Palmer Drought Severity Index during  
the growing season, (PDSIGS) and PDSIGS lagged 1 year.    
	The PDSIGS which utilizes rainfall and temperatures to estimate regional high or 
low moisture stress tended to be related to either F. pennsylvanica and Quercus spp. or 
both species radial growth at most sites for the corresponding year or sometimes for the 
following year’s radial growth during the time period before the dam.  The weather prior 
to dam construction was more variable than after the dam construction, with a major 
flood period followed by a drought period prior to the dam.  After the dam, PDSIGS was 
related to radial growth only for Fraxinus at one site.  The flood frequency, total number 
of flooded days, the length of flooding events, and flood frequency/total number of 
flooded days, were all related to radial growth, depending on the site and species.  
Flooding was more frequent, with shorter flood events, and for a greater number of days 
during the growing season at Posey before dam installation.  Hydrology at Venedy before 
the dam was similar to hydrology following dam construction.  This was primarily due to 
tributary inputs above the site.  At Fayetteville, the length of flooding events was 
significantly shorter than at Posey, due to the canalization of the River just below the site.  
      This study indicates that the collective influence of important flood and weather 
relationships contribute to the complexity of the positive and negative impacts of these 
factors on radial growth.  Factors may need to reach a threshold point or value before 
they exert a significant influence either positively or negatively on growth, or when the 
factor surpasses a threshold it can mask the effect that other variables have.  
Relationships of flood length, frequency, and weather factors to radial growth will shift 
as any one factor may become the dominant influence for a particular year. 

Keywords:  radial growth, flood frequency, flood duration, Fraxinus pennsylvanica, 
Quercus spp.