AN ABSTRACT OF THE THESIS OF Joshua B. Nickelson, for the Masters of Science degree in Forestry, at Southern Illinois University Carbondale TITLE: EVALUATING THE SUCCESS OF OAK AFFORESTATION ON FORMER AGRICULTURAL FIELDS IN SOUTHERN ILLINOIS Major Professor: Dr. Eric Holzmueller The establishment of oak (Quercus spp.) plantations has increased over the past two to three decades to reduce fragmentation and promote wildlife habitat throughout the Midwestern United States. However, influences such as competing vegetation, previous land cover, plantation size, and site preparation techniques may have varying outcomes on restorative successes. We established 219 plots (.02 ha) in 29 oak plantations located within Crab Orchard National Wildlife Refuge (Williamson County, Illinois) 15-18 years after mechanical planting. Sampling data for all trees over breast height included species, diameter, and lianas existence on the main bole of the tree. Additionally, free-to-grow status was recorded for all oak saplings and estimated cover of the exotic invasive shrub Elaeagnus umbellata and vine Lonicera japonica were documented. Results show significantly higher numbers of total oaks and free-to-grow oaks in plantings previously cropped in clover and soybeans when compared to the fallow sites host to brush species that received treatment (mowing and or herbicidal application). Significantly less oaks in the soybean and clover categories possessed a vine on the main bole of the tree when compared to the treated brush sites. Brush sites showed a significantly less number of total trees compared to clover and soybean covers and a higher percent of autumn olive cover (%) compared to soybeans. No significance was found in the percent of oaks with a vine, the percent of oaks overtopped, E. umbellata density or L. japonica cover (%) across the four previous vegetation categories. One treatment of pre-planting mowing and herbicidal application is not effective on fallow sites that are host to early successional species and money should not be invested on Quercus trees or mowing and herbicidal treatments in these scenarios. The results suggest that it is best to plant Quercus species immediately following clover or soybean harvest on abandoned agricultural lands before early successional species become established.