Successful restoration of longleaf pine ecosystems and their associated understory may depend on the control of competing vegetation. On flatwoods sites the need for vegetation control is magnified due to the dense shrub understory that smothers young longleaf pine seedlings and the herbaceous vegetation. Although prescribed fire is an effective restoration tool in many longleaf sites, in flatwoods its shrub control is short lived due to the vigorous sprouting of the shrub vegetation. Intensive mechanical site preparation, while yielding enhanced growth of seedlings, may cause extensive damage to the understory vegetation. In our study, we examined the ettects of over the top application of herbicides following site preparation with chopping and burning. The understory species composition exhibited a change without the influence of herbicide treatments. These changes could be attributed to the seasonal changes in the vegetation and the site preparation activities. However, the herbicide treatments as a whole showed a distinct influence on the overall species composition. The understory species diversity increased across all treatments compared to pre harvest vegetation. Two of the herbicide treatments (imazapyr and sulfometuron) had a significant effect on the species diversity. Imazapyr increased species eveness and richness. In contrast, sulfometuron decreased species dversity while resulting in lowered eveness and richness. Contrary to published research, the site preparation conducted in our study did not significantly affect the foliar cover of wiregrass, a key understory species of longleaf pine ecosystems. The herbicide treatments also had no significant effet on wiregrass. © 2005 Nova Science Publishers, Inc.