European buckthorn ( Rhamnus cathartica), a prevalent invasive shrub in relict woodlands throughout Northeastern Illinois, alters certain soil properties in a manner that may have importance for the long-term conservation management of these systems. We found that soil in areas of the woodland where buckthorn dominates have higher percentage of nitrogen (N) and carbon (C), modified nitrogen mineralization rates, elevated pH, and higher soil moisture than those areas where buckthorn was not present. Although there were small C:N ratio differences at two of the three sites, there was no overall difference in C:N ratios between the sites. Since the long-term management for these systems often calls for restoration to pre-invaded conditions, the likelihood that the invasive shrub is creating a legacy effect of altered ecosystems properties may call for reassessed management strategies.