European buckthorn (Rhamnus cathartica) invades woodlands and forests in the Northeast and upper Midwest of the US. Once established, this large shrub often forms dense thickets and significantly diminishes native plant species diversity. Ecosystems inundated with buckthorn are associated with elevated soil N, altered ecosystem processes (accelerated decomposition and nutrient cycling) and greatly modified soil foodwebs and these effects persist following buckthorn removal. We hypothesize that the legacy effects of buckthorn invasion contribute to its re-invasion and hinder native plant re-establishment after buckthorn removal. Furthermore, we hypothesize that successful prevention of buckthorn re-invasion and restoration of native plant communities will be promoted by reducing buckthorn’s legacy effect of elevated soil N by employing management techniques that reduce soil N concentrations after buckthorn removal. The following treatments are examined in a randomized block design experiment conducted in a heavy invaded old-field site in Mettawa, Illinois: cutting and removal of R. cathartica followed by native or cover crop seeding; cutting and removal of R. cathartica followed by tilling mulched R. cathartica wood or commercially available wood followed by native or cover crop seeding; and cutting and removal of R. cathartica followed by planting two rotations of corn.  

Results/Conclusions

Our results indicate that reinvasion by R. cathartica was significantly reduced when woody mulch (using mulch composed of R. cathartica wood, or a commercially available mulch) was incorporated into the soil. Mulch incorporation also resulted in higher decomposition rates, higher earthworm populations and lower primary productivity of the first year vegetation. The 2 year corn rotation resulted in a reduction of total soil N, but no significant reduction in soil inorganic N (NH₄⁺ + NO₃^-). Bioavailable plant nutrient supply rates, measured using PRS™-probes were altered in all restoration treatments. Plant diversity was not significantly different in any of the restoration treatments. We will be able to report on results from the second spring season of this experiment. This work is discussed in the context of more general efforts to incorporate soil ecological knowledge into restoration practice.