The influence of exotic species' legacies on pathways of restoration

Restoration practice is often predicated on the expectation that treated ecosystems will proceed predictably toward specific targets. However, persistent influences of conditions present before restoration action is initiated can influence the direction of ecosystem development toward one or more alternative pathways. Such “legacies” of land use, exotic species, or other factors must be understood in order to design appropriate management strategies. I investigated how legacies may influence the pathways that restoration follows by surveying sites in a New York pine barren ecosystem that had undergone restoration treatments to remove the nitrogen (N)‐fixing Black locust ( Robinia pseudoacacia ). I compared soil carbon (C) and N dynamics and plant community composition along a 19‐year chronosequence of treated sites to conditions in untreated forest and remnant, high‐quality barren ecosystems. The presence of Black locust increased N availability and N cycling rates, but those effects did not persist after trees were removed. However, soil percent C and N were significantly lower in tree removal sites than in either Black locust forest or remnant barren sites. These differences lessened as sites aged, indicating that the soil‐based legacies are not permanent. Tree removal transformed vegetation structure, and plant functional traits in tree removal sites were similar to those in remnant barrens. However, even up to 19 years after tree removal, key species—namely woody shrubs—were missing from treated sites. Thus, legacies of exotic species and soil disturbances associated with their removal continued to influence the pathways of ecosystem recovery.