Non-native plant species show a legacy of agricultural history in second-growth forests of southeastern Ohio

In second-growth forest the abundance and diversity of non-native plant species often differ considerably with stand age and the history of disturbance. To understand the role of agricultural history in shaping non-native forest floras, we compared successional trajectories between second-growth stands that were formerly cultivated and pastured, two historically common land uses differing in soil disturbance and vegetation structure. Successional change was inferred from a replicated chronosequence consisting of 40 second-growth stands in southeastern Ohio, USA. The non-native flora was described in terms of community composition and individual species abundance and compared across biotic and abiotic gradients. Abundance of non-native species generally declined through the chronosequence in both land-use categories but was significantly greater in formerly cultivated sites. Non-native richness in the oldest post-agricultural sites was significantly greater than in undisturbed forest, implying that the nonnative flora has not stabilized after 80 years. Species dispersing seeds by ingestion were more abundant in formerly pastured sites; clonal species were more common in cultivated stands. Thus, the non-native forest flora shows a long-lived legacy of variation between stands of different agricultural histories. The distribution of non-native species suggests colonization of established forest as well as relictual survival from the open, agricultural stage. Although non-native abundance declines with successional time, a subset of shade tolerant species should be considered a long-term component of the second-growth flora.