The influence of legacy impacted seed banks on vegetation recovery in a post-agricultural fen complex

Abstract

Agricultural legacies shape soil seed banks, which in turn alter subsequent vegetation recovery. However, the role of legacy-impacted seed banks in shaping wetland-vegetation recovery is not well studied, and hydrologic context may alter impacts of seed bank legacies on extant vegetation. Here we compare seed banks and extant vegetation of four plowed fens to an on-site reference fen to determine (i) if plowing legacies have altered seed banks, (ii) if 13-year post-abandonment vegetation differs from the reference fen, and (iii) whether extant vegetation composition is different than that of seed banks in both reference and plowed fens. The relative abundance of key native graminoid and fen specialist species was greatly reduced in plowed-fen seed banks compared to the reference fen, while weedy/invasive species present in the post-agricultural fens’ seed banks were absent from the reference fen. The depletion of normally dominant native graminoids from seed banks was reflected in extant vegetation. However, shallow water tables predicted shifts in extant vegetation from weedy-mesic annuals to areas dominated by either native clonal forbs or Phalaris arundinacea. In general, plowed plant communities had decreases relative abundance of weedy-mesic species and increased relative abundance clonal forbs or clonal-invasive graminoids compared to seed banks. Our results suggest that while depletion of native graminoids from seed banks plays a part in vegetation recovery, the abundance of weedy-mesic species was not reflected in the recovering vegetation in wetter areas.