Print PageRestoring abandoned agricultural lands provides opportunities for conserving declining habitats. Land use legacies, however, including high soil fertility and pH from agricultural amendments, often persist and promote nonnative species invasions while limiting native species which are competitively inferior under such conditions. Understanding how native species compete with established nonnative species in a restoration context provides important insights into the controls of native species establishment on modified lands. We conducted a field experiment on a former pasture dominated by nonnative plants on Martha’s Vineyard, MA to determine how manipulating soil chemical properties affects competitive interactions between native species that are targets for sandplain grassland restoration and the existing nonnative species. We seeded three native species (Asclepias tuberosa, Schizachyrium scoparium, and Solidago puberula) into ten treatments including three levels of carbon addition to reduce fertility, three levels of sulfur addition to reduce pH, three levels of N addition to understand how elevated N effects competitive interactions, and an unmanipulated control. Native species were grown in plots with existing vegetation and in plots where all nonnative vegetation was clipped. We monitored germination and seedling establishment for two years, and harvested biomass of natives and nonnatives at the end of the second growing season.
Results/Conclusions
Removal of nonnative competitors in the clipping treatment significantly increased the germination of Schizachyrium scoparium but not Solidago puberula or Asclepias tuberosa. Biomass of all species was significantly higher in the clipped plots than in plots with the nonnative vegetation left intact, indicating that competition indeed suppresses native seedling establishment and growth. Addition of sulfur at the highest level (0.27kg m-1) significantly increased biomass and number of seedlings for S. scoparium and S. puberula, but not for A. tuberosa. Addition of carbon also increased germination and biomass of all native target species, however not significantly, suggesting that decreasing soil pH provides natives with a competitive advantage more so than decreasing soil fertility. Biomass of all native species was reduced in the N addition treatments, but not significantly. Our results suggest that decreasing soil fertility and pH benefits native species establishment on modified lands, but physically reducing the nonnative competition is more important for reestablishing native species on invaded, abandoned agricultural lands. Additionally, these results indicate that abiotic treatments may benefit some target species more than others, implying that restoration practitioners must chose treatments based on target species habitat requirements.
