Competition Overshadows Associational Defenses from Nuphar advena for Zizania aquatica in a Restored Tidal Freshwater Marsh

Herbivory can hinder restoration success by limiting the recovery of plant biodiversity. This study investigates whether plant-plant interactions, such as associational defenses, can increase the survival of a palatable species in restoration contexts where herbivory inhibits recovery. Specifically, we investigate the potential of associational defenses by the perennial Nuphar advena (yellow pond-lily) to influence the growth and survival of Zizania aquatica (annual wild rice) in a freshwater tidal marsh restoration where goose herbivory has limited Z. aquatica recovery. Wild rice was planted within exclosures and unfenced control plots located within patches of N. advena or adjacent mudflat. In an additional treatment to test the negative effects of light competition, we planted Z. aquatica in exclosures located within experimental clearings in N. advena patches. We also surveyed grazing pressure on naturally-occurring Z. aquatica within transects that spanned N. advena patches and adjacent mudflat. Based on observational and experimental results, N. advena provided clear protection from grazing for Z. aquatica. However, there was a cost to Z. aquatica growing in N. advena patches– plantings within N. advena had greater mortality and significantly reduced biomass due to low light availability.