Plant invasions threaten a critically imperiled inland salt marsh ecosystem

Abstract Inland salt marshes (ISM) form in non-arid regions when mineral soil is infiltrated by salt-saturated groundwater that rises to the surface in natural saltwater springs or seeps. ISMs were historically found across the eastern USA but presently the few remaining intact are critically imperiled natural communities. Due to their highly saline conditions, ISMs support regionally rare halophytic plants, and they are also susceptible to invasion by salt-tolerant invasive plants. This study had two main objectives (1) compare changes to vegetation and sediment between field surveys spanning 40 years in a State of Michigan, USA ISM (Clinton Saltworks), and (2) assess biotic and abiotic environment shifts due to invasion by two aggressive Typha taxa at a second Michigan ISM site (Hubbard Salt Lick). We found that the state-endangered plants, Eleocharis parvula and Schoenoplectus americanus , have been extirpated from the Clinton Saltworks plant community, corresponding with increased dominance by the invasive plant, Phalaris arundinacea and a reduction in salinity. Within the Hubbard Salt Lick site, invasive Typha spp. had homogenized plant community composition and was directly competing with the rare species. However, both protected species were present directly adjacent to the persistent salt seep, despite encroachment by invasive Typha spp. Inland salt marsh floristic composition and vegetative structure is impacted by invasive species encroachment. Our study highlights the importance of management of invasive plants to promote the integrity of ISMs and maintain rare plant populations dependent on this rare community type.