A new evidence base to document millennial changes in coastal vegetation

Abstract Anthropogenic activities are causing detrimental changes to coastal plants– namely seagrass, mangrove, and tidal marsh. Looking beyond recent times and to past vegetation dynamics is critical to assess the response and resilience of an environment to change. Here, we develop a novel multi-proxy approach, providing a new evidence base to decipher long-term change in coastal plant communities. Combining targeted environmental DNA analysis with chemical analysis of soils, we reconstructed 4,000 years of change at a temperate wetland and identified an ecosystem shift that occurred between ~ 1000 and 2000 years ago. What was a previous subtidal seagrass system shifted to an intertidal mangrove environment at present. We demonstrate that high-resolution information on millennial changes in coastal vegetation can be attained through these proxies. This approach could be applied to other ecosystems to improve the way we protect, conserve, and restore vegetated ecosystems.