Management of soil thresholds for seedling emergence to re-establish plant species on bare flats in coastal salt marshes

Abstract

In attempts to mitigate habitat degradation, coastal restoration practices have increasingly been developed. Many restoration practices, such as the introduction of freshwater or seawater, depend on improving the physical conditions in the degraded coastal salt marshes. The effectiveness of restoration practice is the most important focus of coastal wetland managers and ecologists. Here, we explored the effectiveness of irrigation with either freshwater or seawater in achieving re-vegetation on degraded bare flats in the Yellow River Delta through a controlled field experiment and greenhouse experiments. Our results showed that the re-establishment of plant seedlings could occur on bare flats when the two essential thresholds are exceeded. Seawater irrigation was less effective than freshwater because of the failure of the former to meet the salinity threshold for seed germination. It was harder to re-establish seedlings on the bare flats in the supratidal uplands, compared to bare flats in the middle and high marsh, because of the initial high soil salinity and low moisture content, which exceeded the tolerance thresholds of the seeds of several salt marsh species. Information on soil factor thresholds can predict the effectiveness of restoration efforts, an achievement which is instructive for future restoration efforts on bare flats.