Enhancement of lateral connectivity promotes the establishment of plants in saltmarshes

Abstract

Several studies have shown that enhancing lateral hydrological connectivity in river systems can increase the exchange of materials and energy, and improves species diversity, which suggests that it might be a useful ecological restoration tool. The variation in elevation gradient across a saltmarsh system is small, which means that lateral hydrological connectivity in saltmarsh systems is often ignored and the ecological effects caused by the variation in lateral hydrological connectivity are seldom studied. Lateral hydrological connectivity presents when a hydrological connection between marsh plain and tidal creek occurs, as a time interval during which tidal flow occurred. This study explored the effects of enhancing lateral hydrological connectivity on the plant life history process using empirical studies. The enhancement of lateral hydrological connectivity on a temporal scale was achieved by placing hollowed microtopographic structures on the marsh. Data obtained through the high-frequency monitoring of tidal levels was used to calculate lateral hydrological connectivity enhancement, and field control experiments were used to determine the effects of lateral connectivity enhancement on seed retention, emergence, and seedling survival at each life stage. The results showed that lateral hydrological connectivity decreased with the increasing distance to sea and the lateral distance to tidal creek. The hollowed microtopographic structures significantly enhanced lateral hydrological connectivity on the marsh, increased soil moisture content, and reduced soil salinity. Furthermore, seed retention time was significantly increased during dispersal stage, and potential seed establishment was improved. During the emergence and growth stages, the enhanced soil moisture and reduced salinity facilitated the emergence and growth of seeds and seedlings. These effects benefit plant re-establishment in bare areas, especially in areas with low lateral hydrological connectivity. This information could be used to improve the restoration or recovery of vegetation on bare or degraded saltmarshes.