Biogeomorphological processes and structures facilitate seedling establishment and distribution of annual plants:...

Biogeomorphological processes and structures (BPS) can affect plant growth and community structure and promote landscape complexity in ecosystems. However, there is a lack of understanding of how BPS facilitates seedling establishment and distribution of annual plants and promotes the success of coastal restoration. We studied the relationships between seedling establishment of a native annual plant species (Suaeda salsa) and BPS resulting from crabs and plants in a middle elevation salt marsh with moderate tides (where inhabited generally high density of plants and crabs) in the Yellow River Delta of China. While there were many crabs but fewer plants in lower elevation areas with more frequent and stronger tides; and in higher elevation areas with weaker tides there were both fewer crabs and plants. Investigations and field manipulation experiments of microtopography, crabs and plants were conducted to determine if and how these BPS influenced seedling establishment and distribution under tidal influence in the middle elevation salt marshes. Results demonstrated that biogeomorphological structures, mainly concave hollows generated by crab burrowing and concave hollows around plant roots and stems under tidal influence, were associated with the trapping of seeds and influenced the establishment and distribution of seedlings. Additionally, upon senescence, maternal plants with unreleased seeds lodged on the ground and influenced seed retention and seedling establishment. The artificial concave hollows that were created experimentally also trapped many seeds and facilitated seedling establishment. Experimental plantings and creation of artificial hollow microtopography attracted crabs that created burrows, resulting in a positive feedback on seedling establishment. We used information obtained from the experimental component of the study to conduct a hollow microtopography manipulation to successfully restore degraded salt marshes. Understanding the associations between seedling establishment and biogeomorphological processes provides important insights for the utilization of natural or human ecosystem engineering to restore coastal vegetation ecosystems.