Spatial patterns of seedling establishment have been shown to be greatly affected by microtopographic heterogeneity. Addressing the effect of different microtopographic structures on seedling establishment is critical for understanding the complexity and variation of plant distribution and dynamics in coastal salt marshes. However, it is far from clear how species populations respond to differences in microtopography at different tidal zones. Here, we conducted an extensive survey across tidal zones to identify associations between abundance of the halophyte species Suaeda salsa (L.) Pall. with microtopographic heterogeneity. Furthermore, we manipulated microtopographic structures to produce flat, hollow and hummock surfaces, to explore the mechanism of responses of seedling establishment to microtopography across tidal zones.
Results/Conclusions
Microtopographic differences of only a few centimeters were enough to influence seedling establishment by affecting seed retention and post-retention soil conditions. The hollow surfaces trapped more seeds than did flat or hummock surfaces in high-elevation marsh and supratidal zones. Under frequent inundation by tides in low-elevation marsh, the flat surfaces had the most favorable conditions for seed anchorage. Differences in duration of tidal water retention caused by microtopography resulted in different soil conditions. One explanation for the low seedling emergence in hollows in low- and middle-elevation marsh zones was that the lack of oxygen penetration into the soil in the hollows inhibited survival of seedlings, while hummocks and flat surfaces in supratidal zones was against inundated conditions, increasing the drought and salinity stresses on seed germination. Our results suggested that increased microtopography facilitated halophyte establishment in salt marshes, and that the structure of microtopography most suitable for seedling establishment differed among the various marsh zones. Hollows in high-elevation marsh and supratidal zones, or flat surfaces and hummocks in low- and middle-elevation marsh zones provided better habitats for halophyte seedlings, providing important information with which to design and build microtopography to achieve successful halophyte establishment in plant restoration exercises.