Abstract
Liberty Island, California, is a historical freshwater tidal wetland that was converted to agricultural fields in the early 1900s. Liberty Island functioned as farmland until an accidental levee break flooded the area in 1997, inadvertently restoring tidal marsh hydrology. Since then, wetland vegetation has naturally recolonized part of the site. We conducted a seed bank assay at the site and found that despite a lack of germination or seedling recruitment at the site, the seed bank contained a diverse plant community, indicating that the site’s continuous flooding was likely suppressing germination. Additionally, the frequency of germinating seeds in the seed bank did not represent the dominant adult plant community. We conducted a cold stratification study to determine if this observed disparity could be explained by seed germination dynamics, and whether germination could be enhanced using a pre-germination cold exposure, particularly for species of concern for wetland restoration. The cold stratification study showed that longer durations of pre-germination cold enhanced germination in Schoenoplectus acutus, but reduced germination in Schoenoplectus californicus, and had no effect on Typha latifolia. Overall, germination of S. californicus and S. acutus was much lower than T. latifolia. Our findings suggest that seeding may not be an effective restoration technique for Schoenoplectus spp., and, to improve restoration techniques, further study is needed to more comprehensively understand the reproduction ecology of important marsh species.
Highlights
Worldwide, tidal freshwater wetlands have been in decline as a result of human alteration of natural hydrological regimes (Zonneveld 1960; Dahl 1990; Kotze et al 1995; An et al 2007; Barendregt et al 2008; Davidson 2014)
Flooding Study Experimental Design We investigated the effect of flooding on seed germination in three species (S. acutus, S. californicus, and Typha latifolia), using four pre-germination cold stratification duration treatments; two flooding depths (10 cm and 30 cm); and four replicates of each
Seed Bank Assay A total of nine species emerged from the seed bank: Alopecurus carolinianus, Cyperus eragrostis, Gratiola ebracteata, Lamium amplexicaule, Melilotus alba, Poa annua, Schoenoplectus californicus, Typha sp., and an unidentifiable dicot, which died before we could identify it
Summary
Tidal freshwater wetlands have been in decline as a result of human alteration of natural hydrological regimes (Zonneveld 1960; Dahl 1990; Kotze et al 1995; An et al 2007; Barendregt et al 2008; Davidson 2014). Efficient restoration of these degraded wetlands and creation of new wetlands habitats is desired globally to restore the important ecosystem functions these systems. Knowledge gaps still exist in basic plant ecology, which will be crucial to address, to ensure successful science-based ecosystem restoration, in wetlands
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