We are currently investigating seed dispersal dynamics of a brackish tidal marsh in Solano County, California. Through the evaluation of seed bank surveys, seed traps, and flotation experiments, we seek to understand dispersal syndromes of tidal marsh plants, and how dispersal relates to key processes that shape vegetation patterns in tidal wetlands. In particular, we are interested in whether seed dispersal results in localized seed input, or if the seeds are well-distributed. Further, if the seeds are well-distributed, do the physical gradients of the marsh determine the distribution of species?
Previous studies have demonstrated that vegetation patterns in tidal wetlands tend to be driven by inter-specific competition as well as tolerance to salinity and inundation, despite ubiquitous dispersal of propagules by taxa established throughout the greater estuarine wetlands of the region. If hydrochory is the principal mode of dispersal, we predict that all areas of the marsh will have representative species from other zones, which the seed banks should directly reflect. Despite widespread dispersal, above ground vegetation in tidal marshes tends to adhere to strict zonation patterns. We predict that the results of these experiments should help demonstrate that different zones are assembled by physical processes, independent of the composition and richness of the seed bank flora.
Positioned at the confluence of San Francisco Bay and the Sacramento-San Joaquin River Delta, the Suisun March hosts an impressive diversity of native California flora, including the federally endangered Suisun Thistle (Cirsium hydrophilum var. hydrophilum). The results of our studies will help inform future management and restoration efforts for the Suisun Thistle, as well as the greater estuarine complex, in the face of myriad effects associated with global climate change and sea level rise.
Results/Conclusions
Preliminary results have shown that the seeds of Suisun Thistle remain floating for upwards of 25 days, indicating that hydrochory is a likely mode of dispersal. Seeds from other taxa sampled floated for durations considerable enough to indicate hydrochory as a likely dispersal mechanism (10-60 days).
In both the seed bank and seed trap germination experiments, virtually all taxa appear to be well-distributed throughout the different zones of the marsh. Richness has been fairly high across all samples, ranging from 5-18 taxa per soil core. Certain taxa are extremely well represented in the seed bank (Juncus balticus, Epilobium ciliatum, Lepidium latifolium), while the Suisun Thistle is poorly represented, indicating that seed production is one likely constraint.