Seed bank and regeneration ecology of an annual invasive sedge (Scleria lacustris) in Florida wetlands

Our study supports a working hypothesis that the annual flood/dry cycle characterizing Florida’s seasonal wetlands is the primary factor driving the incidence of the invasive annual sedge, Scleria lacustris, by selecting strategies integral to seed bank function and seedling regeneration. Particular strategies of seed bank persistence, seed bank survival, dormancy break and seedling emergence were identified and demonstrated as influenced by the hydrologic regime.;Basic characteristics of the S. lacustris seed bank were evaluated in 2004 at two wetlands in south central Florida where soil was sampled twice yearly (before and after seedling emergence) and seedling emergence was monitored continuously. Seed extraction from the soil samples demonstrated the presence of up to 2,331 seeds m-2 with 88% viability in the top 9 cm of soil before springtime germination. Although seeds were concentrated in the upper 3 cm, seed depletion from germination increased with depth. Regardless of significant levels of seed bank depletion and a resulting seedling monoculture, a viable seed bank at the end of summer was indicative of a functionally persistent seed bank strategy.;Persistence was considered to be a response of the innate dormancy, which was confirmed in 2005. Seed storage studies, conducted from 2004 to 2006 under field and controlled conditions, demonstrated that dormancy was influenced by the hydrologic environment of the seed bank which additionally functioned to affect viability and germination potential. Seed bank persistence served to provide for seedling populations for at least four years under annual, experimental flood/dry cycles. Under continuous inundation, seed bank viability was maintained in a presumably active metabolic state, for at least four years. On the other hand, a dry storage environment maintained viability through dormancy for the short term, but led to sooner and greater mortality rates. Fluctuating and intermediately moist conditions also tended to induce a higher state of physiological activity in the seed bank.;In 2005 and 2006 seed bank evaluation and vegetation monitoring were conducted along three transects of the hydrologic gradient at a single depression marsh. These climactically opposing years supported experimental trials revealing seedling regeneration as restricted to well drained soils following surface water dry down. Furthermore, seedling regeneration, survival and adult productivity were significantly different along the gradient, as indicated by a cut off from the optimum conditions provided by the previously inundated portion of the marsh. The contributing influence of vegetation gaps that developed in the previous inundated regime was significant. Results support acceptance of the working hypotheses by indicating that both seed bank and regeneration strategies are highly promoted/selected for by the hydrologic regime of the seasonal marsh and may explain the invasive colonization and apparent advantages of this annual sedge in seasonal wetlands of Florida.