Spartina patens surveys of flowering density at marsh-forest ecotone

<p>Climate change is driving abiotic shifts that can threaten the conservation of foundation species and the habitats they support. Range shifts are one mechanism of escape, but this requires successful colonization of habitats where interspecific interactions may differ from those to which a species has adapted. For plants with multiple reproductive strategies, these range-edge interactions may alter the investment or allocation towards a given reproductive strategy. In this study, we quantify sexual reproduction of the clonal marsh grass <em>Spartina patens </em>across an inland colonization front into maritime forest being driven by sea-level rise. We find that flowering is variable across <em>S. patens </em>meadows, but consistently reduced under low light conditions like those of the forest understory. Observational surveys of <em>S. patens</em> flowering at four sites in the Delmarva Peninsula agreed with the results of two experimental manipulations of light availability (shading experiment in <em>S. patens</em>-dominated marsh and a forest dieback manipulation). These three approaches pinpointed light limitation as a principal control on <em>S. patens</em> flowering capacity, suggesting that light competition with taller upland species can suppress <em>S. patens</em> flowering along its upland migration front. Consequently, all propagation in shaded conditions must occur clonally or via seeds from the marsh, a reproductive restriction that could limit the potential for local adaptation and reduce genetic diversity. Future research is needed to determine if the lack of flowering is the result of a tradeoff between sexual and clonal reproduction or if it results from insufficient photosynthetic products needed to achieve either reproductive method.</p>