Spartina patens surveys of flowering density at marsh-forest ecotone

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 Spartina
patens across an inland colonization front into maritime forest being
driven by sea-level rise. We find that flowering is variable across S.
patens meadows, but consistently reduced under low light conditions like
those of the forest understory. Observational surveys of S. patens
flowering at four sites in the Delmarva Peninsula agreed with the results
of two experimental manipulations of light availability (shading
experiment in S. patens-dominated marsh and a forest dieback
manipulation). These three approaches pinpointed light limitation as a
principal control on S. patens flowering capacity, suggesting that light
competition with taller upland species can suppress S. patens 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.