Restoration of a marsh‐upland ecotone specialist: the role of elevation, amendment, and facilitation

Introduction Restoration of ecotone specialists can be challenging, since ecotones are defined by steep environmental and competition gradients. Restoration success is enhanced by understanding the factors that limit the range of ecotone specialists in the transition zone. Methods We examined conditions affecting the restoration success of coastal gumplant, Grindelia stricta , a salt marsh‐upland ecotone specialist in California. We planted transplants in experiments testing the impacts of facilitation, soil amendment, and elevation on Grindelia survival and health. We also surveyed the seaward boundary of Grindelia at a restored versus natural marsh. Results We found that facilitation by Salicornia pacifica greatly improved outplanting success at stressful elevations, but that soil amendment had little impact. Restoration success appeared to be limited by physical stress at lower elevations and competition at higher elevations, as predicted by the stress gradient hypothesis. Our survey revealed that Grindelia's lower limit is close to the king tide line. Conclusions This study provides a model of how restoration science and experiments can enhance the success of species living in ecotones. Results on this ecotone specialist delineate the zone of likely plant success and highlight the potential value of including facilitation to decrease the stressors near the edge of the ecotone.