Competitive reversal between plant species is driven by species-specific tolerance to flooding stress and nutrient acquisition during early marsh succession.
Understanding plant species interactions along successional trajectories is critical for managing and restoring ecosystems, as both resource availability and abiotic stresses change over time to affect competitive outcomes and species distributions. Newly created ecosystems experience a succession of plant species and rapid changes in resource availability, which may influence the outcome of biotic interactions. How these biotic interactions vary along abiotic gradients in early successional systems is not well understood. Here, we tested the hypothesis that species-specific tolerances to flooding would influence their relative ability to capture resources (i.e. nutrients) and affect competition intensity between pioneer and secondary successional species in an early successional created tidal marsh. We transplanted a competitively dominant higher marsh species, saltmeadow cordgrass (Spartina patens), across an elevation gradient within and outside of clones of a pioneer stress-tolerant low marsh species, smooth cordgrass (S. alterniflora). Within 6 months, S. alterniflora had suppressed the stature and growth of S. patens; however, the magnitude of this competitive effect increased at lower marsh elevations where S. alterniflora was more efficient at capturing available nitrogen (N). In unvegetated areas, where S. patens vigour was high, the amount of available N was approximately 40 times greater than within S. alterniflora clones. Synthesis and applications: Our results demonstrate that competition intensity of the stress-tolerant species over the competitive species depended on relative resource capture in response to abiotic stress. Managing for specific vegetation communities in marsh restoration, therefore, requires insight into these relationships and interactions. Specifically, marsh restoration in high nutrient environments will limit the succession to high density competitive species due to competition with stress-tolerant pioneer species, particularly at lower elevations.