Plant zonation in a brackish tidal marsh: descriptive verification of resource-based competition and community structure

Abstract

This study examined the hypothesis that the zonal patterns of dominant species in brackish tidal marshes may be explained by resource competition for soil nitrogen and light. This hypothesis was tested by analyzing abiotic and biotic field data collected from a brackish tidal marsh located at Brunswick Point, British Columbia. Biotic data revealed that this tidal marsh is dominated by two species that occupy distinct separate zones correlated to marsh elevation. In particular, sites whose elevation was from −0.80 to 0.20 m (geodetic datum) were dominated by Scirpus americanus, while sites with an elevation 0.20 m were dominated by Carex lyngbyei. Analysis of the relationships between measured variables indicated that total species biomass, species height, and total soil nitrogen were all positively correlated to sample site elevation. Further, the availability of light at the soil surface was found to be negatively correlated to plant biomass and site elevation. These results may suggest that S. americanus is dominant in the low marsh because it is a better competitor for soil nitrogen. Carex lyngbyei may be competitively dominant in the high marsh because its greater biomass and height make it a superior competitor for light. Key words: competition, light, nitrogen, tidal marshes, zonation.