Biomass and clonal architecture of the cordgrass Spartina patens (Poaceae) as an invasive species in two contrasted coastal habitats on the Atlantic coast of the Iberian Peninsula

Background and aims - The spread of invasive exotic species is one of the most important threats for salt marshes and cordgrasses (genus Spartina) are among the most invasive halophytes. Recent analyses have revealed low levels of genetic diversity within the European cordgrass Spartina patens, clarifying that it was introduced from a narrow genetic pool of plants from North America. As biomass and intratussock structure are key functional traits in the ecological behaviour of cordgrasses, our aim was to document this here for the first time in Spartina patens in Europe. Methods - This work analyses above- and below-ground biomass and intratussock structure for two Spartina patens populations in Southern Spain in the two main invaded habitats in Europe, coastal dunes and brackish marshes. Key results - Spartina patens showed higher above-ground biomass and higher above: below-ground biomass ratio in the brackish marsh than on the coastal dunes due to higher live shoot densities with similar shoot heights. Sexual reproduction of Spartina patens was very limited in both studied populations since only a few inflorescences were recorded in just one tussock in the marsh. Conclusions - Our results for introduced Spartina patens in Spain are compared with those recorded for cohabiting cordgrasses, the native European Spartina maritima and the invasive Spartina densiflora, as well as with Spartina patens in North American marshes. Spartina patens appears as a species with moderate invasive potential in European coastal marshes and dunes since it shows very low sexual reproduction but a high phenotypic plasticity, which would support its invasive capacity. Eradication efforts are most cost effective in the early stage of infestation, when population sizes are still relatively small, and should thus be a focus of the control efforts of S. patens in the Southwest Iberian Peninsula as well as in other European areas, where this cordgrass is still not very abundant.