Clonal growth and tiller demography of the invader cordgrass Spartina densiflora brongn. At two contrasting habitats in SW European salt marshes

Salt marshes offer a valuable opportunity to study the effects of environment on the clonal growth of species able to live throughout a wide vertical range on the tidal frame. Spartina densiflora is a species native to South America that is invading marshes in SW Europe, NW Africa, and SW North America, where its populations are found from low to high topographic elevations, altering the composition of plant communities. The aim of this study was to increase our knowledge regarding the competitive ability of S. densiflora, analyzing its clonal growth and its ramet demography during 25 months in two expanding populations at a low and a high marsh. Four clonal characteristics were recorded in both populations: (1) dense occupation of available space inside tussocks; (2) lack of a dormant period and high tiller production rates and growth; (3) evidence of physiological integration between ramets; and (4) high rates of sexual reproduction. Furthermore, S. densiflora developed different strategies of clonal growth in contrasting habitats. Tussocks in the low marsh had lower tiller longevity and higher tiller density, natality, and mortality rates, showing faster ramet turnover than in the high marsh. These clonal growth traits would facilitate S. densiflora persistence under the effects of catastrophic events. Spartina densiflora clonal growth traits indicate strong adaptability to different environmental conditions and strong competitive ability, since its tiller dynamics enable it to invade occupied space, and it effectively colonizes new safe-sites by sexual reproduction. These observations help us to understand how this invader has become the most abundant plant in many estuaries of the SW Iberian Peninsula.

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