Restrictions in the sprouting ability of an invasive coastal plant, Ammophila arenaria, from fragmented rhizomes

The dispersal of rhizomes by waves and ocean currents allows invasive coastal plants to spread rapidly over long distances. Long-term management of these species should recognise the potential for regeneration from rhizome fragments and the likelihood of invasion or reinvasion of dunes. Here, we assess the sprouting ability of Ammophila arenaria (marram grass), an invasive weed of temperate dune systems, which spreads by the marine dispersal of rhizomes. Rhizomes were obtained from four sites in southern New Zealand. Comparative growth trials were conducted to compare the sprouting ability of rhizomes originating from different populations, seasonal restrictions in sprouting potential, and the effects of fragment morphology (length and node number) and rhizome type (vertical or horizontal) on sprouting ability. Overall, the sprouting ability of A. arenaria is high, although we found this ability varied between populations, with season, and in relation to fragment length. Rhizomes formed shoots rapidly when fragmented, indicating a weak or limited innate dormancy. Reduced sprouting appears to be due to variation in the growth reserves stored within the rhizomes at the time of fragmentation. Large numbers of viable rhizomes will be dispersed during events that erode foredunes, and all populations of invasive A. arenaria growing within reach of waves should be considered a potential source of propagules, a conclusion that has implications for management agencies seeking to protect or restore apparently isolated dune systems.