Long-lived seed banks of Ammophila arenaria prolong dune restoration programs

Abstract

Marram grass (Ammophila arenaria L. Link (marram grass; Poaceae) has been identified as a major threat to the biodiversity of temperate dune systems outside its natural range. Coastal management and conservation agencies in a number of countries have invested in dune restoration programs involving the removal of invasive species, including marram grass. We investigate the age, viability and the depth distribution of buried seeds of this dune grass within two foredunes in southern New Zealand. The germinability of seeds of known age was determined at St Kilda Beach, Dunedin, New Zealand, to derive a minimum age for the seedbank. Seed was extracted by coring through a foredune to layers of sand of known age based on a time series of foredune-beach profiles. The potential of marram grass to develop large seedbanks in ideal conditions of vigorous plant growth and rapid foredune accretion, was investigated at Mason Bay. Buried seed was extracted using hand-corers to a maximum depth of 4.01 m and tested for germinability. A high proportion of excavated A. arenaria seeds were viable at both sites, including seeds recovered from 4 m depth at St Kilda, estimated to be at least 21 years old. We found no trend of declining viability with increasing depth at Mason Bay, suggesting seed may remain viable for longer than 21 years. Persistent, long-lived, seed banks of A. arenaria develop in foredunes. Restoration programs aiming to eradicate this species are likely to be prolonged (years to decades) as a result of regeneration from seeds that re-enter the shallow seed bank as dunes erode.