Examining the impact of control over time on the seed bank of Mimosa pigra on Top End, Australia floodplains

Mimosa, Mimosa pigra L., is renowned for producing an abundance of seeds, many of which remain in the population as a persistent seed bank. Integrated control programs have been effective in reducing the above-ground cover of mimosa but little is known about its effect on the soil seed-bank. The viability of mimosa soil seed banks following integrated control was investigated in two floodplains in the Top End of northern Australia in relation to time since control and vegetation type. Mimosa seed banks under all vegetation types were considerably lower (by at least 50%) than under stands of mimosa. Most of this reduction occurred within the first year of control, although seed stores still remained in the soil three years after initial control. There were few consistent differences in the density of mimosa seed banks between vegetation types. The results also indicated considerably lower seed counts under mimosa compared to previous studies. The lower seed count under mimosa may be attributed to the effectiveness of current biological-control programs. Integrated control therefore appears to be reducing viable mimosa seed. Nevertheless, significant numbers of seeds remain in the seed bank, highlighting the importance of follow-up control and sound land-management practices (avoiding overgrazing and maintaining suitable vegetation cover) in order for competitive species to suppress mimosa re-establishment.