Invasive populations of Paraserianthes lophantha in Auckland, New Zealand: distribution, seed bank and methods for control

Abstract

Paraserianthes lophantha is a South Western Australian species that has been become invasive outside of the native range. Despite a widespread distribution, there is little literature available on this species. This study therefore aimed to add to the collective knowledge of P. lophantha and attempted to provide options for control and management. Examination of the Auckland distribution showed that P. lophantha is spread across the wider region. The locations highlighted the tolerance of this species for disturbed environments, with particularly high densities found on transport corridors. This relationship was further explored in the Franklin District, where two sub populations were visible, suggesting two possible introduction points. There were no significant relationships between site characteristics and stem density in road verge populations, once again highlighting the broad tolerance range of P. lophantha. Analyses of the community composition under stands of P. lophantha showed a number of native, introduced and weed species. Overall, sites were able to be grouped according to the levels of presumed disturbance, with sites with less current disturbance featuring a higher number of native species. The ability of P. lophantha to act as a nursery crop for native species could be neither discounted nor endorsed. The seed bank of P. lophantha was found to be primarily contained within a distance of 1m from the dripline and between 0-5cm from the soil surface. Sampling of the buried seed over a presumed chronosequence showed a rapid accumulation of seeds over time, with seeds ranging from 500 seeds m-2 at the youngest site to 1100 seeds m-2 in the oldest site. A significant difference in the soil seed bank densities and seed viability was found between a revegetated quarry site (Waitakere) and a weedy quarry site (Mount Wellington). Further studies would be warranted to explore the reasons behind these differences. Paraserianthes lophantha is known to exhibit coat imposed dormancy which can be broken through exposure to high temperatures. The ability to break dormancy of buried seed was tested in both lab and field settings to varying success. Exposure to 80⁰C dry heat in lab settings stimulated germination to 68%, a level comparable to that of viability tests. Results of solarisation in field experiments showed that further trials would need to be undertaken before this method is able to be translated to the field. Overall, this study was able to highlight the invasive potential of P. lophantha and further research would be necessary to accurately assess the level of management required and further refine management techniques.