Earth Fire and Water: applying novel techniques to eradicate the invasive procumbent pearlwort Sagina procumbens, on Gough Island, a World Heritage Site in the South Atlantic

The Eurasian plant procumbent pearlwort (Sagina procumbens) was first reported in 1998 on Gough Island, a cool-temperate island and World Heritage Site in the central South Atlantic. The first population was discovered adjacent to a meteorological station, which is its assumed point of arrival. Despite numerous eradication attempts, the species has spread along a few hundred metres of coastal cliff, but has not as yet been found in the island’s sub-Antarctic-like mountainous interior. At South Africa’s sub-Antarctic Prince Edward Islands Sagina is spreading rapidly in vegetated and unvegetated habitats, and is considered beyond control. A similar situation could eventuate on Gough Island if the plant spreads inland, with deleterious effects on the island’s ecosystems. Eradication methods progressively used on Gough Island included mechanical removal and dumping of plants and seed-infested soil at sea well away from the island, application of herbicides to kill both growing plants and germinating seeds, gas flames to kill seeds and seedlings in rock cracks, near-boiling water to kill seeds in soil, high-pressure water jets to strip infested areas of soil and peat down to bedrock, and spraying with salt water. Germination trials have shown that spraying with sea water inhibits seedling production and a steady decline in seed load in infested areas over almost a decade. However, eradication has been hampered by the plant’s inconspicuous nature, fast growth rate, large seed production leading to an equally large seed bank, long-lived seeds, difficult terrain that requires qualified rope-access technicians to work in safety, and the island’s remote location. Although eradication has not yet been achieved, S. procumbens remains confined to its current restricted distribution on the island.