Using soil seed banks to assess the effectiveness of invasive species control on the island of South Georgia

Invasive species pose significant threats to biodiversity, especially on islands. In addition to the eradication of rats and reindeer on South Georgia, an island-wide management program is well underway with the aim of eradicating 33 non-native plant species. Here, the soil seed bank composition was investigated to evaluate the success of that program. Seeds of all native and non-native South Georgia angiosperm species were imaged, and a dichotomous key made to assist in the identification of extracted seed material. Samples were dry sieved and seed material extracted manually and tested for viability using germination, Cut Tests and Tetrazolium Chloride staining. Viable non-native seeds were found at all four of the locations. However, those of a targeted species were only found at one location. A lesser number of native seeds were found at three of the locations and unidentified seeds were found at all locations. The results suggest that non-native species management will need to continue longer than planned as there was a high density of seeds of a species which was expected to be eradicated. Critical next steps will be identification of the yet unidentified germinated seeds; which are currently growing, specifically to determine if more non-native species are represented. Soil from other locations should also be tested.