Individual study: Strategies to eradicate the invasive plant procumbent pearlwort Sagina procumbens on Gough Island, Tristan da Cunha
Visser P., Louw H. & Cuthbert R.J. (2010) Strategies to eradicate the invasive plant procumbent pearlwort Sagina procumbens on Gough Island, Tristan da Cunha. Conservation Evidence, 7, 116-122
In 1998, procumbent pearlwort Sagina procumbens a non-native and invasive plant was discovered on Gough Island (Tristan da Cunha). Efforts to eradicate this species have been underway since 2000. To date it has been restricted to a small (400 m length; approximately 1.2-1.6 ha area) but complex stretch of coastal cliffs. Measures of seed density, based on germination trials of soil samples collected from Sagina infested areas, indicate that 'standard eradication' methods (digging up individual plants, heat-treating soil and spot-treatment with herbicides) in place over the last 10 years have resulted in a three orders of magnitude reduction in the seed load. However, around 200 seedlings per m² continue to be recorded due to germination from seeds within the soil. In 2008-09 we investigated the effectiveness of three methods designed to eradicate Sagina on Gough: 'standard eradication' based on methods used in previous years (n = 5 plots); monthly 'herbicide treatment' across the whole plot (n = 4 plots); and 'soil stripping' where all plants and soil was removed down to bedrock (n = 2 plots). Sagina plants remained present within the standard eradication plots, with an average of 64 ± 79 (range 6 - 200) plants recorded per plot cleared in 8-months of monitoring. No Sagina plants were found in herbicide treated plots, although this method is unlikely to tackle the problem of dormant seeds remaining within the soil. Soil stripping was effective at removing the seed bank and only five and 33 plants were found over the 8-months monitoring period. We recommend that a combination of monthly herbicide spraying across the whole infested area (to prevent plants maturing and setting seed) and a programme of soil stripping (working from the outer edge of the plants range) to remove the seed bank, be utilised in order to provide a potential method to eradicate Sagi from Gough.