Carpobrotus Management in a Mediterranean Sand Dune Ecosystem: Minimum Effective Glyphosate Dose and an Evaluation of Tarping

At a global scale, biological invasions represent one of the most important threats to biodiversity conservation. The Carpobrotus (Aizoaceae) genus, which is native to South Africa, has been introduced into five different continents and is particularly invasive in many coastal habitats. The application of glyphosate avoids some problems associated with manually controlling Carpobrotus over large spatial scales. However, before this practice can be extended and its impact minimized, its effectiveness under different application conditions must be assessed first. Thus, glyphosate was sprayed at different concentrations (0.5, 0.4, 0.3, 0.2, 0.1, and 0.05 g/m2) on experimental plots with 100% Carpobrotus coverage to determine the minimum effective dose. Tarping was also evaluated as an alternative method for Carpobrotus management over reduced areas. Thus, four different weed-control fabric types were tested: black anti-weed fabric, sewn felt, black G-300 polyethylene, and Fijavert coconut-anti-weed matting on experimental plots with 100% Carpobrotus coverage. The obtained results showed that the minimum effective dose of glyphosate which prevents Carpobrotus regrowth in dune ecosystems was 0.4 g/m2. It was also shown that at least three months of tarping were required under winter conditions to produce complete Carpobrotus plant wilting and thus, prevent their regrowth. No significant effect on Carpobrotus growth was observed in terms of the fabric type used for the tarping tests. The presence of native species seedlings in the experimental plots after the death of the Carpobrotus plants following the application of herbicides or tarping was also monitored.