Early responses of regeneration to weeding and herbicide application to control Guinea-grass in a 20-year-old Atlantic Forest undergoing restoration

Among the invasive grasses harming natural ecosystems in Brazil, Guinea-grass (Megathyrsus maximus) has received significant attention due to its high invasive potential and damage it causes to restoration sites. Here, we show the response of seedlings (10 cm to 1 m) and saplings (>1 m) one year after Guinea-grass removal in a 20-year-old restoration site in the Atlantic Forest. Thirty 10 x 20 m plots were installed and assigned into three treatments: control, mechanical removal using gas-trimmers, and mechanical removal followed by the application of Roundup Transorb R (glyphosate). Forest canopy and grass cover were also assessed. Guinea-grass was negatively correlated with woody species richness and abundance. Forest canopy cover was positively related to species richness and abundance, and negatively related to Guinea-grass. Treatments applied were successful in controlling the plant invader and did not cause any significant reduction in the total abundance or richness of saplings after one year. For seedlings, however, the abundance and richness of pioneer woody species increased over time with mechanical removal, while the abundance and richness of non-pioneer woody species decreased in plots treated with herbicide. We expect regeneration responses to continue to improve with time. Our results support the use of both herbicide and mechanical removal to reduce Guinea-grass in Atlantic Forest sites undergoing restoration, although the use of herbicide lowers native seedling richness in the short-term, while mechanical removal may be better for small sites, where it is more feasible and less demanding.