Volunteers were used to map invasive plants in 25 ha of one of the best remnants of Scalesia pedunculata forest at Los Gemelos, Santa Cruz Island, Galapagos. The most dominant invaders were the trees Cestrum auriculatum, Cedrela odorata and Cinchona pubescens, a vine Passiflora edulis, and the shrub Rubus niveus. Forest structure at the site suggests that further cyclical stand-level dieback, reportedly characteristic of S. pedunculata forests, is unlikely to occur in the near future. Although the invasion at Los Gemelos is continuous, we conclude that dieback provides extra opportunity for the establishment of invasive plants. Management is required to reduce invasive species impacts on the forest.