Experimental removal of an invasive tree in Galápagos promotes native and endemic species but also secondary invaders

Plant invasions can form unique plant communities that are sometimes thought to be so different from native-dominated communities that restoration is either not possible or not logistically feasible. However, few invader removal studies have been conducted in these “novel” ecosystems on islands. To test the potential for restoration of a highly invaded ecosystem in Galápagos, we mechanically removed the canopy-dominant tree (Cedrela odorata) from 48 replicate plots (of 4 m × 4 m each and spread in three separated sites) and evaluated responses of seeds and seedlings, including germination, establishment, and growth, of eight total endemic, native, and invasive plant species compared to control plots where C. odorata was not removed. Invasive tree removal resulted in approximately 30% greater canopy openness compared to control plots, but did not affect the emergence of any species. However, invader removal significantly promoted seedling establishment and growth of the threatened endemic tree Scalesia pedunculata that historically occupied the site. Around 40% of S. pedunculata individuals established under the invader removal treatment while only 5% established in intact control plots. Moreover, S. pedunculata growth was, on average, 65% greater in plots where the invader was removed. Recruitment of S. pedunculata was inhibited by seedling predators (particularly invasive rats) and coverage by fast-growing secondary invaders that also benefited from C. odorata removal. Resolving both native and invasive plant species responses to invasive species removal is an important step in understanding and predicting ecosystem dynamics that determine whether restoration goals in “novel” ecosystems are achievable.