Rewilding giant tortoises engineers plant communities at local to landscape scales

Trophic rewilding is increasingly being used to promote megafauna reintroductions to island ecosystems, yet ecosystem response to population restoration once megafauna reintroduction occurs remains understudied. In this study of a population of Galapagos giant tortoises reintroduced to an arid island, tortoise exclosures monitored over an 8-year-long period revealed that, in response to the presence of tortoises, herbaceous plant cover and numbers of regenerating woody plants decreased, whereas extent of grass cover increased. Vegetation mapping over a 15-year-long period across the island indicated a threshold density of 1–2 tortoises per hectare halted incursion of woody plants and triggered a shift in this savannah-type ecosystem toward more grasses. Restoration of this giant tortoise population has shaped plant communities at both local and landscape scales with cascading effects on many components of biodiversity on the island.