Historic deforestation and non-native plant invasions determine vegetation trajectories across an oceanic archipelago

Abstract

Questions

Oceanic islands are global hotspots of endemism and evolutionary radiations but many have been severely degraded by human activities and biological invasions. We evaluated the pace and direction of the natural recovery of ecosystems over 77 years across a subtropical oceanic archipelago including islands of various size, elevation, histories of human settlement and deforestation, and invasions by non-native plants and mammals. This information is essential to guide the ecological restoration of the archipelago.

Location

Forest vegetation on nine of the Ogasawara Islands in the northwestern Pacific Ocean.

Methods

We first digitized historical vegetation data of the Ogasawara Islands collected during field surveys in 1935. Then, after checking their species compositions, we integrated past and present plant community types. Finally, we identified the landscape-scale changes in forest vegetation by comparing vegetation maps from 1935, 1979 and 2012.

Results

Over 77 years, the vegetation trajectories of each island varied depending on the introduction of invasive alien species and the remaining proportion of native forest, the latter of which had a strong influence on the recoverability of native forest.

Conclusions

Our results highlight the importance of the history of invasive species introductions and the remaining proportion of native forest—both of which reflect the intensity of anthropogenic disturbance—in determining the degree of human intervention needed for restoration on oceanic islands.