Disperser communities and legacies of goat grazing determine forest succession on the remote Three Kings Islands, New Zealand

Abstract

Many remote islands are degraded as a result of deforestation and browsing of vegetation by introduced goats. Goat eradication is therefore a focus for island restoration, but there are few long-term records of change on islands after eradications. In 1946, three permanent plots were established immediately after goats were eradicated from Great Island (Manawa Tawhi), 60 km from northern New Zealand, and provide a 57-year record of change across a sequence of forest succession. Since 1946, the native and non-native bird communities that disperse 75% of the woody flora have increased from six to eight species and bird-dispersed woody plants in plots have increased from 7 to 11 species. After 1946, palatable trees were recruited in the plots. Unpalatable understorey sedges, present when goats were abundant, have persisted and may impede tree seedling establishment. Of the bird-dispersed woody plant species, 41% occur in the plots compared with 67% of the non-bird-dispersed species. Large-seeded species were unable to germinate away from parents until native pigeons Hemiphaga novaeseelandiae were present during the last decade. Forest succession is a consequence of interactions between the legacy of goat grazing and current disperser communities. Survival of seed-limited rare plants is not guaranteed in these circumstances. Although non-native goats no longer influence succession directly, non-native birds have been and remain important components of the disperser community. Our study supports the view that a whole-ecosystem understanding of the interactions between native and non-native species is needed to predict the consequences of eradications on islands worldwide.