Restoration in New Zealand biodiversity sanctuaries: Effects on community structure from removal of a guild of invasive species

An increasingly popular paradigm for restoration in New Zealand is the establishment of intensively managed conservation initiatives (‘biodiversity sanctuaries’) which seek to eradicate (or reduce to near-zero densities) all invasive mammals present, prevent reinvasions, and restock indigenous ecosystems with formerly present species. Improved pest eradication and detection methods and novel conservation tools such as ‘pest-proof’ fences are supporting this movement. This paradigm is largely based on the assumption that release from these invasive mammals will lead to ecosystem changes that will enhance indigenous biodiversity and meet restoration goals. These initiatives therefore represent a large-scale experiment in ecosystem intervention. We are collating existing data and undertaking new research to determine the preliminary ecosystem changes that do occur, the consequences of these changes, and whether they meet stated restoration goals. Most of these initiatives utilise areas of temperate rainforest. Vegetation changes observed within ten years of release include increased canopy and understorey cover abundance, seedling and sapling densities, and structural complexity; with probable changes to tree regeneration processes. Bird communities have increased in total abundance, but have also resorted so that a group of endemic forest birds are increasing whereas some indigenous and exotic birds of more open habitats are decreasing. Invertebrate communities are also changing in composition and increasing in mean body-size, though not always in diversity or abundance. Changes observed to date include several unexpected results though still within the range of broad restoration goals. These manipulations provide new opportunities for understanding factors determining community composition and ecosystem structure.