Ecological restoration at Mainland Islands in New Zealand

Abstract

While important advances have been made in recovering threatened species and restoring damaged habitats on offshore islands, effective conservation management is also required on the main (North and South) islands if representative elements of New Zealand's remaining biodiversity are to be protected. The recent initiation of Mainland Island projects constitutes an important step in that ecosystem-focused restoration goals are being pursued at mainland sites. The intensity and scope of pest control undertaken at Mainland Islands is greater than has normally been the case previously, as has been monitoring of results and conservation outcomes. Preliminary results suggest that declines in monitored species have been arrested and ecological processes re-vitalised. In addition to restoring values at individual sites Mainland Islands may be important places where our capacity to manage ecosystems more generally may be developed. Advances in our understanding of ecological processes and of responses to management using sound scientific procedures as part of operational programmes could lead to improved predictions to underpin management decisions. Refinements to management techniques and the development of appropriate skills, as well as enhancing public support and involvement could also be expected to have major benefits for conservation management more widely.

Introduction

Like many island archipelagos New Zealand's biota has changed dramatically as a result of human colonisation. Many species have gone extinct and a relatively large proportion of those remaining are threatened with extinction. The main agents of decline have been habitat loss and fragmentation and the on-going impacts of introduced pests.

New Zealand conservation practitioners have achieved some remarkable successes in averting further extinctions and rehabilitating habitats on offshore islands. Vulnerable species have been translocated to predator-free islands in order to establish new populations. A growing array of introduced pests (particularly mammals) have been eradicated from islands up to 2000 ha in size, creating opportunities for species recovery and ecological restoration.

While this focus on offshore islands will continue, it is clear that it will not be possible to sustain all or even the majority of New Zealand's remaining indigenous biodiversity on offshore islands alone. There is a need to also achieve important conservation outcomes at mainland sites.

Six ‘Mainland Island’ projects were initiated by the New Zealand Department of Conservation in 1995 and 1996. Their key features are that they have ecosystem-focused restoration goals, they involve intensive and integrated pest management regimes, and activities, results and outcomes are closely monitored. Unlike true islands which are surrounded by water, Mainland Islands are located on the main (North and South) islands of New Zealand and lie adjacent to other areas not managed intensively for conservation purposes.

Because of the interrelationships between Mainland Island sites and their surrounding landscapes the “island” analogy is not definitive in a biogeographic context. The use of the term stems from the presence of obvious borders at some projects located in forest remnants within pastoral landscapes. Intensive pest control to limit the movement of pests into managed areas has been focused at forest–pasture margins in the same way that surveillance, quarantine and contingency measures are focused around the coasts of pest-free true islands. The “island” analogy is even less relevant in relation to projects within habitat complexes where core management areas lie within a larger habitat continuum and management boundaries are less obvious. The term ‘Mainland Island’ is nevertheless evocative of a new generation of conservation projects aimed at restoring damaged ecosystems on the New Zealand mainland.

The “Mainland Island approach” is based on successes in removing herbivorous and carnivorous pests from offshore islands, and increasingly effective pest control programmes undertaken at mainland sites. Mainland Island pest control regimes are more intensive and have been maintained for longer periods than has normally been the case previously in New Zealand. In less than 5 years significant reductions in suites of targeted pests have been achieved and ecological changes have been attributed to the management applied. There are also indications that some of these projects have been important in educating people and empowering stakeholder involvement in conservation management programmes. While results suggest that these projects represent a new era in conservation management, major challenges remain to be addressed before comprehensive ecosystem restoration goals are achieved.

In this paper we outline the background to the emergence of Mainland Island projects on the New Zealand mainland, identify new challenges they present and discuss how they might contribute to future biodiversity conservation programmes.