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Restoration strategy and project implementation
The Restoration Strategy confirmed the goal of restoration and defined the conservation outcomes: representative fauna, flora and habitats restored in the enclosed area; indigenous character of the valley restored; key natural processes functioning; species dispersal and gene-flow occurring; knowledge and methodologies gained for application elsewhere; and contribution to national recovery programmes.
To meet these outcomes general policies were developed in 10 areas, including for example:
- translocation to be used to replace missing species
- species to be sourced from the nearest geographical populations able to be sustainably cropped
- extinct species could be replaced by analogues
- where appropriate all management techniques available to be used (eg supplementary feeding and artificial nest boxes)
- public feeding of birds to be discouraged
- habitat manipulation permitted within the constraints of management zones defined in the Management Plan
- all transfers require the consent of the Department of Conservation and support of affected landowners and local iwi - to obtain consent from the appropriate parties each transfer has to meet strict ecological criteria and often requires comprehensive disease screening.
The Restoration Strategy provides the framework for the restoration of both forest and freshwater ecosystems, listing the species and habitats thought to be appropriate to the valley and identifying activities to be undertaken to achieve a successful outcome. The artificial dams are of historic importance so are permanent, so the two lakes are treated in the Strategy as if they had been caused by a natural stochastic event, allowing for the “restoration” of a representative diverse range of freshwater fauna and flora.
The first and arguably the most important component of the Trust's restoration programme to be implemented was the construction and maintenance of a pest mammal exclusion fence. This was completed in 1999 and by January 2000 all mammalian pests had been successfully eradicated in the first attempt to do this as a single operation. All vehicles, bags and equipment are checked prior to entry in the sanctuary to minimise risk of accidental introductions, but mice have been able to exploit flaws or damage to the fence. We have always assumed that the fence will never be effective 100% of the time (even offshore islands are at risk from accidental introductions), so we have audit and control response procedures in place. Read more about our pest eradication.
Weed control and progressive removal of exotic trees has been underway since 1998, with particular emphasis on removal of the largest trees located nearest the fence, and weedy species that threaten the integrity of the forest. A plant nursery has been established for the propagation of rare and missing species, and these are planted into appropriate habitats in the sanctuary as they become available. Read more about our flora restoration.
While the removal and exclusion of mammalian pests benefited resident species, many species were locally extinct so transfers have been undertaken since 2000. The first species released were flightless birds, including the smallest species of kiwi returned to the mainland for the first time in over 100 years. Then other species of birds were progressively released that could coexist with mice inside the sanctuary, with rarer species such as saddleback and hihi/stitchbird returned to the mainland for the first time in over 100 years in 2002 and 2005 respectively. Each transfer built on the knowledge gained about releasing birds into a valley where the fence provided no barrier to dispersal. Supplementary feeders and nest boxes have been used during the establishment phase for some species; others have established without additional assistance.
Following on the success of bird reintroductions, transfers of tuatara, Maud Island frogs and Cook Strait giant weta have been undertaken, bringing these species back to the mainland for the first time in over 100 years, and allowing us to determine if they can coexist with mice. Each transfer has been monitored thoroughly and undertaken with an experimental approach if possible, to maximise the knowledge gained about the requirements for a successful transfer; the techniques developed have been used in subsequent releases here and elsewhere. Read more about our fauna restoration.
The implementation of the restoration strategy has largely been focused on the terrestrial ecosystem; the next challenge is the removal of pest fish from the streams and lakes and restoration of native fish. Read more about our wetland restoration.
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