Executive summary

Te Kawau Tūmaro ō Tōi / Kawau Island's forest ecosystems, like many throughout Aotearoa / New Zealand have been severely degraded by introduced mammalian pest species. Though there are several pest mammals on the island, this primarily refers to four surviving species of wallabies introduced by Sir George Grey in the mid- to late-1800s. Te Kaunihera o Tāmaki Makaurau/Auckland Council's Regional Pest Management Plan (RPMP) identifies Te Kawau Tūmaro ō Tōi / Kawau Island as a strategic priority management area, aimed specifically at eradicating wallabies from the island to mitigate the risk they pose to ecosystems and primary industries across the region. The RPMP recognises that removing wallabies alone may cause unintended foodweb impacts and mandates a multi-species eradication programme which aims to remove these species from the island.

Referred to in this report as the pest free Kawau Island programme, the multi-species eradication programme is a collective effort, led by Te Kaunihera o Tāmaki Makaurau/Auckland Council with support of partners the Manuhiri Kaitiaki Charitable Trust and Te Papa Atawhai/Department of Conservation, and in collaboration with members of the community. To enable progressive implementation the programme has been split into two separate stages, the first of which commenced in Autumn 2025 and focuses on wallaby and possum browser removal. The second stage will focus on the removal of the island’s mammalian predators; however, future implementation is subject to feasibility assessment, approvals, community engagement and funding. If successful, the pest free Kawau Island programme would make Kawau the largest permanently inhabited island in Tīkapa Moana / Hauraki Gulf to become free of pest mammals.  

A forest monitoring network was established on Te Kawau Tūmaro ō Tōi / Kawau Island and will provide pivotal benefits to the pest free Kawau Island programme. This includes establishing a critical baseline of forest ecological integrity, highlighting current ecological issues, identifying trends associated with programme outcomes and informing adaptive management to improve overall success of the programme. This report describes a baseline snapshot of the current condition of dominant forest ecosystems on the island prior to the implementation of the pest eradication programme.

Overall, it is evident that the browsing pressure from wallabies and other mammalian pests has degraded the forest ecosystems, creating a recruitment bottleneck and arrested forest succession across much of Te Kawau Tūmaro ō Tōi / Kawau Island. The successful eradication of pest mammals shows strong potential to release these forests from their current degraded state. Positive signs, such as high indigenous dominance, high numbers of seedlings, and relatively intact bird communities, suggest a robust chance of forest recovery over time; however, recovery trajectories will likely vary significantly between ecosystem types, with kānuka-dominated areas and exotic forests potentially being slower to diversify than areas with existing broadleaved forest components. In addition, close monitoring of weed species will be essential, as the removal of browsing pressure may allow rapid expansion of exotic plants which are currently suppressed. The baseline data collected through this assessment provides a foundational snapshot of forest ecosystem health on Te Kawau Tūmaro ō Tōi / Kawau Island, allowing for future monitoring and adaptive management to ensure successful ecological outcomes from the ‘working towards a pest free Kawau Island’ programme.

Plot remeasures will be required over time to understand the outcomes of the pest free Kawau Island programme. It is recommended that in the short-term remeasures occur every two to three years post eradication to enable emerging pressures to be identified and mitigated; followed by a five-year frequency in the long term. Species-level population monitoring should also be considered to better understand outcomes of the pest free Kawau Island programme on the populations of high-value native species on the island.

Auckland Council technical report, TR2025/32

Auckland Council, December 2025