What do rats, ants, and fast-growing plants like the african tulip tree have in common? They’re all invasive species threatening the unique wildlife and forests of Rarotonga.
Dr Tim Martin, Project ENUA Consultant, led a week of activities aimed at tackling these challenges, including two public consultation sessions and a two-day training on invasive species management. These sessions brought together landowners, tour operators, government staff and community members to explore practical ways to protect Rarotonga’s unique ecosystems.
During the public consultations, Dr Martin presented findings from recent surveys of the Rarotonga Forests Area, including the island’s cloud forests and upper catchments. These high-elevation habitats occur mainly along the ridges and summits of Te Manga and Te Ko’u, around 400–540 metres above sea level. The cloud forests are characterised by wind-swept shrublands with native plants such as neinei, rata, kiekie and kaiatea, while surrounding montane forests are dominated by native trees like mato.
The surveys showed that these forests are still in reasonably good health, but invasive species including trees, vines, ants and rats, are present and increasing in abundance. Some invasive trees, such as the african tulip tree, are currently less common on the summits than at lower elevations, which means there is still an opportunity to remove them before they cause major impacts.
Invasive plants can outcompete native species for light, nutrients and space, often forming dense stands that prevent native plants from regenerating. If left unmanaged, they can dramatically alter forest structure and even affect water supplies by reducing stream flows and lowering water quality.
Rarotonga’s forests are especially important because they support many species found nowhere else in the world. Endemic birds such as the kakerori and the Rarotonga fruit dove rely on these habitats but face threats from invasive rats. Native land snails are threatened by invasive ants, while endemic plants, including the Rarotonga Cyrtandra and Te Manga Cyrtandra, are vulnerable to aggressive invasive plants such as night-blooming cestrum and fast-growing vines.
One particularly unique species is the tiny land snail Tekoulina pricei, which is only known from the summit of Te Ko’u. It is threatened by invasive ants and is remarkable for giving birth to live young rather than laying eggs. The Rarotonga tree skink, another species found only on the island, is also at risk from invasive ants and rats.
Following the consultations, the two-day Project ENUA Invasive Species Management Training was held on 26–27 February 2026. Participants from Te Ipukarea Society, Climate Change Cook Islands, the Ministry of Agriculture and local catchment committees took part in sessions focused on monitoring and managing invasive species.
The field sessions in the lower portion of Te Manga were particularly eye-opening. Participants had the chance to practice using tracking tunnels to monitor rat activity and set up monitoring grids for ants—all with the goal of understanding the spread of invasive species, not trapping them. These tools are vital for detecting the presence of species and assessing how far they’ve spread. The group also observed the ongoing spread of invasive plants, further reinforcing the importance of monitoring and action.
Kuraiti Rasmussen, Senior Biosecurity Officer at the Ministry of Agriculture, highlighted the importance of collaboration in tackling invasive species across the Cook Islands. “This training reinforces the importance of collaboration and partnership to protect our natural environment from the growing threat of invasive species. By implementing effective surveillance and monitoring systems, and enhancing the skills of our local teams, we are taking practical steps to safeguard not only Rarotonga’s biodiversity, but the Cook Islands as a whole. The Ministry of Agriculture is committed to this alliance to ensure successful biosecurity management across all our islands.”
While controlling invasive species can be challenging, coordinated management, ongoing monitoring and community involvement will play a vital role in protecting Rarotonga’s forests and wildlife.
