Chatham Island Temperate Forests

The Chatham Islands lie some 500 miles (800 kilometers) east of the South Island of New Zealand. They consist of two large inhabited islands, Chatham and Pitt, and aboutb forty rock stacks and islets. Various ecosystems are associated with the archipelago, including forests, dunes, cliffs, and peatlands. The importance of forested ecosystems is in part due to their high rate of endemism, meaning species that are found nowhere else on Earth.

The climate of the archipelago is temperate, and is often filled with cloud cover, rain, and windy conditions. Rarely does weather give way to extremes; annual sunlight is lower than that of much of mainland New Zealand. The climate has produced adaptations in many of the plants, with 47 of the 388 indigenous flowering species endemic to the archipelago. The interaction of such species with the local birds, insects, and other animals makes the Chatham Islands temperate forests a unique and valuable ecosystem.

The impact of humans here is noteworthy, as deforestation and invasive species have altered the balance, potentially destroying it from within. Fortunately, conservation efforts have been put in place since the late twentieth century, and species that might have otherwise disappeared have recovered through sustained management practices. One example is the Chatham Island black robin (Petroica traversi), a forest bird whose population declined to five birds in 1980 and increased through intensive management.

Biodiversity

The high rate of endemism in plants here is primarily due to the absence of several of the dominant forest species associated with New Zealand, such as conifers and beeches, allowing locally evolved species instead to influence the landscape. Five main forest habitats exist that are unique to the archipelago: akeake, mixed broadleaf, kopi-broadleaf, tarahinau, and akeake/karamu swamp. The windy climate has resulted in the tarahinau tree’s developing wind-resistant needle leaves, while numerous types of tree fern dominate the forest floor, providing shelter for tree seedlings to germinate.

Many of the endemic species exhibit gigantism traits, a feature that is common among some island populations of animals, and in the Chatham Islands among some plants as well. The forest tree koromiko and the forest shrub karamu, which matures into a tree, are represented by the largest species of their genus; the tree daisy akeake, too, is one of the largest of its kind.

Similar rates of endemism exist for insect and bird populations in the forests here, but there are no native mammals or amphibians, and there is only one indigenous lizard species.

The island of Rangatira is famous for its bird populations, and the forest on the island is also important to many insects. These species are often vital to forest ecosystems: pollinating, decomposing, and playing a key role in the food web. Rangatira is home to the Rangatira spider, giant click beetle, and numerous other native insect species. Approximately two-thirds of the flowering plants in the temperate forests here are pollinated by insects, which is higher on the Chatham Islands than in many other lands, due to the relative lack of indigenous mammals and birds.

Threats and Conservation

Although the Chatham Island temperate forests originally evolved without the influence of humans, their long-term survival is dependent on them. The islands experienced a similar settlement trend to that of the New Zealand mainland, with the  Moriori people arriving on the archipelago in the fifteenth century C.E., European discovery in 1791, and Māori settlement in 1835. Before the Moriori, the vast majority of the archipelago’s landscape was a mosaic of forest, scrub, and swamp, but much of this land cover has since been transformed for agricultural purposes. Although agriculture puts pressure on many of the forest plant species by fragmenting and restricting their ranges, this land cover change also has affected birds. More than half of the identified bird species inhabiting the archipelago have become extinct since the first human settlers arrived.

Another major threat to these forests is the introduced Argentine ant (Linepithema humile). This species outcompetes other insects for food and disrupts native invertebrate communities. The Argentine ant could potentially destroy the forest ecosystem from within, winning out over a large number of other insects that have evolved to occupy small niches left from the absence of one dominating species.

Because accidental transport can spread colonies, biosecurity initiatives aim to remove the Argentine ant from the archipelago. Measures include creating awareness among people traveling to the Chatham Islands from mainland New Zealand; inspecting their picnic baskets, baggage, and other items; and using detector dogs to detect these invasive species. The potential for one species of ant to alter the balance of this ecosystem is huge, and the mitigation strategies implemented on the islands are important for the forests’ survival.

Heavier rainfall events, higher sea level, and more extreme storm surges are among the impacts projected from global climate change here. Average temperature rise is anticipated to be slower than the global average, and thus less of a major factor on habitats in the Chatham Islands. Stronger westerly winds are projected; along with greater annual rainfall, this will mean western shorelines of the islands will be at substantial risk for wetlands degradation and inland-slopes habitat erosion.

Protected areas exist within the archipelago, including Rangatira and Mangere Islands, which are designated nature reserves and managed for conservation. Many of the conservation efforts on the archipelago are overseen by the New Zealand government, and these government-owned islands are identified as conservation hot spots. Both islands are managed with reforestation as a core objective. Conservation planning for Rangatira Nature Reserve and Mangere Island Nature Reserve incorporates an overlay classification established under the Moriori Claims Settlement Act 2021 and associated protection principles.

Bibliography

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“Detector Dogs with a Nose for Biosecurity.” Chatham Islands Council, 24 July 2025, www.cic.govt.nz/your-council/news-and-events/2024/detector-dogs-with-a-nose-for-biosecurity. Accessed 16 Feb. 2026.

Klages, Johanne P., et al. “Temperate Rainforests near the South Pole During Peak Cretaceous Warmth.” Nature, vol. 580, 1 Apr. 2020, pp. 80–86, doi:10.1038/s41586-020-2148-5. Accessed 16 Feb. 2026.

Miskelly, C. Chatham Islands: Heritage and Conservation. Canterbury University Press, 2009.

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Parker, Kevin A., et al. A Structured Decision-Making Approach for Recovery of the Karure / Kakaruia / Chatham Island Black Robin (Petroica traversi). New Zealand Department of Conservation, 2023.

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