Chatham Island Temperate Forests
Chatham Island Temperate Forests, located in the Pacific Ocean off the coast of New Zealand, are characterized by their remarkable biodiversity and high rate of endemism. These forests evolved in a temperate climate that is typically cool, cloudy, and windy, which has shaped the unique adaptations of the local flora and fauna. Among the five distinct forest habitats found on the islands are the akeake, mixed broadleaf, and kopi-broadleaf forests. The ecosystems here are home to several endemic species, including the endangered Black Robin, and an array of insects that play crucial roles in pollination and decomposition.
Despite their ecological significance, these forests face serious threats from human activity, including deforestation for agriculture and the introduction of invasive species like the Argentine ant. Conservation initiatives have been increasingly important over the past four decades and are aimed at restoring the forest ecosystems and protecting the vulnerable species that inhabit them. Climate change poses additional risks, such as increased rainfall and stronger winds, potentially leading to habitat erosion and degradation. Currently, there is no formal protected area for the Chatham Island temperate forests, highlighting the urgent need for continued conservation efforts to safeguard this unique environment for future generations.
Chatham Island Temperate Forests
- Category: Forest Biomes.
- Geographic Location: Pacific Ocean.
- Summary: Located off the coast of New Zealand, the ecosystem of Chatham Island features high species diversity, which had deteriorated under invasive pressures but is slowly beginning to recover.
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 40 rock stacks and islets. Various ecosystems are associated with the archipelago, including forests, dunes, cliffs, and peats. 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 approximately half that of mainland New Zealand. The climate has produced adaptations in many of the plants, with 47 of the 388 indigenous flowering varieties endemic to the archipelago. The interaction of such species, and 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 over the past 40 years, and species that might have otherwise disappeared are now recovering.
Biodiversity
The high rate of endemism in plants here is primarily due to the absence of several of the dominating 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, tarahianu, 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.
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 current survival is dependent on them. The islands experienced a similar settlement trend to that of the New Zealand mainland, with the indigenous populations, the Moriori, arriving on the archipelago from about 800 to 1000 B.C.E., European discovery in 1791, and Māori settlement shortly afterward. Before the Moriori, more than 90 percent of the archipelago's landscape was a mosaic of forest, scrub, and swamp, but the majority of this land cover has since been transformed for agricultural purposes. Although agriculture puts pressure on many of the forest floral 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 has even been shown to outcompete the kiwi (family Apterygidae) for food on mainland New Zealand. 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 fro,m the absence of one dominating species.
An effort is underway to remove the Argentine ant from the archipelago; initiatives have been directed toward creating awareness among people traveling to the Chatham Islands from mainland New Zealand—including searches of picnic baskets, baggage, and other items. 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 imperative 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.
According to a report released in 2009 by the United Nations Environment Programme World Conservation Monitoring Centre (UNEP-WCMC), there is no current protected-area coverage for the Chatham Island temperate forests. This compares to an average of 12.3 percent for other island ecosystems. Many of the conservation efforts on the archipelago are overseen by the New Zealand government, with the two government-owned islands, Mangere and Rangatira, identified as conservation hot spots. Both islands are undergoing reforestation.
Bibliography
Dawson, J. W. "New Zealand Botany with a Difference—The Chatham Islands." Tuatara, vol. 31, no. 7, 1991, pp. 23-31.
Klages, Johanne P., et al. "Temperature Rainforests near the South Pole During Peak Cretaceous Warmth." Nature, vol. 580, 1 Apr. 2020, pp. 80-86, doi.org/10.1038/s41586-020-2148-5. Accessed 2 Nov. 2024.
Miskelly, C. Chatham Islands: Heritage and Conservation. Canterbury University Press, 2009.
Mullan, Brett, et al. Chatham Islands Climate Change. Ministry for the Environment, 2005.
Wardle, P. Vegetation of New Zealand. Cambridge University Press, 1991.