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Impacts on biodiversity

This section describes the key impacts on biodiversity in New Zealand: the impacts on habitats and ecosystems, the effects of pests and weeds on biodiversity, impacts on species diversity, and impacts across domains.

Impacts on habitats and ecosystems

We have already lost a large proportion of our forests and other indigenous vegetation

An estimated 80 percent of the country was forested before humans arrived in New Zealand. Since then, milling and fire have destroyed much of our indigenous forest. Today, indigenous forest covers less than one-quarter of the country, mainly in mountainous areas. In coastal and lowland areas, much of the remaining forests are in small and isolated fragments.

The remaining indigenous forests and other vegetation do not represent the full range of ecosystems. For example, the loss of forests and other indigenous vegetation in coastal and lowland areas has adversely affected biodiversity – an estimated 57 percent of our threatened plant species grow in these environments (de Lange et al, 2004).

Although the rate of loss of indigenous forests has slowed, it has not stopped. Between 1996 and 2012, we lost a further 10,000 hectares of indigenous forests. While this represents a small change (0.26 percent) in statistical terms, it is ecologically significant – any loss of forest leads to a loss in ecosystems, and the plants and animals that live there. Once forest is lost, it is difficult to restore.

For more detail see Environmental indicators Te taiao AotearoaLand cover and Predicted pre-human vegetation.

Ecosystems that were once widespread continue to decline

Wetlands and active sand dunes were once widespread, but are now significantly reduced. These ecosystems support unique communities of plants and animals, and provide ecosystem services.

Active sand dunes are dunelands shaped by wind-blown sand. They support unique species of plants and animals, some of which face extinction (eg the New Zealand iris and some snail, moth, and butterfly species). Active sand dunes are affected by weeds that stabilise the dunes, changing their natural character and reducing their suitability as habitat for some indigenous species. Coastal development and rising sea levels also put pressure on sand dunes. They now cover less than 20 percent of the area they covered in the 1950s, and their loss continued to the most recent measurement in 2008.

Wetlands are also greatly reduced from their historic extent, mainly as a result of drainage for farming and settlement. Only an estimated 10 percent of wetlands remain from before European settlement. Wetlands provide flood protection, and filter and clean fresh water. They provide important habitat for biodiversity. For example, the Whangamarino wetland (one of New Zealand’s six wetlands of international importance) is habitat to about 400 different plant and animal species. Of these, 17 are classified as threatened, including one species of plant – the swamp helmet orchid (Corybas carsei) that lives only at Whangamarino.

For more detail see Environmental indicators Te taiao AotearoaActive sand dune extent and Wetland extent.

Many naturally uncommon ecosystems are threatened

New Zealand has 71 different rare ecosystems. These ecosystems are generally small (ranging from less than 1 hectare to 1,000 hectares), but each has distinct environmental conditions that support unique communities of plants and animals, many of which are rare and threatened. Therefore, they make a significant contribution to our national biodiversity. Almost two-thirds (45) of the rare ecosystems are classified as threatened under the red-list criteria of the International Union for Conservation of Nature (Holdaway et al, 2012). Of these, 18 (40 percent) are critically endangered, which means they are at the greatest risk of degradation and loss.

For more detail see Environmental indicators Te taiao AotearoaRare ecosystems.

Impacts of pests and weeds on our indigenous plants, animals, and ecosystems

New Zealand’s indigenous plants and animals evolved without predatory or browsing mammals. Humans introduced animals and plants that are now considered pests in the land, freshwater, and marine environments. Introduced pests have a major impact on indigenous biodiversity. They eat indigenous animals and plants, and compete with them for food or habitat.

Possums, rats, and stoats pose the greatest threat to our indigenous plants and animals (Parliamentary Commissioner for the Environment, 2011). These pests are present in at least 94 percent of New Zealand. Rats and stoats prey on indigenous birds, while possums eat large quantities of indigenous vegetation, and prey on birds.

Possums are the major cause of decreasing distributions of trees – such as pōhutukawa, Hall’s tōtara, kāmahi, māhoe, tawa, and rātā; they can also change the composition and structure of native forests (Payton, 2000; Nugent et al, 2010; Parliamentary Commissioner for the Environment, 2011). Possums destroy the nests of kererū and the North Island kōkako (Innes et al, 1999; Powlesland et al, 2003; Campbell et al, 2008). Possums have also been recorded killing sooty shearwater (tītī or muttonbird), the brown kiwi, kōkako, saddleback, Australasian harrier, fantail, and Westland black petrel (Brown et al, 1993; Sadlier, 2000).

Rats and mice have caused the declines or extinctions of many of our insects and lizards, including wētā, beetles, skinks, and geckos (Towns et al, 2006; St Clair, 2011;Newman, 1994). Like possums, rats and mice also slow forest regeneration by eating seeds and seedlings. The impact of ship rats on indigenous birds is clearly seen on Big South Cape Island near Stewart Island, which ship rats invaded in 1962. Rat populations grew rapidly, and within three years, nine species of birds declined or disappeared from the island, including the South Island saddleback, Stead’s bush wren, and the Stewart Island snipe. On the mainland, rats contributed to declines in populations of forest birds such as the North Island kōkako, kererū, kākāriki, yellow head (mōhua), and brown creeper (Innes et al, 2010).

The stoat is one the world’s most effective predators. Stoats are very agile, and are adept swimmers and climbers. In their average one-year life span, stoats occupy large home ranges and travel up to 70 kilometres in a fortnight. They are the principal predator of the kiwi: up to 60 percent of young kiwi are eaten by stoats (McLennan et al, 1996; Brown et al, 2015). Researchers filming kiwi nests have observed stoats repeatedly visiting burrows while the eggs were being incubated, waiting for the chicks to hatch. Stoats are a factor in the decline of threatened species such as the rock wren, black stilt, kākāpō, and the kōkako. Kākāpō and stitchbird (hihi) are now found only on islands or sanctuaries completely free of predators – they cannot survive where stoats are present (Powlesland et al, 2006; Department of Conservation, 2005).

Other pests, such as feral goats, red deer, and Himalayan tahr, have a more limited distribution, but when concentrated in large numbers, they can have significant effects on forest and alpine ecosystems.

Many introduced plants have become pests. The ‘wilding pine’ is a plant pest that has had a significant impact on indigenous ecosystems. These are introduced conifer species that spread beyond plantations or deliberate plantings, infesting indigenous ecosystems or farmland. Wilding pines grow much taller than tussock and shrubs, and when present in high numbers can dramatically change the nature of tussocklands and shrublands.

In our waterways, identified pests – nine fish, 11 invertebrate, and 41 plant species – have a significant impact on our rivers, streams, and lakes through predation, competition, and by altering freshwater habitats. For example, the algae didymo is now in over 150 South Island rivers. Didymo smothers and excludes aquatic plants and insects, and can substantially change stream ecology.

For more detail see Environmental indicators Te taiao AotearoaLand pestsFreshwater pests, and Marine pests.

Impacts on species diversity

New Zealand is a biodiversity hotspot but many species face extinction

New Zealand has the second-highest level of endemism for vertebrates in the world, after the Madagascar and the Indian Ocean Islands region. Vertebrates are animals with backbones, including bird, mammal, and amphibian species. Because of our high level of endemism, New Zealand is a ‘biodiversity hotspot’ (Mittermeier et al, 2004). Worldwide, only 35 countries and regions qualify as hotspots. These hotspots represent just 2.3 percent of Earth’s land surface but support 50 percent of the world’s endemic plant species and nearly 43 percent of endemic vertebrate species.

Many of our endemic species face extinction. For example, all our endemic marine mammal, frog,  and most endemic bat species are now threatened or at risk of extinction (Baker et al 2010; Newman et al 2013; O'Donnell et al 2013).

Extinction is an ongoing threat to many species

Many species face an ongoing threat of extinction. The extinction of one species can detrimentally affect other species or even entire ecosystems. Since humans arrived, hunting, habitat destruction, and introduced animals and plants have resulted in at least 40 species being confirmed extinct. However, the actual number of extinctions is likely to be substantially greater. For example, at least 70 New Zealand species or subspecies have not been seen for more than 20 years, but are still classified as ‘data deficient’ or ‘nationally critical (data poor)’, rather than ‘extinct’ (Hitchmough, 2013).

Table 3: Indigenous species that are threatened or at risk of extinction, by taxonomic group

Taxonomic group

Still living (number)

Threatened or at risk of extinction (number)

Threatened or at risk of extinction (%)













Freshwater fish




Freshwater invertebrates








Marine invertebrates








Vascular plants




Source: Department of Conservation; Threat Classification System 2012–14; Hitchmough et al (2013); de Lange et al (2013); Robertson et al (2013); Newman et al (2013); O’Donnell et al (2013); Goodman et al (2014); Grainger et al (2014); Freeman et al (2014); Buckley et al (2015).

Note: Excludes taxonomically indeterminate taxa, species that do not breed in New Zealand, and groups for which a recent threat classification is not available. In addition to the above species, 40 species are confirmed extinct.

Risk of extinction for some species still rising

For some species, the risk of extinction is increasing (see figure 41). The risk for about 7 percent (59 of 799) of our indigenous species worsened between 2005 and 2011, including birds, plants, freshwater fish, and marine mammals. In contrast, the risk of extinction for 12 species (1.5 percent of all species) improved (eg brown teal, yellowhead, and the Little Barrier giant wētā). These findings are based on assessments by the Department of Conservation since 2002, which evaluate the extinction risk of our indigenous species. The assessment uses the New Zealand Threat Classification System, which is similar to the International Union for Conservation of Nature (IUCN) Red List.

Figure 41:

Click image to view full size

This shows the number of threatened species that have changed conservation status, improving or worsening between 2005 and 2011. Visit the MfE data service for the full breakdown of the data.

For more detail see Environmental indicators Te taiao AotearoaChanges in the conservation status of indigenous species.

Impacts in one domain can affect biodiversity in others

Our environment is interconnected. Changes in the condition of one domain, such as land, can affect other domains, such as fresh water or marine.

Sedimentation of estuaries and coastal environments

The way we use our land affects freshwater and marine ecosystems. For instance, run-off from land can flow into waterways and into estuaries, affecting coastal ecosystems.

An example of this is the Kaipara Harbour catchment. Increased sediment in the rivers and streams flowing into Kaipara Harbour may affect snapper populations down the entire west coast of the North Island, from Cape Reinga to Wellington. Researchers analysed the chemistry of fish ear bones and found that almost all these snapper populations originated from the Kaipara Harbour (Morrison et al, 2009), where juvenile snapper live in horse-mussel beds and subtidal seagrass meadows. These habitats are affected by sediment flowing into the harbour from land in the wider catchment as a result of agriculture and other land uses (Morrison et al, 2014). Juvenile snapper are directly affected by sediment because it impedes their ability to find food and develop their gills (Lowe, 2013). This affects biodiversity, but also the ability to harvest these fish for recreational and commercial purposes.

Ocean acidity

What we do on land also affects the marine environment. Increased levels of carbon dioxide in the atmosphere, produced mainly by the burning of fossil fuels, is causing the acidity of our oceans to rise (Ciais et al, 2013). The ocean (and other water bodies) absorbs carbon dioxide from the atmosphere, which when dissolved, increases the acidity of water.

Ocean acidification will directly affect marine species and ecosystem processes. Plants and animals with calcareous shells (composed of or containing calcium or calcium carbonate), such as some plankton, snails, and corals, will find it harder to extract calcium carbonate from the ocean to build their shells (Secretariat of the Convention on Biological Diversity, 2014). Some plankton species have calcareous shells, and increased ocean acidity will slow their development and reduce their survival rate. This has the potential to have flow-on effects on the entire marine ecosystem. Plankton forms the base of the food chain and is a source of food (directly or indirectly) for almost all marine animals. Acidification has the potential to have widespread effects on marine ecosystems (Fabry et al, 2008).

Increased acidification may also affect our economic and social well-being. Some species that we harvest for customary, commercial, or recreational purposes, such as pāua, mussels, and oysters, will likely be affected by acidification.

For more information see: Marine chapter.

For more detail see Environmental indicators Te taiao AotearoaOcean acidification.