Biological diversity, or biodiversity, is the variety of biological life on earth. Biodiversity comprises:
genetic diversity – the genetic variety among individuals of a single species
species diversity – the variety of species within a particular geographical area
ecological diversity – the variety of ecosystems (such as forests, deserts, wetlands, grasslands, streams, lakes, and oceans), the communities within these, and the interactions between them.
This chapter covers native land-based and freshwater biodiversity. Marine biodiversity is discussed in chapter 11, ‘Oceans’.
Biodiversity in New Zealand
Given the wealth and uniqueness of New Zealand’s biodiversity, the country is internationally regarded as ‘one of the richest and most threatened reservoirs of plant and animal life on earth’ (Conservation International, 2007).
New Zealand makes an important contribution to global biodiversity, with an estimated 80,000 species of native animals, plants, and fungi. We have comparatively few native flowering plants and land-based vertebrates (animals with backbones).
High proportion of endemic species
As a result of 80 million years of evolution in isolation from other land masses, a large number of New Zealand’s native species are endemic – meaning they do not naturally occur anywhere else in the world (Organisation for Economic Co-operation and Development, 2007). All our frogs and reptiles, more than 90 per cent of our insects, about 80 per cent of our vascular plants (plants other than mosses, liverworts, and hornworts), and a quarter of our bird species are found only in New Zealand. By comparison, Great Britain, which separated from continental Europe only 10,000 years ago, has only two endemic species – one plant and one animal.
New Zealand’s biodiversity is important for other reasons as well. Our natural landscapes and unique native plants and animals have strongly shaped our national identity. For many, our distinctive flora and fauna contribute to our sense of belonging to this land. New Zealanders take pride in calling themselves ‘Kiwis’ after one of the country’s most well-known native birds.
Our native species are culturally important to Māori. For example, Māori have traditionally used a variety of native berries, roots, and fruits for food, for dyes and stains, and as medicines. The flowering and fruiting of some native species guided traditional planting and harvesting times and rāhui (periods when harvesting is restricted to allow a resource to regenerate).
Why biodiversity matters
New Zealand’s ecological biodiversity performs a number of important services: our ecosystems provide clean air and water, help decompose wastes and recycle nutrients, maintain healthy soils, aid pollination, regulate local climates, and reduce flooding. These ecosystem services help sustain the country’s primary production – farming, forestry, viticulture, and horticulture. One study valued the ecosystem services provided by nature each year at $46 billion (Patterson and Cole, 1999). Tourism in New Zealand depends largely on the conservation of our ecosystems.
To many people, the variety of natural life also has an ‘intrinsic value’ in its own right, independent of its usefulness to human society.
More about New Zealand’s known native species
There are an estimated 80,000 native species in New Zealand. Almost 55,000 of these have been identified, and about 30,000 have been scientifically described, named, and classified. Table 12.1 shows the number of native species currently known1 in New Zealand.
Table 12.1: Number of known native species in New Zealand, 2007
Protozoa (single-celled eukaryotes – organisms whose cells have membrane-bound nuclei)
Chromista (group of eukaryotes other than protozoa)
(1) This includes the numbers of described species plus known species that have not yet been described.
(2) The numbers given for bacteria are based mainly on cultured species in New Zealand. Some of these have not been broken down according to their environment; most are land-based.
(3) The numbers given for aquatic species of fungi are approximate.
(4) The totals provided do not equal the sum of the rows as there is some overlap due to different life-history stages in different environments (for example, aquatic larval stages and land-based adult stages).
Data source: Adapted from Gordon (ed), 2007.
Factors affecting biodiversity
New Zealand has experienced one of the highest extinction rates in the world (Hitchmough et al, 2002). Today, almost 2,500 known land-based and freshwater species of animals, plants, and fungi are classified as threatened in New Zealand.
Human settlement and landscape transformation
Before human settlement, New Zealand was largely forested below the alpine tree line. However, in little more than 1,000 years, much of the country’s landscape and ecosystems have been transformed. Fires, land clearance, intensive use of natural resources, and introduced plants and animals have had a cumulative effect on New Zealand’s native biodiversity.
While almost half of the native habitats and ecosystems that existed before human settlement remain in some form today, many of them have been modified. Most of the remaining unmodified habitats are in remote or mountainous areas or on offshore islands (Ministry for the Environment, 2004). Many of them have been (or still are) under pressure from introduced animal pests and weeds.
Over the past 200 years, much of New Zealand’s most accessible and productive land has been cleared or modified for a range of different land uses, such as agriculture, horticulture, roading, and human settlement. As a result, many of our lowland and coastal forests, lowland grasslands, wetlands, dune lands, and estuaries have been modified. These habitats and ecosystems are particularly at risk of being modified further if they occur on, or are adjacent to, prime agricultural and horticultural land (Ministry for the Environment, 2004).
Many of our lakes, rivers, and streams have been modified by dams, drainage, and irrigation schemes. Some of them are also affected by pollution from agricultural and urban areas, which alters the ecological processes that support downstream freshwater biodiversity.
Changes in land cover can illustrate the impact of human settlement on native habitats and ecosystems. Figure 12.1 compares the estimated land cover before human settlement with the type of land cover in New Zealand today. It shows the significant changes to land cover that have occurred in the intervening period. See chapter 9, ‘Land’, for further discussion of the changes in land cover in New Zealand.
The isolated evolution of New Zealand’s native species means many of them lack strategies to co-exist with or defend themselves against introduced competitors and predators . Introduced pest animals and weeds can therefore pose a serious threat to New Zealand’s biodiversity in both land and freshwater environments (Organisation for Economic Co-operation and Development, 2007).
Introduced pests, coupled with the loss of native habitats and ecosystems, have caused a substantial decline in New Zealand’s native plant and animal species .
More than 25,000 plant species, 54 mammal species, and about 2,000 invertebrate species have been introduced to New Zealand since it was settled. Nearly 2,000 exotic plant species are now established in the wild. Of the mammals introduced to New Zealand, a group of 31 species now dominates many of our landscapes.
While some of these introduced species, such as sheep and cattle, are cornerstones of New Zealand’s agricultural industry, others pose a threat to our native biodiversity. Browsing pests such as goats, deer, and Australian brushtail possums, which also prey on native animals (Atkinson et al, 1995), change the structure and composition of our forests and grasslands. Predators like rats, stoats, and cats hunt some of our rarest native animals. Introduced weeds can smother or overshadow native plants.
Without sustained control of such pests, many of New Zealand’s protected ecosystems are at risk of continued biodiversity loss.
New Zealand’s biodiversity is not only at risk on land. All freshwater ecosystems, such as streams, lakes, and wetlands, and the freshwater species within them, are influenced by the human activity that occurs on adjacent land and within estuarine areas. Pest species, reduced water quality, and sedimentation can adversely affect biodiversity in these ecosystems.
As an example, wetlands represent some of New Zealand’s most diverse ecosystems, but 90 per cent of their original area has been lost through changing land use. Wetlands currently cover fewer than 2,500 square kilometres.
Whether plants and animals are native to New Zealand or introduced, most can only survive within a certain climate zone. While most species are able to cope with normal climatic variations, climate change is expected to place additional pressure on many species, particularly those already at risk.
A changing climate is expected to disrupt sensitive food-chain relationships in some ecosystems. For example, there is already evidence in the northern hemisphere that as temperatures grow warmer, some bird species are hatching earlier in the year, when the flower or fruit on which they depend for nourishment may not yet be ready.
Climate-influenced shifts in habitat may also lead to changes in the distribution of species. For example, migration patterns may alter, and the available habitat for sensitive alpine species may diminish with the gradual recession of glacial or snow systems.
As temperatures and climate patterns change, New Zealand may also develop new biosecurity risks, with new tropical pests and diseases potentially becoming established here.
Since human settlement, many of New Zealand’s unique native species, such as all species of moa, the Haast’s eagle, and the huia, have become extinct. Many more of our native species are currently threatened, with our levels of threatened species rated among the highest in the world (Hitchmough et al, 2007).
Extinction risk is determined by classifying species using the Department of Conservation's Threat Classification System, which takes into account national distribution and abundance, as well as other variables. Table 12.2 shows the threat status of native species in this classification system.
In some species groups, a large proportion of native species are threatened. For example, all of New Zealand’s native frog species are threatened as a result of loss of habitats and predation. Diseases are probably also responsible for declines in some species, with a chytrid fungus and a ranavirus recently detected in some native frogs. Five out of six New Zealand bat species are endangered because of predation and loss of the large trees they require as roosts.
Table 12.2 indicates that not enough is known about some groups to reliably determine their threat status. For example, many fungi and plants are listed as ‘data deficient’, which means insufficient information is available to determine whether they are endangered.