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Topic 2: Biodiversity

Biodiversity is the biological variety of plant and animal life, represented by existing species within terrestrial, and marine or other aquatic ecosystems. It consists of three interlinked elements: species variety, genetic variation, and ecological diversity.

Biodiversity contributes essential products and services to human welfare and provides environmental and economic resilience. Maintaining biodiversity helps sustain the natural ecological processes on which life depends. It also underpins industries such as tourism and fishing. New Zealand has a large number of species that are found naturally only in this country, and is therefore a significant contributor to global biodiversity.

Before humans arrived in New Zealand, flightless birds were the only animals that browsed in forests, and two species of bat were the only land mammals. Māori and European settlers introduced more than 25 animal species, mostly mammals, now considered to be pests that threaten native species and habitats. The challenge to protect our borders from new pests that threaten our biosecurity is ongoing. People have further modified New Zealand’s biodiversity by clearing forests and converting land to pasture or exotic forests. Avoiding the adverse irreversible effects of human activity on ecosystems and the services they provide is a defining principle of sustainable development (see table 2.2).

Main results

The distribution of seven native ‘indicator’ species has declined over the three decades to 2007. Most of this decline is attributed to predation and competition from introduced pests and habitat loss. Between 2002 and 2005, the threat status worsened rather than improved for a greater number of native species. However, native land cover changed very little between 1997 and 2002.

Table 2.1
Biodiversity indicators – key results

Biodiversity indicators - key results.

What the indicators tell us

Number of threatened species (indicator 2.1)

Maintaining biodiversity is a significant challenge. Threatened species may require conservation to prevent their extinction. Valuing and protecting biodiversity is an important part of the Māori world view, embodied by the notion of kaitiakitanga, or guardianship of the environment.

This indicator reports changes in the threat status of native species for which sufficient data exists. It is estimated that New Zealand has at least 80,000 native species. However, deforestation, over-harvesting, habitat destruction, pollution, and the introduction of exotic animals and plants threaten the survival of many native species.

Between 2002 and 2005, the threat status worsened for 40 species and improved for only five. Of these 40 threatened species, 5 were previously classified as ‘not threatened’. In addition to these 40, seven were confirmed as extinct, although actual extinction may have occurred many years ago (see figure 2a).

In 2005, New Zealand listed 2,788 native species and other taxonomic units (groups of organisms) as threatened (see figure 2b), up from 2,372 in 2002.

Change in threat classification status of native species, December 2002–05.

Total threatened native species by taxonomic group, December 2005.

Distribution of selected native species (indicator 2.2)

Seven native species were selected for this indicator: five bird, one mammal, and one plant. All are at risk of extinction. The indicator shows the total hectares over which each species was found across four time periods – pre-human, 1840s, 1970s, and 2007 – with the exception of the wrybill bird, for which the earliest period is the 1900s. Changes to the distribution of these seven species can indicate changes to their different ecosystems or the presence of pest species.

Figure 2c shows that the distribution of all seven indicator species has declined from pre-human levels. Four species – the short-tailed bat; dactylanthus (a flowering plant); and two bird species, the mōhua (yellowhead) and kōkako – are now 5 percent or less of the pre-human range. Furthermore, since the 1970s the distribution for kōkako has decreased 90 percent, mōhua down 70 percent, dactylanthus down 32 percent, short-tailed bat down 25 percent, and kiwi down 20 percent. Except for the wrybill, the majority of these species are now found mainly on Department of Conservation protected lands.

Distribution of selected native species as a proportion of pre-human range, by selected time periods.

Area of native land cover (indicator 2.3)

Changes to the area and type of native land cover allow us to monitor biodiversity. Native species are particularly threatened by native habitat loss (see indicator 2.1). Native land cover includes vegetation as well as glaciers, rivers, and alpine rock.

This indicator measures the amount of native land cover in 1997 and 2002 by type (14 vegetation and 8 non-vegetation classes). The extent of the different classes of native land cover under protection varies substantially.

Between 1997 and 2002, the total area of native land cover decreased by an estimated 16,500 hectares (0.1 percent). Native vegetation declined by 17,200 hectares. In contrast, there was a gain of 700 hectares of non-vegetation land cover.

The land cover for five classes of vegetation remained the same size, while nine classes decreased. Two non-vegetative classes increased in area: lake and pond (up 700 hectares) and alpine gravel and rock (up 100 hectares). However, two other classes declined, and four remained the same size.

Figure 2d summarises changes in native land cover and specifically shows the four largest vegetation classes. The greatest declines were for the broadleaved native hardwoods (6,600 hectares, down 1.2 percent), and manuka and kanuka (5,400 hectares, down 0.4 percent).

Change in native land cover by land cover class, December 1997–2002.

Proportion of assessed fish stocks below target levels (indicator 2.4)

New Zealand has one of the largest marine environments in the world, with an exclusive economic zone covering more than 4 million km2. With the majority of New Zealand’s biodiversity being in the ocean, inadequately managed fishing activities can contribute to a decline in biodiversity – both of target species (caught for consumption) and non-target species (by-catch and accidental kill). Furthermore, the fishing industry is an important component of the economy, and the industry’s ongoing viability depends on sustainable harvesting strategies.

Under New Zealand’s Quota Management System (QMS) there are currently 628 fish stocks managed with the objective of maintaining a ‘maximum sustainable yield’.

Evaluating the status of fish stocks is inherently difficult due to the vast areas of ocean involved, the migratory nature of some species, and the physical similarities between species. In 2008, a total of 101 fish stocks were evaluated relative to target levels. This accounts for 69 percent of the total landings by weight and value, and represents the main commercial species. The proportion of fish stocks assessed as being below target levels increased from 15 percent in 2006 to 29 percent in 2008 (see figure 2e).

The Minister of Fisheries sets limits on the total weight of stocks that may be caught commercially each year. The limit was lowered from 595,469 tonnes in 2006 to 567,723 tonnes in 2008, in order to track natural fluctuations and/or to correct the effects of historical overfishing. Of the 29 fish stocks below target levels in 2008, three have been closed to fishing and the remainder have received reduced commercial catch limits.

Another response to halting declining marine biodiversity is the creation of marine reserves, of which there are now 33 covering nearly 13,000 km2.

Proportions of assessed fish stocks by assessment category, 2006–08.

Distribution of selected pest animal and weed species (indicator 2.5).

New Zealand has been described as “one of the world’s weediest countries” (Landcare Research, 2009) with over 2,000 non-native plants growing in the wild, many of which are considered invasive. As many of these species place similar pressures on the environment, this indicator reports the 2007 distribution of 10 species that are widespread and represent a range of threats to native biodiversity. However, there is not enough information to make an assessment on changes over time.

Several animal pests, such as stoats, possums, and mice, are found nearly everywhere in New Zealand. They are known to eat the young of threatened bird species and up to 95 percent of kiwi chicks in unprotected areas are killed by predators. Animal pests can also eat native seedlings and stifle forest regeneration.

Pampas grass, the most widespread plant pest being monitored, is found in over 11 million hectares (42 percent) of New Zealand. Japanese honeysuckle, a vine that can smother native forests, is distributed across more than 5 million hectares (see figure 2f). Other weeds suppress regeneration in forests.

The species reported in figure 2f are all found on land, but pest species are also found in fresh water and the ocean. By 2000, 19 species of exotic freshwater fish had established wild populations in New Zealand waterways. Seven of these species are associated with lake degradation (see indicator 4.4), and are now present in more than 300 locations. Between 1970 and 2004, there was also a significant increase in the number of freshwater sites where five major aquatic weeds were found. The didymo alga, first reported in 2004, has been confirmed in over 200 freshwater sites in the South Island.

Distribution of selected exotic weeds and pests, at 1 July 2007.

About the indicators

Number of threatened species (indicator 2.1)

Taxonomy is the classification of organisms into biological groups. A taxonomic group is made up of taxonomic units that can be represented by a species, sub-species, form, or variety.

The indicator reports changes to the threat status of taxonomic groups, using the 2002 New Zealand threat classification system, which has seven threat categories. The indicator excludes changes that are the result of new evidence or knowledge. The threat classification of a species may improve, yet remain threatened.

Of the species classified in 2005, only those for which sufficient data exists were listed.

There are a further 3,031 known species for which there is insufficient data to make a threat status assessment. The species assessed are biased towards those which are considered likely to be threatened.

Distribution of selected native species (indicator 2.2)

The information is from the Department of Conservation, which conducts species surveys within protected areas and on private land.

The seven native indicator species are:

  • short-tailed bat – one of two species of New Zealand’s only mammal
  • kiwi – flightless bird
  • kākā – large forest-dwelling parrot
  • kākako – North Island forest-dwelling wattlebird
  • māhua (or yellowhead) – small insect-eating bird of beech forests
  • wrybill – wading bird that breeds on South Island braided rivers
  • dactylanthus – parasitic flowering plant.

Area of native land cover (indicator 2.3)

The data is from the Ministry for the Environment (2007a), sourced from Landcare Research.

Proportion of assessed fish stocks below target levels (indicator 2.4)

The indicator uses the Ministry of Fisheries’ assessments of fish stocks, mainly made in May of each year with a small number conducted in November. For some species, assessments made in previous years were carried forward.

The Fisheries Act 1996 requires that fish stocks are managed so that they remain at or above a level that can produce the maximum sustainable yield (the largest average annual catch that can be taken without damaging future stock levels), or at a level that is not inconsistent with this objective.

In 2008, only 101 of the 628 fish stocks in the QMS had known status. The fish stocks of known status are weighted towards those with the highest landings or value, or those most at risk of being unsustainable. Caution is therefore required in interpreting the results as the data may not be representative of all 628 fish stocks. The increased number of fish stocks of known status, from 99 in 2006 to 101 in 2008, represents more than two additional stock assessments, because only 85 were assessed in 2007 and several assessments were ‘retired’ over this period because they became too old or uncertain.

Distribution of selected pest animal and weed species (indicator 2.5)

The data is from the Department of Conservation. The animal pest and weed distributions in New Zealand are as at 1 July 2007.

Table 2.2
Biodiversity indicators – defining principles

Biodiversity indicators - defining principles.

See part C for the complete list of defining principles for all indicators.

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