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The state of our land

In this section, we provide information on the condition of the land environment and how it is changing over time. We measure this condition through indicators such as land cover, extent of erosion, soil health, the conservation status of indigenous animals and plants, threatened land environments, and the distribution of indigenous trees.

Land cover

Nearly 40 percent of New Zealand is exotic grassland (primarily pasture used to graze stock). This percentage remained relatively stable between 1996 and 2012 (see figure 31).

Mature indigenous forest and regenerating forest (‘broadleaved indigenous hardwoods’ in table 2) cover 26 percent of the country. Most of this forest and regenerating forest is concentrated in hill and mountain areas, with little lowland forest remaining. Tussock grassland covers 8.7 percent of the country, mostly in the high country of Canterbury and Otago.

Plantation forest covers 7.5 percent of total land area, while crop lands, orchards, and vineyards account for 1.8 percent. Urban settlements cover 0.8 percent of total land area.

The first New Zealand-wide assessment of land cover using satellite imagery was in 1996. Between 1996 and 2012, three areas increased:

  • exotic forests (up 11.5 percent or 208,000 hectares)
  • urban areas (up 10.1 percent or 21,000 hectares)
  • cropping/horticulture (up 9.6 percent or 41,000 hectares).

A decrease of more than 10,000 hectares in indigenous forest and regenerating forest (broadleaved indigenous hardwoods in table 2) occurred during this period. While this represents a small change (0.26 percent) in statistical terms, it is ecologically significant because any loss in forest also leads to a loss in ecosystems and the plants and animals that inhabit these ecosystems. Once indigenous forest is lost, it is difficult to restore.

Table 2:           Area of land cover by main land-cover classes

Class

Area (hectares) 2012

Percent of total land area 2012

Percent change 1996–2012

Indigenous forest

6,390,000

23.8

–0.2

Broadleaved indigenous hardwoods

587,000

2.2

–1.2

Scrub

1,538,000

5.7

–3.1

Tussock grassland

2,338,000

8.7

–1.3

Alpine vegetation

653,000

2.4

 0.1

Other indigenous vegetation

335,000

1.2

–1.3

Exotic forest

2,020,000

7.5

 11.5

Exotic grassland (pasture)

10,675,000

39.8

–1.6

Cropping/horticulture

473,000

1.8

 9.6

Urban

227,000

0.8

 10.1

Bare ground

957,000

3.6

 0.2

Snow and ice

111,000

0.4

..

Water

537,000

2.0

 0.5

Source: Landcare Research

Note: ‘Scrub’ includes both indigenous (eg kānuka and mānuka) and exotic species (eg gorse and blackberry). ‘Broadleaved indigenous hardwoods’ is regenerating forest that has not yet recovered its tall dominant (typically conifer) species.

Total area of New Zealand calculated to 26,842,403 hectares. All areas rounded to nearest 1,000. Percentages are calculated using unrounded figures.

Symbol: .. figure not available. The area of snow and ice was calculated in 1996 and was not recalculated for land cover. For more information on glacier extent see: Atmosphere and climate chapter.

Figure 31:


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Note: Data is from the reclassified New Zealand Land Cover Database version 4.0.

This map illustrates the distribution of land cover classes across New Zealand in 2012. Classes mapped include, indigenous forest, broadleaved indigenous hardwoods, scrub, tussock grassland, alpine, other indigenous vegetation, exotic forest, exotic grassland, cropping and horticulture, urban, snow and ice, bare ground, and water. Visit the MfE data service for the full breakdown of the data.

Land stability and soil health

The condition of soils underpins the productivity of our land. This section examines three aspects of land and soil health – long-term soil erosion, the extent of land at risk of severe erosion, and soil health.

Human-caused soil erosion is higher in the North Island’s north and east

Soil erosion reduces the productivity of land and limits future land uses. It also affects fresh water, as most eroded soil eventually washes into waterways and then out to sea. This affects water quality and the ecological health of rivers, streams, lakes, estuaries, and coastal environments. For more information see: The pressures on our fresh water section.

New Zealand loses around 190 million tonnes of soil into waterways and the ocean every year. This is estimated to contribute about 1.5 percent to global sediment loss, despite New Zealand making up only 0.2 percent of the global land area (Syvitski et al, 2005; Walling, 2008).

Gisborne has the highest rate of erosion in New Zealand, at about 4,800 tonnes per square kilometre annually, followed by the West Coast and Northland (2,100 and 1,160 tonnes per square kilometre, respectively) (see figure 32).

The North and South islands have high rates of soil erosion, but what causes this is different for each island. Soil erosion in the North Island occurs mainly in areas of hill country cleared of forest, often triggered by heavy rainfall. This also happens in the South Island but to a much lesser extent. In the South Island, serious erosion is due mainly to natural processes, such as rain and natural erosion, especially along the Southern Alps. Much of this land is in the public conservation estate or is extensively farmed land of low productive value, so the impact of such erosion on productivity is generally of less concern.

Nationally, we have no historical data for the average rates of erosion, and therefore cannot conclude whether erosion is increasing or decreasing. However, modelled data from Dymond et al (2010) suggest a downward trend in the extent of soil erosion since the early 1980s. They attribute this to an increase in plantation forestry and scrubland on land formerly used for agriculture.

Besides areas of actual erosion, 840,000 hectares of land have been identified in the North Island as being at risk of severe erosion. This assessment is based on land gradient, the presence of woody vegetation, and rainfall in the area. The extent of potentially erodible land was mapped only for the North Island because it has the greater risk from human-caused erosion. While this happens also in the South Island, it is not considered to be a widespread problem compared with the North Island. Regional councils and the Ministry for Primary Industries use this information to prevent erosion on susceptible land before it occurs.

For more detail see Environmental indicators Te taiao AotearoaEstimated long-term soil erosion and Estimated highly erodible land in the North Island.

Figure 32:


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Note: Stewart Island is not mapped for erosion.

This map illustrates the distribution of estimated long-term soil erosion across New Zealand in 2012. Visit the MfE data service for the full breakdown of the data.

Most soil is in good condition but compaction is a problem on many dairy and dry-stock farms

Most of the soil surveyed by regional councils between 2009 and 2013 was in good condition overall, but compaction is a problem on many dairy and dry-stock sites. Councils measured 420 sites under four types of land use (cropping/horticulture, dairy, dry stock, and forestry) against soil health targets for acidity, fertility (phosphate available to plants), organic reserves (carbon, nitrogen, and mineralisable nitrogen), and physical status (how compacted the soil is).

More than 90 percent of sites met the targets for acidity, while the majority of sites met the targets for organic reserves and fertility (see figure 33). However, only 23 percent of dairy sites and 39 percent of dry-stock sites met the target for physical status (meaning they had high levels of compaction).

Figure 33:

Soil sites within target range for given soil health indicators

Click image to view full size

This graph shows the percent of soil sites sampled that were within target range for acidity, organic reserves, fertility, and physical status, under forestry, cropping and horticulture, dairy, and dry stock land uses in 2011. Visit the MfE data service for the full breakdown of the data.

A high degree of compaction affects productivity because plant roots need spaces between soil particles to grow, while soil organisms need this space to ‘breathe’. Compacted soils are often slow-draining, becoming water-logged when wet. This can lead to run-off and soil erosion (Mackay, 2008).

Compaction is generally caused by machinery or trampling by stock. The extent of compaction depends on many factors – the size and number of stock, the amount of organic matter (which makes soil more resilient to compaction), and moisture in soil (wetter soils are more prone to compaction).

Of all soil health problems, compaction is the hardest to remedy. High acidity can be addressed by adding lime; low fertility levels can be supplemented by adding phosphate fertilisers; and low organic reserves by applying nitrogen fertilisers. In contrast, the best way to address compaction is to ‘rest’ the soil, which takes time.

For more detail see Environmental indicators Te taiao AotearoaSoil health and land use.

Indigenous ecosystems and species

This section presents information on the state of our indigenous ecosystems – the threat status of indigenous plants and animals, the condition of our indigenous environments, and the populations of common forest trees.

Many indigenous plants and animals are at risk of extinction

Despite conservation efforts, many indigenous plants and animals are at risk of extinction, and for a substantial number of these, the risk is increasing.

Of 2,378 indigenous vascular plants, 235 are threatened with extinction and 683 are at risk (ie they are not currently threatened with extinction, but risk becoming so). Combined, this represents nearly 40 percent of our indigenous vascular plant species (de Lange et al, 2013). Seventy-two percent of our indigenous freshwater fish are at risk or threatened (Goodman et al, 2014). Freshwater habitats are directly affected by the way we use land – through discharges of effluent from industrial and urban sources; run-off from farmland; dams and other barriers to migration; and clearance of vegetation along waterways. Of our 203 living bird species, more than 80 percent are now threatened or at risk. Many are marine birds, but all birds roost and breed on land where they are prey to rats and mice (Robertson et al, 2013). Our lizard species are also decreasing – nearly 90 percent are threatened or at risk (Hitchmough et al, 2013).

The extinction risk for a number of land species worsened between 2005 and 2011, including 30 plant, 11 bird, and one bat species. The extinction risk for eight species of birds, three species of weta, and one bat species improved.

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

Remaining indigenous environments are not representative of original extent

Nearly one-third of our land environments have less than 10 percent of their indigenous cover, while 46 percent have less than 20 percent remaining. Scientists have identified 500 land environments, representative of all of New Zealand, based on their landforms (terrain and topography), soils, and the climates that influence them. Land environments help us understand the unique characteristics that shape localised environments, producing distinctive ecosystems and habitats for plants and animals.

Our most threatened indigenous environments are in coastal and lowland areas, particularly in the east of the South Island and most of the North Island (see figure 34). While New Zealand has relatively large areas of beech forest in mountainous areas of both islands, it has only small proportions of its coastal, wetland, and lowland forests remaining. These forests, often referred to as podocarp/broadleaf forests, are characterised by podocarp species such as rimu, tōtara, and kahikatea, and broadleaf species such as pukatea and rātā. In the north of the North Island, only a few kauri forests remain.

This measure of vegetation cover (also known as ‘threatened environments’) does not distinguish between forms of indigenous vegetation. This means that any form of indigenous vegetation is included in the assessment – not just the vegetation originally associated with the environment. For example, kānuka/mānuka scrub is considered indigenous vegetation, even if it is in environments where lowland mixed podocarp forest once grew. Therefore, the vegetation and ecosystems associated with some environments may be more at risk than this measure indicates.

Figure 34:


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This map illustrates the distribution of indigenous vegetation remaining in land environments across New Zealand in 2012. Visit the MfE data service for the full breakdown of the data.

For more detail see Environmental indicators Te taiao AotearoaIndigenous cover and protection in land environments and Rare ecosystems.

Common indigenous tree populations are stable

The populations of common indigenous forest trees have been stable for about 10 years. The presence of a widespread species is an indicator of general forest health across the country. A species’ age structure is one factor that helps us understand the overall health of indigenous forests. Just like the human population, an imbalance in birth and death rates may indicate that something is disturbing the normal cycle of growth.

Forests are surveyed across New Zealand to monitor the carbon they capture and store. Data about biodiversity is also gathered as part of this work. The population structure of eight common tree species was assessed in two survey periods – in 2002–07 and 2009–14 (see figure 35). The information came from 869 sampling plots across public conservation land and private land. Because deer, goats, and possums eat these eight species, their population structure tells us about the extent of damage caused by these pests and the effect on the rate of regeneration of each species.

Nationally, the population structure of the indigenous forest trees surveyed was stable between the surveys. No significant changes occurred in the number of trees per hectare for the eight tree species investigated in the two surveys (see figure 35).

Figure 35:


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Note: Error bars represent standard error. Surveys with overlapping error bars are unlikely to be significantly different.

This graph shows the average number of trees per hectare for eight widespread tree species (lowland five-finger, mountain five finger, kohekohe, lowland tōtara, southern rātā, pate, broadleaf, and uplant tōtara) sampled in two periods, first between 2002 and 2007, and again between 2009 and 2014. Visit the MfE data service for the full breakdown of the data.

These results suggest that, for the eight tree species surveyed, just as many trees are becoming established as are dying, and therefore, on a national scale, indigenous forests are maintaining their ability to regenerate. However, some tree species are more vulnerable to pests than others. Deer, goats, and possums prefer to eat certain tree species, which may cause the tree to die. In the long term, this affects populations of these tree species, and can lead to them becoming locally extinct. This can affect the forest overall, adversely affecting its suitability as a habitat for some animal species.

For more detail see Environmental indicators Te taiao AotearoaStatus of widespread indigenous trees and Pest impacts on indigenous trees.

Ecosystem function

We have limited data on how well our forests and other land environments function from an ecological perspective, but have information about the carbon captured by our forests. Plants capture carbon through photosynthesis, so the ability of forests to capture and store carbon provides an indication of how well forests function as ecosystems. Carbon capture (or carbon sequestration) is an ecosystem service because it removes carbon dioxide (a greenhouse gas linked to climate change) from the atmosphere. We gather this data to report on greenhouse gas emissions as required by the Kyoto Protocol.

For more information see: Atmosphere and climate chapter.

Forests absorb carbon from the atmosphere

Our mature indigenous forests store an estimated 1,708 million tonnes of carbon – this amount changes little from year to year owing to the limited growth of these forests. Exotic and regenerating indigenous forests capture additional carbon, adding an estimated average of 8.2 million tonnes each year (calculated between 1990 and 2012; see figure 36). Because plantation forests and regenerating forests grow faster than mature forests, they capture more carbon than mature indigenous forests. When forests grow, their stocks of carbon increase.

Figure 36:


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This graph shows the estimated forest carbon stocks for mature indigenous forest, exotic forest, and regenerating indigenous forest between 1990 and 2012. Visit the MfE data service for the full breakdown of the data.

This sequestering function can have economic value when it is used to offset the cost of greenhouse gas emissions from other sectors such as transport, energy, and agriculture.

For more detail see Environmental indicators Te taiao AotearoaEstimated forest carbon stocks.