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National environmental indicators

See chapter 1, ‘Environmental reporting’, for more information on the core set of national environmental indicators and how they are used.

There are four national indicators for land. These indicators provide information on:

  • land cover

  • land use

  • soil health

  • soil intactness of erosion-prone hill country.

Reporting on changes in the land indicators, combined with other more detailed information about land use (such as trends in agricultural production and exotic forestry), will help identify some of the greatest pressures on New Zealand’s land.

Land cover

Land cover is an indicator of the state of our land.

Since 1997, land cover in New Zealand has been mapped periodically from satellite imagery to create the national Land Cover Databases (LCDB) 1 and 2 (see the ‘Ecological classifications’ section in chapter 1, ‘Environmental reporting’). The LCDB maps 43 different land-cover classes.

This chapter reports on the current state of and changes in land cover using LCDB land-cover classes in nine major groupings, as well as other agricultural production data.

Land use

Change in land use is an indicator of pressure on the land, but is not the same as change in land cover. For example, one land cover (for example, pasture) could be used for a number of land uses (for example, sheep, beef, dairy, or deer farming).

Land-use information can also provide information about land-use intensity, such as stocking rates and productivity.

Land-use maps, and estimates from the Agricultural Production Survey and the National Exotic Forest Description, are used in this chapter to report on national changes in land use and land-use intensity.

Soil health

Soil health (or soil quality) is the biological, chemical, and physical condition of different soil types under specific land uses.

The biological health of soil is determined by measuring the level of potentially mineralisable nitrogen in the soil.

The chemical health of soil is determined by measuring the levels of the following chemical compounds or properties of the soil:

  • carbon

  • nitrogen

  • pH

  • Olsen phosphate.

The physical health of the soil is determined by measuring macroporosity.

This chapter reports on the health of soils under New Zealand’s major primary production land uses (cropping, pastoral farming, and forestry).

To do so, this chapter draws on the results of a soil health monitoring project (the 500 Soils Project). The 500 Soils Project monitored six key measures of soil quality (see Table 9.2) across New Zealand’s 15 main soil orders (see Figures 9.1 and 9.2 and Table 9.1).

As part of the 500 Soils Project, the six key measures of soil health were monitored across seven major land-use categories (Sparling and Schipper, 2004; Sparling, 2007):

  • arable cropping (for example, grains and fodder crops)

  • mixed cropping (for example, vegetables)

  • drystock pasture

  • dairy pasture

  • tussock grasslands

  • plantation (exotic) forestry

  • native forests.

Table 9.2: Measures of soil health and information these provide

Measures

Soil health information

Biological properties

 

Potentially mineralisable nitrogen

Readily mineralised nitrogen reserves

Chemical properties

 

Total carbon content

Organic matter status

Total nitrogen content

Organic nitrogen reserves

pH

Acidity or alkalinity

Olsen phosphate

Plant-available phosphate

Physical properties

 

Macroporosity

Soil compaction, root environment, aeration

Data source: Adapted from Sparling and Schipper, 2004; Sparling, 2007.

Soil intactness of erosion-prone hill country

Erosion-prone land is mainly hill country with a slope of more than 21 degrees. The most erosion-prone hill-country lands are in pastoral land cover and have soils that are known as ‘yellow-brown earths’ situated on weakly consolidated mudstones and sandstones.

Land cover can be used to assess the soil intactness of erosion-prone hill country (that is, the ability of soils to stay in place on erosion-prone hill country).

This chapter reports on changes in pasture on erosion-prone hill country around New Zealand. To do so, hill-country pasture is identified from the LCDB, and its erosion potential graded as ‘severe’, ‘very severe’, or ‘extreme’ depending on its slope, the underlying soils, and any limits to land-use capability (land-use capability describes the capacity of land to sustain permanent primary production).

Other forms of soil erosion, such as wind erosion, are not discussed in this chapter.