New Zealand lies on two tectonic plates with edges that rub against each other. The resulting earth movements produced hilly and mountainous terrain over two-thirds of the land, with frequent earthquakes in most parts of the country and a zone of volcanic and geothermal activity. Much of the rock beneath our soils is relatively unstable, making the land prone to erosion. This instability is exacerbated by heavy rainfall in many regions, especially where the original forest was cleared and replaced with pasture. This is because grass is shallow-rooted and does not have the stabilising capability of deeply rooted trees. Our soils, which mostly evolved under forests, tend to be acidic with low levels of nutrients such as nitrogen and phosphorus.
Our mountainous terrain created fast-flowing rivers, which in times of heavy rain can breach their normal course and cause widespread damage to land. Climate change is also likely to bring more extreme weather in the future, leading to more flooding and erosion.
These natural pressures influence everything we do on our land – for example, agriculture and other primary production, urban and infrastructural development, and mining.
Humans have created additional pressures that affect land productivity and its ability to support biodiversity. These pressures will be discussed in this section.
This section describes two of the key pressures on our land: land use and pests.
Agriculture is the main land use with farming intensifying in some regions
Agriculture is a major contributor to our economy, but it has a considerable effect on the condition of our land and fresh water in New Zealand.
The area of pastoral farming (grazing of livestock) in New Zealand remained relatively stable between 1996 and 2012, but in some regions the nature of farming and its intensity have changed. These changes have put more pressure on land, and on our freshwater and marine environments.
Intensive farming is characterised by higher stocking rates, repeated cultivation, and increased inputs to produce more food from the same area of land. These inputs include fertilisers, supplementary feed, water for irrigation and livestock, pesticides, herbicides, and energy.
Dairy farming is the main driver of recent farming intensification. Between 2002 and 2012, the area of dairy farming in New Zealand increased 28 percent. Most of this expansion was made by converting sheep and beef farms, which decreased in area by almost 11 percent. (Note that sheep and beef farming covers a significantly greater area than dairy farming, so this percentage change translates into a larger area relative to dairy farming.) In some regions this change was more pronounced – dairy farm areas in Canterbury, Otago, and Southland doubled between 2002 and 2012.
For more detail see Environmental indicators Te taiao Aotearoa: Farm size.
As the area of dairy farming increased, stock numbers also rose. From 2002 to 2014, the number of dairy cattle (including bobby calves) increased 30 percent, to about 6.7 million stock (see figure 30).
Note: All livestock numbers calculated as of June each year. Dairy cattle figures include bobby calves. Deer figures for 2002 and 2003 are not included – they are not comparable with those from 2004 onwards due to a change in survey design.
This graph shows how the numbers of sheep, total cattle, dairy cattle, beef cattle and deer changed across New Zealand between 2002 and 2014. Visit the MfE data service for the full breakdown of the data.
Farming intensification also affects land productivity. The treading of cattle, especially in wet conditions, can compact surface soil, which reduces pasture growth and the capacity of the soil to hold water, resulting in greater run-off. The potential for compaction is higher when stocking rates increase or a shift to heavier stock is made.
While increased use of nitrogen fertilisers and higher stocking rates can increase production, nutrient leaching and run-off can degrade the ecological health of fresh water.
For information about these pressures on fresh water, including the extent and impact of changes in nitrogen fertiliser use, see: The pressures on our fresh water section.
Other land-use pressures
Urban expansion also affects the productivity of land and its ability to support biodiversity. Between 1996 and 2012, New Zealand’s area of urban settlement increased 10 percent. In the same period, our total population increased 18 percent, with most of that increase being in the Auckland region (53 percent), followed by Canterbury (11 percent), and Waikato (9 percent) (Statistics NZ, nd). Population growth and urban expansion, particularly when concentrated in specific areas, put pressure on our air, freshwater, land, and marine environments.
Expanding residential or rural residential areas (or lifestyle blocks) also affects land productivity – for example, by building on highly productive areas well-suited to producing vegetables, fruit, and grains.
For more detail see Environmental indicators Te taiao Aotearoa: High-class land for food production.
Animal and plant pests are the greatest threats to indigenous biodiversity and habitats in New Zealand. They also affect the productivity of agricultural and other productive land.
Of all animal pest species, possums, rats, and stoats are the most widespread in New Zealand. They are found across at least 94 percent of New Zealand, absent only from the tops of mountains and a few predator-free sanctuaries and offshore islands. Rats and stoats prey on indigenous birds, while possums eat large quantities of indigenous vegetation and prey on indigenous birds. Possums also pose a threat to the health of cattle and deer because they carry bovine tuberculosis.
From the available data we have for this report, we cannot draw any definitive conclusions about how their numbers and distribution have changed over time. However, we know that population ‘explosions’ of rats and stoats are associated with ‘mast’ events (ie when beech and other indigenous trees produce large amounts of fruit and seed). Rat and stoat populations can increase to up to five times their normal peak numbers in these masting seasons.
Feral goats and red deer are present in more than 30 percent and 57 percent of the country, respectively, mainly in forested and alpine regions. They do not pose as great a threat as the ‘big three’ (possums, rats, and stoats).
New Zealand has more species of exotic plants than indigenous ones. Many have become invasive in forests, tussock grasslands, wetlands, and other indigenous environments. Wilding pines (primarily Lodgepole pine and Douglas fir) have become one of our major plant pests in New Zealand. They can rapidly colonise tussock grassland or shrubland, become dominant, and make it less suitable as habitat for indigenous species. They are a specific problem in farmland and tussock grasslands in Canterbury and Otago.
Many introduced plants are also a nuisance on farms and forest plantations – they can poison or harm animals, clog irrigation channels, and smother crops.
For more detail see Environmental indicators Te taiao Aotearoa: Land pests and Modelled rat and stoat population responses to mast-seeding events.