New Zealand straddles two tectonic plates whose edges are crunching against each other. The resulting earth movements have 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 in the central North Island.
Three quarters of New Zealand's land mass consists of geologically young sedimentary rocks which tend to be erodible. The known mineral resources are dominated by coal, gold, silver, and beach sand deposits of iron and titanium. Large amounts of sand, gravel and rocks are used for building, and limestone for fertiliser, building and other purposes. Economic exploitation of other minerals has been slight, though deposits of aluminium, uranium, halloysite clay, potassium and sulphur exist in recoverable amounts.
New Zealand's soils, which mostly evolved under forests, tend to be thin and acidic with low levels of nitrogen, phosphorus, and sulphur. As a result, nearly all soils used for crops and pasture need to be 'developed' and maintained with nitrogen-fixing legumes (e.g. clover), significant inputs of fertilisers, and often lime. In some areas, exotic planted forests also require fertilisers.
Since human settlement approximately 700-800 years ago, the indigenous forests, which once covered about 85 percent of the land area, have been reduced from some 23 million hectares to approximately 6.2 million (23 percent of the land area)-mostly confined to mountain areas and to some low-lying parts of the West Coast, Southland and Northland. In most areas lowland forests have been reduced to fragments and will need considerable expansion if the biodiversity within them is to be sustained.
Of the surviving indigenous forests, 4.9 million hectares are Crown-owned and 1.3 million hectares are privately owned. Most of the Crown forests are on fully protected conservation land (except for 150,000 hectares set aside for timber production on the West Coast). Most of the private indigenous forests are unprotected from conversion to other land uses, but timber production from them is subject to the sustainable management provisions of the Forests Act 1949 (except for 60,000 hectares set aside for economic purposes under the South Island Landless Māoris Act 1906, the management regime for which is currently under negotiation).
The biggest threat to the remaining forests comes from tree and seedling destruction by possums, goats and deer. These pose a serious risk to biodiversity on some 1.8 million hectares of Department of Conservation land. The Department runs pest control operations over about 1.3 million hectares and its pest control funding has been increased. Invasive weeds are also a threat and are subject to control operations.
Duneland ecosystems cover about 50,000 hectares, most of which have been heavily modified by grazing, fires, drainage, coastal development and introduced trees and grasses. A further 250,000 hectares of sand dunes are covered in pasture, pine forests or scrub. The inter-dune wetlands are among our most threatened ecosystems.
Grasslands covered 1-2 million hectares (roughly 5 percent of the land area) before humans arrived but expanded to almost 8 million hectares as a result of deforestation by early Māori fires. Further deforestation in the past 100 years by farmers and timber millers has extended the grassland area to 14 million hectares-over 50 percent of the total land area.
As introduced pasture grasses have expanded, the native grasses have contracted. Today, there are about 3.3 million hectares of 'tussockpredominant' grassland and nearly one million hectares of mixed scrub and tussock. Virtually all of this surviving tussock has been grazed, at least 1.5 million hectares have been degraded by sheep, rabbits and invasive weeds, and at least half a million hectares have been oversown with introduced grasses.
The proportion of New Zealand converted to farmland is large by world standards (52 percent compared to the world's 37 percent in 1993). Although our human population density is comparatively low (13 per square kilometre compared to the world's 43) our livestock density is high (180 sheep per km2 compared to the world's 14, and 35 cattle per km2 compared to the world's 10). This amounts to 13 sheep and 3 cattle for every person, and makes pastoral agriculture the country's main land use.
Although 14 percent of our land is physically able to support crops or horticulture, standing crops of all sorts (e.g. arable grain and fodder crops, market gardens, orchards and vineyards) cover less than 2 percent of this area (compared to the world's 11 percent). Conversely, the area devoted to pasture is twice the world average (50 percent compared to 25 percent).
Besides pastoral farming, the other major land use is forestry based on plantations of exotic conifers. These planted forests cover approximately 1.6 million hectares and are expanding over former farmland at a rate of about 70,000 hectares per year.
Because two-thirds of New Zealand consists of hills and mountains, areas of highly fertile soil and flat to gently rolling terrain are limited. Only about 31 percent of the land can sustain pastoral farming (grazing animals) without significant erosion controls. This includes the 14 percent which could also sustain cultivation. A further 28 percent can support restricted livestock grazing combined with tree planting, farm forestry or other erosion control measures.
Soil erosion has been accelerated in many areas since human occupation, by deforestation and inappropriate land use. National survey data collected in the 1970s, and more recent local studies, indicate that over half the country is affected by moderate to slight erosion. Nearly 10 percent has severe to extreme erosion, mostly concentrated in a few high risk areas (i.e. the eastern North Island, from Wairarapa to Gisborne, plus parts of Taranaki and the South Island high country).
No national data exist on other types of soil degradation, though carbon depletion, nutrient depletion and acidification may be widespread, and compaction and contamination appear to be common but localised.
An estimated 7,800 urban and industrial sites may be chemically contaminated, some 1,500 seriously. Sites associated with contaminating activities include landfills, service stations, sawmills, timber treatment plants, railway yards, engine works, metal industries and chemical manufacturers.
Several thousand of the nation's 80,000 farms, orchards and market gardens may have contaminated sites (e.g. old sheep dips, farm landfills), though no instance of extensive and serious contamination is known. In addition, some orchard soils have heavy metal residues from fungicides and some farms have DDT residues. The latter are well managed and rarely enter the livestock or human food chain.
Among the main land-use issues in New Zealand are:
the decline in ecological processes and biodiversity caused by habitat fragmentation in agricultural and urban areas;
the impacts of pests and weeds, especially possums, on ecosystems, crops and livestock;
the loss of agricultural soils for productive use in North Island hill country and South Island high country;
the degradation of 'elite' soils by the impacts of intensive farming;
the loss of 'elite' soils to urbanisation;
the loss of wetlands to land drainage; and
the degradation of waterways by run-off from farms, urban streets and subdivisions, and industrial discharges.
The main laws controlling the environmental effects of land use are the Resource Management Act 1991 and the Conservation Act 1987, the former requiring sustainable management and the latter conferring protection on gazetted areas. Other legislation requires sustainable logging in native forests, coherent strategies for pest control and the safe handling of hazardous substances and toxic sites.
Land users, with assistance from regional councils, the Government's Public Good Science Fund and environmental grants, are playing an increasingly active role in developing sustainable land management programmes and codes of practice (e.g. through community-based organisations, including 'landcare' groups, Federated Farmers, and the Forest Owners' Association).
Although much of the information on the national state of our soils, vegetation, and land ecosystems is out of date, incomplete, fragmented or poorly referenced, initiatives are under way to redress some of these deficiencies. They include:
the Ministry for the Environment's National Environmental Indicators Programme which includes the development of a core set of "state of the land" indicators;
the National Sustainable Land Management Strategy being coordinated by the Ministry for the Environment;
the National Science Strategy for Sustainable Land Management being developed by the Ministry of Research, Science and Technology (MoRST);
the updating of the New Zealand Land Resource Inventory by Landcare Research;
the collation of existing data in Landcare Research's Spatial Database Index;
the Biodiversity Assessment Programme being developed by Landcare Research; and
the development of a national land cover database derived from satellite imagery by Terralink NZ Ltd (formerly part of the Department of Survey and Land Information).
Initiatives are also under way to improve the information base for land managers at ground level. Monitoring programmes and extension services of regional councils play a key role, as do the information networks developed by land user organisations. In addition, the Ministry of Agriculture is developing sustainability indicators to assist farmers. Other research and information projects for better land management are funded through the Government's Public Good Science Fund, the Ministry for the Environment's Sustainable Management Fund and the Ministry of Agriculture's Sustainable Agriculture programme.