Because human settlement in New Zealand has been so recent, widespread evidence of the environmental impacts can be found in sediments, bogs and archaeological sites. Early historical records, from Captain Cook onwards, provide information on both Māori and European interactions with the environment. The first forest surveys were made in the 1840s and provide a basis for comparison with modern times. From these sources, scientists have developed a good understanding of the environmental changes that humans have wrought. However, much of this understanding is still impressionistic and general, rather than quantitative and particular, and precise knowledge of the timing, rate and sequence of change must await more detailed regional studies (McGlone, 1989).
A large amount of information exists on the state of our land in more recent times, but much of this is several decades old, incomplete, scattered or poorly referenced. A comprehensive listing of the nation's main sources of land data is contained in the latest directory of environmental data published by Statistics New Zealand (1996a). Important sources include national soil and vegetation databases, which are largely compiled from field survey data collected by government departments decades ago, and more recent data from local authority monitoring programmes, national statistical series and scientific publications.
These latter sources include: land use statistics published annually in the New Zealand Official Yearbook, whose primary sources are Statistics New Zealand's two-yearly Agricultural Census combined with the Ministry of Forestry's survey-based estimates of timber production, planted forest area and new area plantings; and a variety of information held by local authorities, the Department of Conservation and Landcare Research on problems affecting particular ecosystems or areas. These supplementary data sources allow us to infer some local trends since the national databases were compiled but they cannot provide a full account of the state of the nation's land in the 1990s.
Surveys of soil and rock types were initiated in 1935 and 1940 respectively and took several decades to complete (New Zealand Soil Bureau, 1968). They provide the core data on which our soil and geological maps are based. Since then, other surveys and field studies have supplemented or revised some of this information, but, most of these are now also in need of revision. The soil and geology databases are held respectively by two Crown Research Institutes-Landcare Research and the Institute of Geological and Nuclear Sciences.
Probably the largest of Landcare's databases is the New Zealand Land Resource Inventory (NZLRI). This was developed in the 1970s by the Water and Soil Division of the Ministry of Works for the National Water and Soil Conservation Organisation (NWASCO, 1979). For five years, a small team of land resource scientists travelled over the country, recording details of land slope, soil erosion, soil type, rock type, and vegetation cover. The data were mapped and a land use capability assessment was made for the whole country (NWASCO, 1979). A number of NZLRI publications describing the land and land cover were produced in the 1980s (Crippen and Eyles, 1985; Lynn, 1985; Eyles, 1986; Hunter and Blaschke, 1986; Newsome, 1987).
Data on indigenous forest areas are based on two surveys by the New Zealand Forest Service: the National Forest Survey of 1945-1955; and the Ecological Survey of 1956-1967 (O'Leary, 1986). The area estimates from these surveys have been periodically revised since the early 1970s on the basis of timber production statistics. The current estimate of indigenous forest area (6.2 million hectares) has not changed since the early 1980s (New Zealand Forest Service, 1984). The NZLRI 1975-79 provides slightly lower estimates (around 5.9 million hectares), which vary according to assumptions made about the amount of forest contained within mapping units which include mixed vegetation.
Data on exotic forest areas are produced by the Ministry of Forestry, from a census of those growers known to have more than 40 hectares in exotic forest (Ministry of Forestry, 1994a, 1995). Recently, as the number of small plantations has increased, the Ministry has attempted to improve the information with satellite imagery (Pilaar et al., 1995). The Ministry has joined with Terralink NZ Ltd (formerly part of the Department of Survey and Land Information), the Department of Conservation, the Ministry of Agriculture, and Landcare Research, to develop a Land Cover Database based on satellite images. Funding is adequate to map the nation's forest cover, but additional funds are needed to include other types of land cover. As a result, non-forested land cover is only being added to the database in regions where local authorities are interested in purchasing the information. The database has 'fine grained data', each map unit being one hectare, but has only 15 land cover categories.
The NZLRI, by contrast, has many more vegetation and land cover classes, but has much coarser map units, seldom below 50 hectares, and often containing a diversity of land cover types. The purpose of the NZLRI map units is to depict areas according to their land use capability, regardless of their shape or size. Each map unit can, therefore, include a variety of vegetation types. A recent review by the Foundation for Research, Science and Technology recommended that the five layers of data in the NZLRI be separated into independent databases and updated and refined as necessary to accommodate the changes in erosion and land cover which have occurred in the last two decades. Landcare Research has now completed the second edition NZLRI mapping for Northland, Wellington, part of Marlborough and part of Waikato, and is currently remapping the Gisborne-East Coast region (Dymond, 1996; Stephens et al. 1995; Wilde, 1996).
Landcare Research has also recently initiated a national Biodiversity Assessment Programme which will begin with an assessment of our landscape and ecosystem diversity before proceeding onto species and genetic diversity. Landcare is also collating its other databases into a Spatial Database Index.
Terralink is a State Owned Enterprise (SOE) whose core businesses are mapping, surveying, property services, and collecting information and storing it on electronic databases. It provides data and services across the full range of administrative, cadastral, topographic, land cover, aerial photograph and satellite information types. These functions were previously carried out by the former Department of Survey and Land Information (DOSLI).
A variety of ecosystem databases are held by the Department of Conservation but their information tends to be descriptive rather than quantitive and they do not depict ongoing national trends, although some show short-term regional trends (e.g. Anderson et al., 1984). The databases include:
- a national dunelands inventory, which ranks dunelands of regional and national significance, based on surveys conducted in the 1980s by DSIR Botany Division (now Landcare Research) (Johnson, 1992; Partridge, 1992);
- the SSWI database (Sites of Special Wildlife Interest) which is a comprehensive listing of important wildlife habitat based on a nationwide survey by the former Wildlife Service's Fauna Survey Unit between 1977 and 1985, and updated for some regions and sites;
- a national weeds database; and
- an inventory of representative vegetation ecosystems from sites surveyed under the Department's Protected Natural Areas (PNA) Programme.
Although they are not national in their coverage, the monitoring programmes of regional councils are a rich, if uneven, source of data on soil, vegetation, and land use. For such data to be aggregated at the national level, the key indicators need to be measured in a standard way, using common methods and timeframes. The Ministry for the Environment (1996) is trying to develop such common methods for a selected core set of land indicators through the National Environmental Indicators Programme. The programme draws on expertise from Landcare Research, regional councils, and other agencies and organizations.