5 Reliability of Data
The New Zealand total area of planted forests in the 2005 NEFD database is estimated to be accurate to plus or minus 5 percent. That is, the New Zealand total net stocked forest area is estimated to be between 1.72 and 1.90 million hectares. The level of accuracy is reduced as the forest area is broken down into territorial authority and age class.
The data that make up the 2005 database have come from three sources as shown in Table 5.1.
NEFD Surveys
The data supplied by respondents to this survey are generally accurate and up-to-date. This reflects the commitment of the forest industry to having detailed forest resource information readily available. However, it is possible that some small-scale forest owners included in the database may change their management objectives. For example, areas currently intended to produce a harvestable timber yield may be left standing to provide shelter or for aesthetic appeal.
To minimise possible errors in the NEFD survey data, the following checks were made:
- Numerical data were limited to certain maximum and minimum values for each entry.
- Aggregated area data were checked at the territorial authority level against the 2004 NEFD area database to ensure variation was within acceptable limits.
Forest areas are sometimes mis-allocated between adjacent territorial authorities. One way for users to minimise this problem is to aggregate data from adjacent territorial authorities, particularly where contiguous forest areas straddle territorial authority boundaries.
Table 5.1: Total Area Represented by Each Data Source in the 2005 NEFD Database
| Data source | Net stocked area (000 ha) |
Proportion of total area (%) |
|---|---|---|
| 2005 NEFD survey | 1 484 | 82 |
| 2004 AgriQuality small forest grower surveys 1 | 138 | 8 |
| New planting imputation (1992–2004) | 189 | 10 |
| Total | 1 811 | 100 |
Note
1. Small Forest Grower Survey Report, AgriQuality NZ, April 2005.
Imputed New Planting
The inclusion of the imputed new planting into the 2005 NEFD database makes the following assumptions:
- The new planting estimates from the nursery seedling surveys are the actual areas of new planting established between 1992 and 2004.
- The imputed new planting in each territorial authority occurs in the same proportion as the new planting captured in the 2005 NEFD survey.
- Imputed new planting for radiata pine is assigned to the tending regimes in the same proportions as the radiata pine new planting captured in the 2005 NEFD survey.
Yield Table Database
The radiata pine yield tables contained in the NEFD yield table database were revised during 1995–96, principally from data provided in 1995 by owners of extensive areas of forest. Data were collected from these owners because their holdings covered most districts in New Zealand, they made up much of the forest resource and they had the best yield tables databases in New Zealand.
For further details on the NEFD yield tables refer to NEFD Regional Yield Tables as at 1 April 1995.
A complete revision of the NEFD yield tables commenced in March 2005. It has taken longer than expected to collect up-to-date yield data from forest owners. Once all the data have been collected the new yield tables will be published. This is expected to occur in mid-2006.
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
Contact this person
