A National Exotic Forest Description (2007) – NEFD
3 Data collection and estimation
In 2007, NEFD questionnaires were sent to approximately 90 forest owners and managers who owned more than 1000 hectares of planted production forest. The questionnaire used is shown in Appendix 2. A 99 percent response rate to the survey was achieved.
For forest owners with less than 1000 hectares, the data collected in the comprehensive 2005 NEFD survey continues to be used in the 2007 database. An issue with this is that a small area of mature forest from the 2005 database will have been harvested between 2005 and 2007. This will lead to a small amount of overstatement of the area in the older age classes. Conversely, areas restocked post-harvesting between 2005 and 2007 by owners with less than 1000 hectares will be understated in the 2007 NEFD database.
For details of the 2005 NEFD survey, refer to A National Exotic Forest Description as at 1 April 2005.
In addition to the data collected in the 2005, 2006 and 2007 NEFD surveys, the results from the 2004 AgriQuality (now AsureQuality) Small Grower Surveys continue to be used in the 2007 database. Details on the methods used by AgriQuality are available in the Small Forest Grower Survey Report (AgriQuality NZ, 2005).
New planting not directly captured in the 2007 NEFD survey has been imputed based on the results of the 2007 new planting (nursery) survey.
New planting imputation
Since 1992, MAF has conducted a new planting (nursery) survey. This new planting survey measures the sale of planting stock from commercial forest nurseries. An estimate of national new planting is calculated from the numbers of seedlings sold. Details of how this survey is operated are described in Predicting and Measuring New Planting from Nursery Surveys (Eyre, 1995). This new planting survey provides the most complete indicator of the area of new forest established each year. The methodology was reviewed in 2003 (Manley et al, 2003).
It has been recognised that the areas of new planting were substantially underestimated in the NEFD databases prior to 1995.
In the 2007 NEFD database, adjustments have been made to the areas established between 1992 and 2006 to account for the areas of new planting not collected in the postal surveys. This same method of imputation has been used in the compilation of the NEFD databases since 1995. Table 3.1 shows the comparisons of new planting figures collected in the postal surveys to the total new planting figures.
Table 3.1: Comparison of total new planting with new planting collected in postal surveys
| Calendar year of planting (ha) |
Total new planting1 |
New planting collected in postal surveys2 |
New planting adjustments3 |
|---|---|---|---|
| 1992 | 50 200 | 30 900 | 19 300 |
| 1993 | 61 600 | 40 400 | 21 200 |
| 1994 | 98 200 | 68 400 | 29 800 |
| 1995 | 73 900 | 56 200 | 17 700 |
| 1996 | 83 600 | 64 600 | 19 000 |
| 1997 | 63 700 | 45 600 | 18 100 |
| 1998 | 51 200 | 36 300 | 14 900 |
| 1999 | 40 000 | 23 700 | 16 300 |
| 2000 | 33 600 | 24 700 | 8 900 |
| 2001 | 30 100 | 17 100 | 13 000 |
| 2002 | 22 100 | 14 300 | 7 800 |
| 2003 | 19 900 | 11 800 | 8 100 |
| 2004 | 10 600 | 6 200 | 4 400 |
| 2005 | 6 000 | 2 900 | 3 100 |
| 2006 | 2 600 | 1 500 | 1 100 |
Notes
- As estimated from the nursery surveys undertaken by the Ministry of Forestry and the Ministry of Agriculture and Forestry.
- The area of new planting as collected in postal surveys. This does not include the area of restocking.
- The difference between total new planting and new planting collected in postal surveys.
The national new planting adjustments were distributed into territorial authorities using the proportions indicated from the new planting collected in the postal survey.
Table 9.7 shows how the adjustments for recent new planting have been distributed across territorial authorities.
Within each territorial authority the imputed new planting was allocated to NEFD crop types using the postal survey results in the following way:
- The imputed new planting was allocated into species groups based on the relative proportions of each species group within the one to five year age class.
- For radiata pine, the imputed new planting was allocated into the four NEFD tending regimes, based on the relative proportion of each of these tending regimes across all the age classes. All the Douglas-fir imputed new planting was allocated to the “without production thinning” tending regime.
Historically imputed new planting estimates are revised each year, based on any new information on the area of young forest captured directly in the NEFD survey.
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