Data Collection and Estimation
In 2003, NEFD questionnaires were sent to all forest owners and managers with at least 40 hectares of planted production forest. The major questions contained in this questionnaire are shown in Appendix 2.
Approximately 1400 questionnaires were mailed out. From this, 1262 responses were received, giving a response rate of 90 percent.
For questionnaires that were not returned and where owners had provided data in an earlier NEFD survey, this previously supplied information was re-used. The 2003 NEFD survey had 111 such cases. The total area represented by these owners was 11,859 hectares.
In addition to the data collected in the 2003 NEFD surveys, the results from a small grower survey conducted by Statistics New Zealand in 1995 have continued to be used in 2003. Details of this small grower survey are contained in A National Exotic Forest Description as at 1 April 1995. Work is currently underway to update these figures.
New planting not directly captured in the 2003 NEFD survey has been imputed.
Since 1992 the Ministry has conducted a new planting survey. This new planting survey measures the sale of planting stock from commercial forest nurseries. An estimate of national new planting is calculated form 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.
It has been recognised that the areas of new planting were substantially underestimated in the NEFD database prior to 1995.
In the 2003 NEFD database, adjustments have been made to the areas established between 1992 and 2002 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 database since 1995.
Table 2: Comparison of Total New Planting with New Planting Collected in Postal Surveys (hectares)
| align="center">Year of planting | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
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| 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 | 2001 | 2002 | |
| Total new planting1 | 50 200 | 61 600 | 98 200 | 73 900 | 83 600 | 63 700 | 51 200 | 40 000 | 33 600 | 30 100 | 22 100 |
| New planting collected in postal surveys2 | 29 500 | 38 700 | 53 800 | 48 700 | 53 700 | 38 600 | 32 600 | 23 500 | 20 700 | 13 800 | 13 200 |
| New planting adjustments3 | 20 700 | 22 900 | 44 400 | 25 200 | 29 900 | 25 100 | 18 600 | 16 500 | 12 900 | 16 300 | 8 900 |
|
|
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Notes:
1. As estimated from the nursery
surveys undertaken by the Ministry of Forestry and the Ministry of Agriculture
and Forestry.
2. The area of planted forest as collected
in postal surveys excluding restocking. Any new information captured in
any subsequent year is deducted from the imputation in the appropriate year.
3. 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 12 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 1 to 5 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.
Contact for Enquiries
MAF Information Services
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PO Box 2526
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Fax: +64 4 894 0721
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