3 Data Collection and Estimation
In 2005, NEFD questionnaires were sent to all New Zealand forest owners and managers with at least 40 hectares of planted production forest. The major questions in this questionnaire are shown in Appendix 2.
Approximately 1340 questionnaires were mailed out. From this, 1165 responses were received, giving a response rate of 87 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 2005 NEFD survey had 175 such cases. The total area represented by these owners was 30 877 hectares.
In addition to the data collected in the 2005 NEFD survey, the results from the recently completed AgriQuality New Zealand Small Forest Grower Surveys have continued to be used in the 2005 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 2005 NEFD survey has been imputed.
New Planting Imputation
Since 1992 MAF 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 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).
In the 2005 NEFD database, adjustments have been made to the areas established between 1992 and 2004 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.
The national new planting adjustments were distributed into territorial authorities using the proportions indicated from the new planting collected in the postal survey. Table 10.7 shows how the adjustments for recent new planting have been distributed across territorial authorities.
Table 3.1: Comparison of Total New Planting with New Planting Collected in Postal Surveys
| Calendar year of planting (ha) | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 | 2001 | 2002 | 2003 | 2004 | |
| 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 | 19 900 | 10 600 |
| New planting collected in postal surveys2 |
29 700 | 39 800 | 69 600 | 68 600 | 65 500 | 45 600 | 36 800 | 26 800 | 25 300 | 18 700 | 15 200 | 11 800 | 5 800 |
| New planting adjustments3 | 20 500 | 21 800 | 28 600 | 15 300 | 18 100 | 18 100 | 14 400 | 13 200 | 8 300 | 11 400 | 5 900 | 8 100 | 4 800 |
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.
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.
Contact for Enquiries
MAF Information Services
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PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
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