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It is necessary to estimate the area of afforestation and deforestation in New Zealand, since 1990, to meet reporting obligations under the Kyoto Protocol. We describe a method for national mapping of forest change that achieves high accuracy, but only requires moderate effort. A national coverage of satellite imagery is standardised, classified (automatically) for land cover, and then compared with an existing 1990 land-use map to identify polygons (>1 ha) of possible forest change. Each one of these possible change polygons is checked by operators for actual or spurious change. The resulting forest change map showed the area of afforestation between 1990 and 2008 was 579,000 (±10,000) ha, and the area of deforestation was 75,000 (± 5000) ha. This means that reported emission credits can never be reported to better than plus or minus 2%. Likewise, reported liabilities for emissions can never be reported to better than plus or minus 6%. |
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