An estimate of carbon stocks for harvested wood products from logs exported from New Zealand to China

Abstract

In 2015 New Zealand exported 10.5 Mm3 of logs to China. A model has been developed to quantify the carbon stocks of harvested wood products (HWP) manufactured in China from these logs and the life cycle of the HWP produced. The model allows the aggregate decay curve of the HWP carbon stock to be estimated together with the 95% confidence interval. Overall, the HWP produced in China from New Zealand logs are short-lived with an aggregate half-life of just under two years. Some 46% of the HWP is lumber and plywood used for temporary construction while 13% is used for packaging which is also short-lived. There is a long tail in the carbon decay curve with 10% of HWP still in use after 23 years. Longer lived products are the 9% of HWP used for appearance products including furniture as well as panel products produced from a proportion of sawmill and plymill residues.Logs have been exported to China annually since 1987 and at levels exceeding 5 Mm3/year since 2010. The total HWP carbon stock from historical log exports is estimated to be 22.7 Mt CO2 at the end of 2015 with a 95% confidence interval of 19.1–26.4 Mt CO2. The annual increase for 2015 is estimated to be 1.9 ± 0.5 Mt CO2.The model developed will support New Zealand in meeting UNFCCC carbon reporting and Kyoto Protocol carbon accounting requirements. The analysis highlighted the importance of certain model inputs on which future effort should be focused.