Quantifying the carbon in NZ log exports

In 2015, New Zealand exported 15.4 million m 3 of logs, some 53% of the national harvest, with 96% going to China, South Korea and India. Models have been developed to quantify the harvested wood products (HWP) manufactured in each country from these logs and the lifecycle of the HWP produced. The model allows the decay curve of the HWP carbon stock to be estimated.

Carbon stocks in the products manufactured in China from New Zealand logs are halved in just under two years. Some 46% of the HWP is lumber and plywood used for temporary construction, while 13% is lumber and plywood used for packaging, which is also short-lived.

In South Korea, the carbon stocks are halved in just over 12 years. Although the 42% of material used for temporary construction has a short-life in that intermediate use, most is recycled into longer-lived particleboard. In addition, 30% of log volume (mainly sawmill slabwood and plymill residues) is used for the production of medium-density fibreboard (MDF), another long-lived panel product.

In India, the overall carbon stocks are halved in less than one year. Some 26% of the radiata pine log volume is directly used for fuel, including slabwood (14%) and most sawdust (12%), while construction lumber (27%) is also used for fuel after use for concrete formwork. Packaging material (31%) is also short-lived, particularly domestic packaging.

In combination, the aggregate decay curve for the three countries has carbon stocks halved in just over two years. These findings have implications for New Zealand's carbon accounting under the Kyoto Protocol and carbon reporting under the United Nations Framework Convention on Climate Change (UNFCCC). If the deferred liability for emissions from HWP is devolved to forest growers participating in the New Zealand Emissions Trading Scheme (NZ ETS), the decay rate adopted for HWP will have a major impact on the carbon stock profile over time for a tree crop, and hence forest profitability and risk and, consequently, the financial viability of afforestation.

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Source: New Zealand Journal of Forestry November 2017

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