Carbon is sequestered in products made from biomass. These products can be traded among nations, lowering the carbon stock of the exporting country and adding to the carbon stock of the importing country. When carbon is sequestered into biomass for specific climate mitigation options-such as wood for fuel or industrial purposes-a life cycle analysis is needed to describe the fate of the stored carbon. Improvement of life cycle assessment methods and comprehensive application of these assessment methods to case studies are important ways to judge the industrial side of the forest carbon cycle. Such analysis would include the conversion efficiency from tree growth into wood products.
Several waste products of wood processing (sawdust, wood chips, bark or lignin from cellulose production, etc.) decay and emit carbon, although such products can be further processed to produce boards or pulp-thereby increasing the efficiency of conversion (Hall et al., 1991)-or be used as energy sources. Wood products such as newsprint, fuel wood, paper, plywood, and sawn timber decay at rates that depend on the nature of their storage and use. Four life-span categories have been described for modeling carbon in forest products (Pussinen et al., 1997). Half of the short life-span products (fuel wood, newsprint, some packing paper, paperboard, and printing and writing paper) manufactured in 1 year were assumed to have not yet decayed after 4 years. The respective half-life-spans were 13 years for medium-short life-span products (the rest of packing paper, paperboard, and printing and writing paper), 30 years for medium-long life-span products (part of sawn timber and plywood), and 65 years for long life-span products (rest of sawn timber and plywood) products. Waste by-products can, however, be used as biomass to produce energy (see Section 1.4.4).
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