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1.4.3. The Fate of Stored Carbon in Biomass Products
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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