Carbon Dioxide Emissions and Sinks From Forest Management
and Land-Use Change
Overview
Carbon cycles through the forest ecosystem in Rhode Island in significant
quantities. Because forest
ecosystems are a large store of carbon, relatively small percentage changes in
the amount of carbon stored in forests potentially could affect the overall
inventory significantly. Natural
forces and changes in land use on forests cause the amount of carbon stored in
forests to change over time. This
can result in a net uptake or net emission of carbon to the atmosphere.
Carbon emissions from changes in the area of forested land accounted
for 0.8% of all greenhouse gas emissions in 1996.
The total amount of carbon that was lost from the forests to the
atmosphere annually was 26,379
MTCE. The estimation method used
gives an annual average for the years between 1985 and 1998, the inventory
necessarily shows the same emissions for 1990 and 1996.
Methods
The methodology used to estimate the carbon emissions from forest
management and land use change came from State
Workbook: Methodologies for Estimating Greenhouse Gas Emissions Volume VIII,
Chapter 6. The
most recent available data on the carbon stock in Rhode Island’s forests is
for the years 1985 and 1998, from Forest Statistics for Rhode Island,
compiled by the U.S.D.A. (The
1998 statistics are from a draft report, kindly provided by the Division of
Forest Resources, RIDEM.) The
amount of carbon stored in the forests was estimated as a function of forest
biomass, and of land area. The
total difference between these two years was used to estimate the average yearly
carbon flux. The detailed data
and calculations used to estimate this flux are reported in Appendix
D.
Results
The annual average change in carbon stored in the forest shows a net decrease
in carbon stored in Rhode Island’s forests between the 1985 and the 1998
inventory years, mainly due to the decrease in land area classified as
forested. Over this time period, approx. 5% of Rhode Island’s forested land
was converted to other land uses, with an average annual loss of forested land
of 1.45K acres. [The Costs of
Suburban Sprawl and Urban Decay in Rhode Island, published in February,
2000 determined the change in forested area from RIGIS data, and found an
average annual loss from 1988 to 1995 of 1.43K acres.
However, the total forested area reported in the Sprawl study
is 300K acres for 1995, compared to 393K acres estimated by the Forest
Service. Since the calculation of
carbon flux depends on the change in acreage, not the absolute amount, this
total area disagreement does not affect our calculations.] The amount of
carbon stored in the forest
understory, the soils, and the
forest floor
is
calculated directly from the area of forested land.
Despite the decrease in this area, the amount of carbon stored in trees
increased because of an increase in the biomass density of Rhode Island’s
forest, thus partially offsetting decreased sequestration in forest soils.
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Average
Flux of Carbon Per Year from Forested Land
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Uncertainty
The data on which the amount of carbon sequestered in forest wood and
forest soils are for only two years, and the method of calculation assumes
that the changes are the same for each intervening year.
Of course, that is very unlikely to be the case.
Lacking Rhode Island-specific data on soil carbon, the Workbook factors
were used to estimate the amount of carbon in soils. Also, this survey does not take into account the final
destination of wood taken from the forest.
When logging thins a forest, there is an opportunity for carbon
sequestration due to the re-growth of trees.
If the wood that is taken from the forest is stored (e.g. used in the
construction of a house), this would represent a net uptake of carbon in the
forest system. However, if the
wood was burned as fuel, there would be no net sequestration. Data were not available to include these factors in the
inventory.
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