Modeling the effects of forest management on the carbon cycle in a loblolly pine (Pinus taeda) plantation
Spinney, Michael Paul
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Forests have the ability to alleviate the impact of global warming through carbon sequestration. Six forest management scenarios for a 27,000 acre study area are modeled to determine the impact of forest management on carbon sequestration. Forest management determines annual harvested volume and end-use disposition category of wood products, and inventory volume. Shorter rotations tend to produce short-lived wood products, while longer rotations produce long-lived wood products. Thinning removes pulpwood, which increases the average diameter of the stand and increases the proportion of sawtimber products. Changing forest management complicates accounting for changes in future C storage. Understanding the distinction between pre- and post-regulation harvest volume and C storage is essential to understand the effects of forest regulation. Plotting harvested volume and C storage volume over time shows distinctive pre- and post-regulation characteristics. The pre-regulation curves exhibit irregularities and varying thinned volume due to the uneven area in the existing age classes. Post-regulation curves are level because a constant area is annually thinned and clearcut. Carbon storage is the amount of C that is sequestered into a C pool, which for the purposes of this study is either inventory volume or residual wood product volume. Converting volume flows to C storage involves tracking the accumulation of wood products and standing volume over time then converting volume to a measure of C. Once the forest is regulated, C stored in the inventory pool remains constant from year to year, while the C stored in wood products continually increases. Longer rotations store more carbon than shorter rotations because they have larger inventory pools. Wood products are a substantial carbon pool: at the end of 50 years; the ratio of incremental C in the wood products carbon pool to incremental C in the inventory pool ranges from 6 to 122 for the modeled scenarios. Three accounting periods are evaluated to examine the importance of C sequestration timing to determine if a market for C can influence forest management. Long rotations meet the objectives of maximizing C sequestration and NPV for the modeled regimes regardless of the accounting period considered, or if the forest is regulated or un-regulated. Model sensitivity to decomposition rate, discount rate and timber prices is assessed to determine the effects of uncertainty (measurement error and future trends) on the results of the model. Short rotations are most sensitive to decomposition assumptions and stumpage prices because they produce a large amount of fast-decaying wood products. Long rotations are most affected by discount rate. Carbon storage of all scenarios increases substantially when the pulpwood decomposition rate equals the sawtimber decomposition rate to reflect a potential future increase in composite lumber production.
- Masters Theses