تجزیه و تحلیل اقتصادی از جداسازی کربن در جنوب ایالات متحده از جنگل های کاج بریده

The impact of a carbon subsidy and tax policy on slash pine (Pinus elliottii) plantations is investigated using a modified Hartman model. Such a policy is shown to increase the optimal rotation age, land expectation value and the supply of sequestered carbon. The supply of carbon increases at a decreasing rate with the price of carbon. The supply of sawtimber increases while the supply of pulpwood decreases. The increase in land expectation value was substantial, suggesting inclusion of carbon sequestration benefits and emission costs would benefit private forestland owners. As the value of forestland increases in response to a carbon policy, more land could be devoted to forestry as opposed to other land uses such as agriculture and urban development.

There is growing concern over the accumulation of “greenhouse gasses”, particularly carbon dioxide (CO2), and associated global warming. As a result of global warming, sea levels may rise causing inundation of some coastal areas and the earth’s environment may be altered affecting biodiversity and food security in many regions. Since the early 1990s, governmental and non-governmental organizations across the globe have been discussing strategies to mitigate atmospheric concentrations of greenhouse gasses (Hedger 1998). In 1997 the United Nations Convention on Climate Change adopted the Kyoto Protocol requiring industrialized countries to reduce their greenhouse gas emissions to approximately 5% below 1990 levels by 2008–2012. The details of the Protocol were worked out in November 2001 in Marrakesh, Morocco and it appears likely that it will enter intoforce in the next couple of years. The current U. S. administration, however, has opted out of the Kyoto Protocol and has developed an alternative that it claims would be less harmful to the U. S. economy. It is widely recognized that forests play an important role in the global carbon cycle by sequestering and storing carbon, enabling the switch from more energyintensive materials such as steel to forest products, and facilitating substitution of biomass fuels for fossil fuels (Brand 1998). It is this role of forests in climate change that has influenced participants of the Kyoto Protocol to allow countries to count carbon sequestered in forest to be counted toward a country’s emission requirements. As the U. S. has long been a proponent of this idea, the Bush administration has proposed over 3 billion dollars in its alternative climate change proposal for forestry and agricultural carbon sequestration activities (Bush 2002). Preliminary research indicates that carbon sequestration through forestry practices can be cost effective. For example, Dixon (1997) estimated that sequestration of carbon through silvicultural practices could cost between $ 2–56 per metric ton. Current projections by the Resources Planning Act assessment models show that through the year 2040 about 15 percent of projected U. S. carbon emissions will be sequestered by forests (Murray et al. 2000). These projections are based on current management trends such as decreased logging in the Pacific Northwest. Carbon sequestration varies depending upon the nature of forests. Old growth forests are expected to have large stocks of carbon with limited potential for carbon sequestration since net biomass growth is negligible.A young forest, on the other hand, will have low stocks of carbon but large carbon uptake due to rapid growth of young trees. Some researchers have noted that harvest of old growth forests would result in a net flux of carbon to the atmosphere that would take hundreds of years before recovering the original net carbon stored (Harman 1990). This has provided a rationale to be cautious about the harvest of old growth forests from a climate change perspective. However, forests already under management for commodity production could sequester additional carbon by lengthening the rotation and producing more products with a long product life such as sawtimber as opposed to products with a shorter product life such as pulpwood. There is a problem, however, in capitalizing on the comparative advantage of producing an additional amount of timber and associated carbon. In the absence of markets for forest carbon, private timber producers consider carbon external to their production decisions. As a result, forest biomass production and associated carbon sequestration may be lower than is socially desirable. In the case of public lands, this problem can be resolved by manipulating government budget allocations. However, in the case of private lands, incentives may be necessary to stimulate landowners to consider carbon sequestration benefits in their production decisions (Alavalapati 1998).Consider forestry as a cycle of biomass production with net CO2 assimilation and biomass decay with net CO2 emission. If subsidies are given for net CO2 assimilation and taxes are imposed on net CO2 emission, this will generate a cash flow of positive net payments from regeneration to harvest followed by negative net payments following harvest because of carbon emissions (Hoen and Solberg 1997). If reforestation, afforestation, and the use of forest products can generate a net positive carbon balance, net subsidies may be justified for forest carbon sequestration.

Internalizing forest carbon sequestration benefits would have a significant impact on the management decisions of private forestland owners.Positive values for carbon cause a significant increase in forestland values. This increase in privateforestland values could entice landowners to put a larger portion of their land into timber production, thereby increasing timber supply at the extensive margin.Typical LEVs in the southern U. S. range from approximately $ 1000 per hectare to $ 3500 per hectare (Hite et al. 1999).The increase in the value of forestland could also reduce forest conversion to other uses such as urban development. Since urban sprawl and forest fragmentation is an increasing concern in many parts of the southern U. S., increasing the profitability of forestry through carbon sequestration policies would influence landowners to continue forestry practices or even divert other lands to timber production.This may be a cost effective approach of improving the environment by limiting greenhouse gases in the atmosphere and conserving rural lands. The increase in land values also has implications for the implementation of a carbon subsidy and tax policy. The fact that landowners would gain substantially from such a policy indicates that it could be implemented on a voluntary basis similar to the way the Conservation Reserve Program (CRP) is currently implemented. In the CRP, farmers are paid yearly subsidies for 10 years for taking environmentally sensitive farmland out of production or planting trees. With a carbon subsidy and tax policy, landowners could opt to receive yearly subsidies for sequestering carbon if they agree to be subject to carbon payments or taxes when the trees are harvested.A carbon market would encourage those who could sequester carbon the cheapest at the margin to enter the market. This may be a more efficient policy then one structured like the CRP that focused on sequestering carbon on the cheapest land (Parks and Hardie 1995). Stem wood volumes are routinely estimated to make forest management decisions so the necessary information to implement and monitor such a policy would be available. Even for the conservative carbon prices used in this study the increase in the supply of carbon offered by the landowner on the intensive margin increases at a decreasing rate. This implies that the marginal cost to supply carbon on the intensive margin rises relatively rapidly. Stavins (1999) used an econometric model to investigate the marginal cost of sequestering carbon by converting agricultural lands to forest in the U. S. and found that the marginal cost of sequestering carbon rises rapidly on the extensive margin for carbon prices above approximately $ 50 per metric ton.Thus even though forests are attractive in terms of sequestering carbon the marginal cost of sequestering carbon in U. S. forests would likely increase rapidly.Thus forestry will be one of many options needed for the U. S. to reduce net greenhouse gas emissions cost effectively (Stavins 1999). The change in sawtimber and pulpwood supplies could change prices for these commodities.The results from this research suggest that, on the intensive margin, sawtimber supply will increase and pulpwood supply will decrease. However if the increase in land area devoted to forest production brought about by the increase in forestland values is great enough both sawtimber and pulpwood supply could increase.A decrease in the price of sawtimber and an increase in the price of pulp-wood could dampen the effect of a carbon subsidy and tax policy by encouraging shorter rotations and more pulpwood production. Similarly a decrease in price for both sawtimber and pulpwood could dampen the impact of a carbon policy on the extensive margin. It should be pointed out that there are some limitations associated with this study. First, rotation age is only one of the many key factors in timber production. We did not address other changes in forest management that could result from a carbon subsidy and tax policy. For instance, it is probable that carbon taxes and subsidies would have an impact on the amount of fertilizer, pesticides and stocking density used by landowners. For example, carbon payments could induce landowners to increase their stocking density to capture more carbon benefits at the beginning of the rotation. On the other hand, the incentive to produce more sawtimber and have longer rotations would tend to decrease the optimal stocking density. In addition, as mentioned earlier, the change in timber supply caused by changes in the optimal rotation age and land values will inevitably influence the market price of sawtimber and pulpwood. These price changes will in turn influence forest management decisions. Therefore, in future studies it may be fruitful to consider prices as endogenous variables in the model specification. There are several additional ways to extend this study in the future. First, although the focus was on slash pine, the procedures can easily be extended to other species with different growth characteristics such as longleaf pine. In addition, there could be other socioeconomic and institutional factors, such as lack of information, uncertainty and other forest management objectives, which may limit landowners from undertaking forest carbon sequestration activities. Exploration of these issues in future studies may help formulate effective carbon policies in the southern U. S.