بازسازی انواع اکوسیستم کاج برگ بلند در زمین های خصوصی در جنوب ایالات متحده: تجزیه و تحلیل اقتصادی زیست محیطی

The longleaf pine ecosystem is one of the most biologically diverse in North America, supporting hundreds of plant and animal species. Because of its timber and many non-timber benefits, there is strong interest among forestry professionals, conservation groups, and the public at large in restoring longleaf pine ecosystems. However, many landowners are reluctant to grow longleaf pine on their lands on a commercial basis because the economic returns from longleaf pine timber production are usually less than those of slash pine. In this study, we develop a model that determines the profitability of longleaf and slash pine timber production after consideration of carbon sequestration, habitat for the endangered red-cockaded woodpecker, and other amenity benefits. Results suggest that internalizing carbon sequestration benefits and red-cockaded woodpecker habitat benefits alone is not enough for landowners to switch from slash pine to longleaf. Additional payments of $16 to 33 per ha per year, reflecting extra amenity benefits associated with longleaf pine relative to slash pine, make longleaf production financially competitive. Incentives that reflect carbon, biodiversity, and amenity benefits associated with longleaf production may be the optimal way of restoring longleaf pine ecosystems on rural private lands in the US South.

1.1. Longleaf pine The longleaf pine (Pinus palustris) ecosystem was once the predominant forest community in the southeastern coastal plain of the United States (US) before European settlement, covering over 36 million ha ( Lander et al., 1995). At present, less than 1.2 million ha of longleaf pine remain since most mature longleaf stands are not being adequately regenerated after harvest ( Delly and Gechtold, 1990). Humans have had a significant impact on this ecosystem for several hundred years. During colonial times longleaf pine was harvested mostly for its valuable wood. However, largescale logging of longleaf pine forests occurred in the 19th and early 20th centuries. Longleaf pine forests were further reduced during the 1950s when timber and pulp and paper industries started to use faster growing loblolly pine (Pinus taeda) and slash pine (Pinus elliottii) on land that used to support longleaf pine. Lack of reforestation and government policies that encouraged the exclusion of fire also contributed to the decline of longleaf pine. Finally, the conversion of cut-over lands to agricultural use led to further reductions in longleaf pine forests in the US South. Today, virgin longleaf stands exist only in a few isolated areas ( Abrahamson and Hartnett, 1990). Longleaf pine ecosystems are rich in biodiversity, supporting hundreds of plant and animal species. The dramatic decline of this ecosystem has had significant negative environmental consequences—over 30 plant and animal species that occur in this ecosystem are now threatened or endangered (Lander et al., 1995). The most notable example is the red-cockaded woodpecker (RCW, Picoides borealis), which was listed as endangered in 1970. The RCW needs mature pine, preferably longleaf pine at least 25 years old for foraging habitat, and at least 60 years of age for nesting habitat ( Wood and Kleinhofs, 1995). Because of its wide range and the high proportion of forest land in private ownership in the southeastern US, restoration on private lands is essential for the recovery of the RCW. One of the consequences of replacing old growth longleaf pine with alternative fast growing tree crops, agricultural crops, and urban development is significant changes in the amount of carbon stored in forest biomass. With public concerns over the rapid rise in CO2 levels, this represents the loss of a significant environmental benefit. In addition to environmental benefits, longleaf forests have unique characteristics that may translate into potential economic benefits to landowners. First, longleaf is much more resistant to fire than other commercial timber species such as loblolly or slash pine. In fact, regular occurrence of low intensity ground fires reduces competition from other plants and improves the biodiversity in the herbaceous ground cover (Dennington and Farrar, 1983). Second, it is more resistant to fusiform rust and bark beetle attacks than other pine species. 1.2. Challenges to restoring longleaf pine on private lands Because of the above environmental and economic benefits associated with longleaf pine, there is a strong interest among forestry professionals and conservation groups in restoring this ecosystem. For instance, in Geneva County, AL, over 2000 ha of marginal agricultural land were planted with longleaf pine through the Conservation Reserve Program. The Florida Division of Forestry has made it a top priority to restore longleaf pine on state forest lands. Non-governmental organizations such as The Longleaf Alliance and many government organizations including the USDA Forest Service have been providing forums to exchange information and conduct research on various issues related to longleaf pine restoration. Although they prefer to see longleaf, many landowners are reluctant to grow longleaf pine on their land on a commercial basis. The main reason for this is that the economic returns from longleaf pine are generally less than those of loblolly or slash pine.1 However, these returns do not account for environmental benefits such as carbon sequestration and biodiversity. In the absence of established markets for these services, private forest landowners generally perceive them as public goods and do not consider them in their land-use decisions. However, developing markets for these services may increase economic returns, thereby stimulating landowners to restore longleaf pine on their land. If environmental benefits are internalized, it is quite possible that longleaf pine may become financially competitive with slash and loblolly pine. In the absence of such information, initiating policy development to promote longleaf pine on private lands is difficult. This study is aimed at exploring economic strategies to restore longleaf in the US South. The specific objectives are: 1 Develop an economic model that incorporates timber and carbon sequestration benefits associated with longleaf pine and slash pine. 2 Estimate rotation age, land values, and the amount of carbon stored under longleaf and slash pine production. 3 Compare land values under longleaf pine after considering extra amenity benefits relative to slash pine. 1.3. Rationale to include carbon sequestration benefits There is a growing concern over the accumulation of ‘greenhouse gases’, particularly carbon dioxide (CO2), and associated global warming. In 1997, over 160 nations gathered in Kyoto to discuss strategies to limit greenhouse gas emissions and agreed to take steps toward achieving the stabilization of greenhouse gases in the atmosphere at a level that will prevent dangerous anthropogenic interference with the climate system (IGBP, 1998). Article 3.3 and 3.4 of the Kyoto Protocol recognizes that forests play an important role in the global carbon cycle through the conservation of existing carbon pools, through sequestration of carbon in new forests, through substitution of forest products for more energy-intensive materials, and through substitution of biomass fuels for fossil fuels (Brand, 1998). Furthermore, preliminary research indicates that carbon sequestration through forestry practices can be cost effective. Sedjo et al. (1995) noted that by creating plantations, carbon can be sequestered or conserved at less than $5 per ton. Dixon (1997) estimated that sequestration of carbon through silvicultural practices could cost between $2 and 56 per ton. Furthermore, if the life span of forest products is extended through recycling and fossil fuel displacement is achieved, the carbon balance may never be negative with timber harvest. In this study we assume that public agencies will provide payments for net CO2 assimilation and tax net CO2 emissions, thereby generating a cash flow of positive net payments from regeneration to harvest followed by negative net payments at harvest from biomass decay (Hoen and Solberg, 1997). Internalizing the public benefits of forest carbon sequestration through subsidies and taxes should have significant impacts on forest management. van Kooten et al. (1995) and Hoen and Solberg (1997) found that inclusion of carbon benefits causes an increase in rotation age. Stainback and Alavalapati (1999) found that forest land values will increase by considering carbon benefits. More recently, Enzinger and Jeff (2000) found similar results for eucalyptus (Eucalyptus globulus) in Australia. Our approach of incorporating carbon benefits is similar to the above studies. First, we estimate the effect of carbon taxes and subsidies on rotation age, land values and carbon supply for longleaf and slash pine plantations. Our model determines sawtimber and pulpwood composition endogenously as a function of age. Since carbon values are expected to have a positive impact on the rotation age, sawtimber proportions increase. Following Hoen and Solberg (1997), we also include decay functions and assume that sawtimber and pulpwood totally decay in 100 and 5 years, respectively. The decay rates are assumed to be linear over these periods. This implies that if we produce 1 m3 of sawtimber today, 1/100 of that quantity will decay each year, and by the end of 100th year there will be no biomass left in the form of sawtimber. We realize that a uniform decay rate may not be very realistic, however, in the absence of information about decay rates, we believe that a uniform decay rate assumption is justified. RCW prefer older pine stands, particularly longleaf pine stands. In our model a landowner is paid for producing RCW habitat. The amount paid increases with stand age, with benefits being small for young stands (i.e. stands younger than 30 years) but increasing to a plateau when the stand reaches approximately 60 years in age.

4.1. Forest management implications Many consider global warming to be the most important global environmental problem. The US, which contributes approximately 25% of the world's greenhouse gas emissions, will necessarily be a major part of the solution. As discussed above, carbon sequestration by forests offers the potential to reduce the cost of addressing global warming. Since the US South is the nation's ‘wood basket’, any policy to sequester carbon in forests is likely to have a significant impact on the region. In addition, issues such as biodiversity conservation, aesthetics, and urban sprawl are becoming increasingly important regional environmental concerns. Since the vast majority of forest land in the US South is privately owned, these issues will need to be addressed through private forest management. We find that a carbon subsidy and tax policy increases the optimal rotation age for both slash and longleaf pine, and internalizing RCW habitat benefits increases LEV for longleaf pine, but has a very small impact on the optimal rotation age. The greater value of private forest land could entice landowners to put a larger portion of their land into forest production thereby increasing the timber supply at the extensive margin. This increase in the value of forestland could also reduce forest conversion to other uses such as urban development. This could be a benefit in the southeastern US where many view urban sprawl as a significant concern. From the landowners perspective, longleaf pine is still not competitive on most sites with slash pine when carbon and RCW habitat benefits are internalized. However, with an additional subsidy to reflect other benefits of longleaf pine, in the range of $16–33 per ha per year, longleaf pine does become financially competitive with slash pine. Thus a carbon subsidy and tax along with a longleaf subsidy could significantly alter forest management in Florida and induce landowners to plant more longleaf pine. The amount of carbon sequestered is greater in longleaf pine than slash pine across the moderate to high range of carbon values analyzed. This trend is indicative that the amount of carbon sequestered from forestry activities is dependent on the growth rate of the stand, rotation length used, and the end products produced from the stand. 4.2. Study limitations and future research There are several limitations to this study. First, rotation age is only one input in the production of forest products. We did not address other changes in forest management that could result from a carbon subsidy and tax policy. For instance, carbon taxes and subsidies would probably have an impact on the amount of fertilizer, pesticides, and stocking density used by landowners. These factors would not only affect the amount of carbon sequestered but other environmental aspects of forestry as well. Second, as mentioned before, there is substantial uncertainty associated with the value of longleaf pine as RCW habitat on a per hectare basis. A significant increase in the value of RCW habitat would favor longer rotations and longleaf instead of slash pine. Finally, the change in timber supply caused by changes in the optimal rotation age and LEV will inevitably influence the market price of sawtimber and pulpwood. This price change will in turn influence forest management decisions. To more accurately predict the impact of a carbon subsidy and tax policy, price changes resulting from this policy would need to be considered in the model. This study can be extended in several possible ways in the future. First, the model could be extended by including thinnings and other non-timber products such as pine straw. Second, biomass from harvest could be sold and utilized for biofuel production. Inclusion of biofuel in the analysis could significantly affect the carbon benefits associated with forestry. Finally, there could be other socioeconomic and institutional factors, such as lack of information, uncertainty and other forest management objectives, which may limit the planting of longleaf pine. Exploration of these issues may help formulate future policies.