| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a USDA-Forest Service, Pacific Northwest Research Station, 3200 SW Jefferson Way, Corvallis, OR 97331
b CH2M Hill, 2485 Natomas Park Drive, Sacramento, CA 95833
* Corresponding author (ralig{at}fs.fed.us)
Received for publication April 29, 2005.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONHISTORICAL TRENDS IN FOREST...METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Abbreviations: EO, economic optimization • FASOM-GHG, Forest and Agricultural Sector Optimization Model-Green House Gas • GCC, global climate change • HB, historical behavior • MIC, management intensity class • NIPF, nonindustrial private forest
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONHISTORICAL TRENDS IN FOREST...METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Land use, land use change, and forestry have received increasing attention in GCC analyses over the last decade (e.g., Intergovernmental Panel on Climate Change, 2000). Experts in forestry, biology, ecology, economics, and related subjects have increasingly investigated human activities that alter land use and land cover. Factors that influence adaptation and the net terrestrial uptake of carbon include the direct effects of land use and land-use change (e.g., deforestation and agricultural abandonment and regrowth) and the response of terrestrial ecosystems to CO2 fertilization, nutrient deposition, climatic variation, and disturbance (e.g., timber harvest, fires, wind-throws, and major droughts). Direct mitigation strategies include reducing carbon emissions from forests by reducing the conversion of forests to farmland and other uses (i.e., reducing deforestation), setting aside existing forests from harvest, and reducing biomass burning. Other land-based strategies for increasing carbon buildup in forests are converting marginal agricultural land to forests (carbon plantations, forest product plantations, short-rotation woody crops, or joint product plantations), and enhancing forest management (e.g., Hoen and Solberg, 1994). Research findings can inform decision-makers about GCC adaptation and mitigation possibilities, while recognizing dynamic interactions among climate, ecological, and socioeconomic systems and attendant effects on agriculture, forestry, and natural resources.
Our integrated approach to analyzing the potential role of forestry in climate change mitigation strategies recognizes the major factors of biophysical–ecological, economic, and social influences on land management and investment behavior. The interface between ecological and economic factors involves a human ecology portion that includes physical patterns observed on a landscape. The economics portion involves consideration of financial returns and consumer demands, with distinction between private and social viewpoints, in that some effects are external to private producers' and consumers' outcomes. Social aspects in recognition of market failures or externalities can include government programs that can subsidize forest production to promote increases in standing timber stocks and forest carbon storage. Next, we look at historical trends in U.S. forest conditions because macro trends typically are not quickly reversed or substantially altered and provide useful information when contemplating intervening in ecosystems, markets, and social processes. Then, we describe our modeling methods, summarize projections for different forest investment scenarios, and discuss findings and point out policy implications and examples of future research needs.
|
HISTORICAL TRENDS IN FOREST CONDITIONS |
|---|
|
TOPABSTRACTINTRODUCTIONHISTORICAL TRENDS IN FOREST...METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
In the 1800s and early 1900s, deforestation was a source of CO2 emissions in the United States. However, by the 1950s, U.S. forests had become a sink, absorbing more CO2 through forest regrowth than was being lost through harvesting (Birdsey and Heath, 1995). With a projected U.S. population increase of more than 120 million people over the next 50 yr, more than 20 million ha of U.S. forest are projected to be developed (Alig et al., 2004). The United States would have less timberland area to support tree growth to sequester and store additional carbon, with a net reduction of about 6 million ha of timberland by 2050 (Alig et al., 2003).
To counter effects of deforestation, afforestation as a climate change mitigation option can potentially provide the most additional carbon sequestration in the United States over the next 10 to 30 yr (Birdsey et al., 2000). Government policies have influenced afforestation amounts, with periodic spikes in the amount of U.S. tree planting correlating with major government programs (Alig et al., 1980), including a spike in the latter half of the 1980s due to subsidized tree planting for environmental goals (e.g., reduced soil erosion). In the absence of such programs, projections by Kline et al. (2002) based on historical relationships indicate that the amount of tree planting in the U.S. South by the large nonindustrial private forest (NIPF) ownership class could decline in the future without cost-sharing or other subsidies.
However, other tree planting in reforestation of harvested forestland can encourage establishment of fast-growing species to foster more carbon storage in woody biomass (Hair et al., 1996). On a smaller land base, industry tree planting is projected to rise gradually with more timber harvest (Kline et al., 2002).
In most years timber harvest is the disturbance having the greatest effect on U.S. timberland and can lead to significant changes in land cover and forest carbon storage, shifting some carbon from forest ecosystems to wood product storage. Private timber harvests comprise more than 90% of the U.S. total. Projections based on "historical behavior" (HB) indicate that both timber harvest levels and standing timber stocks can increase in the future (Fig. 1) (Haynes, 2003). Implications for forest carbon storage are possible increases in the future as well, as Birdsey and Heath (1995) estimated that U.S. forests will continue to be net carbon sinks well into the future, sequestering carbon at an average net annual rate of 178 million Mg between 1992 and 2040 (not including sequestration into wood products and landfills), for a total increase in stored forest carbon of 8.5 billion Mg. Earlier "economic optimization" (EO) projections of forest investment indicated that expanded private forest investment relative to a HB baseline would allow some immediate increments in timber harvest, sustained increases in timber inventory, and virtually no long-term trend in softwood log prices (Alig et al., 1999a).
|
|
METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONHISTORICAL TRENDS IN FOREST...METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
FASOM models intertemporal optimizing behavior by economic agents. The decision to continue growing a timberland stand rather than harvesting it now is based on comparison of the net present value of timber harvests from future periods and any greenhouse gas offsets obtained (from not harvesting now) versus the net present value of harvesting now and either regenerating the land back to trees or shifting to agricultural use. Similarly, an afforestation decision would shift land out of agriculture if it had a greater net present value in forest use. This land-use optimization establishes a land price equilibrium across the two sectors and, given the land base interaction, a link between contemporaneous commodity prices in the two sectors as well.
The forest production component of FASOM-GHG depicts the use of existing private timberland as well as the reforestation decision on harvested land across the conterminous United States, broken into nine market regions (Fig. 2). Timberland is the subset of forestland that is capable of producing at least 0.23 m3 per ha per year of industrial wood at culmination of mean annual increment and is not withdrawn from timber harvesting or related timbering activities. Timberland is differentiated by region, the age cohort of trees (grouped in twenty-one 5-yr cohorts: 0 to 4 yr, 5 to 9 yr...up to 100+ yr; harvesting is assumed to occur at the midyear of the cohort), ownership class, cover type, site condition, management regime, and suitability of the land for agricultural use. Decisions pertaining to timber management investment are endogenous. Actions on the timber inventory are depicted in a framework that allows timberland owners to institute management activities that alter their inventory to maximize net present value of the economic returns from the activities. Decisions for existing stands include selecting the harvest age. Lands that are harvested and subsequently reforested or lands that are converted from agriculture to forestry (afforested) introduce decisions involving the choice of species type, management type, and future harvest age.
|
An important aspect of the MIC is the associated costs. Included in the FASOM-GHG model are conversion, establishment, and forest management costs for each specified MIC (Bair and Alig, 2006). Forest establishment costs include those for site preparation, tree seedlings, and tree planting. Intermediate timber management costs include those for precommercial thinning, prescribed burning, fertilization, and any other practices between stand establishment and harvest. Establishment costs vary by FASOM-GHG land class, with generally higher costs for reforested hectares than for afforested hectares.
To estimate the impact of biological and financial changes to timberland inventories and harvest levels, we modeled alternative policy scenarios that create incentives and disincentives for timberland investment. These scenarios include sensitivity analyses involving forest management costs and timber yields. Restriction and expansion of high intensity timberland management is also modeled in the FASOM-GHG scenarios.
Our first set of scenarios (Scenario Set A) involves changes in costs of forest establishment and forest management for both existing and regenerated stands, testing both 50% reductions (Scenario A1) and increases (Scenario A2) compared to the baseline. The reduction is in line with cost sharing as a policy that provides incentives for timberland investment. Most state and federal tree planting programs provide approximately 50% of the incurred cost of timberland establishment (Alig et al., 1990). This level of cost reduction is modeled and is held constant throughout the projection period. The assumption is made that timberland owners would take advantage of conservation easements, carbon credits, or technology assistance programs to reduce the intermediate and general management costs over the projection period by 50%. Conversely, we also increase timberland management costs by 50%. This increase in costs may occur if global climate change negatively influences precipitation and temperatures in timber producing regions, increasing the cost of establishment and management costs.
The next set of scenarios (Scenario Set B) involves changes in projected yield estimates for regenerated stands. Projected yield increases of 15% (Scenario B1) in FASOM-GHG compared to the baseline case represent the upper end of estimated gains from improved management and climate change favorable to timber production. Joyce and Nungesser (2000) state that improved management of timberland stands could increase yields 25 to 39%, while increased CO2 levels may increase yields by another 8 to 29%. However, changes in temperature and climate may reduce timberland yield in various locations. Considerable uncertainty exists about the influence that climate change may have on forest growth rates (Alig, 2003). Gains from increased management intensity would primarily occur on NIPF timberlands in the South Central and Southeast regions (Alig et al., 1999a), but for consistency are applied to all private owner groups across regions. The decreased yield scenario is the opposite of that for the assumed yield increase, with a reduction in yields by 15% (Scenario B2).
The last set of scenarios (Scenario Set C) involves assumed changes in forest investment that reflect intensity of forest management. The first scenario involves assuming increased forest investment (Scenario C1) to counter the projected baseline reduction in timber inventory in the latter half of the projection period. This equates to timber yield increases of approximately 35% for regenerated stands in the future. This emulates a relatively optimistic boost in timber yields, to help bracket the set of sensitivity analyses. At the other extreme, our relatively pessimistic scenario regarding reduced future forest investment involves elimination of tree planting (Scenario C2) when regeneration opportunities arise in the future, so that only natural regeneration and associated timber yields were employed after a stand was harvested.
In each of the aforementioned scenarios, standing timber volume is used as one indicator of forest carbon storage potential. This allows us to compare on a standing timber volume basis with the "historical behavior" case described earlier from the recent national timber assessment (Haynes, 2003), where the latter did not report forest carbon estimates and projects out 50 yr compared to 100 yr in this study. Significant differences in carbon storage can exist across forest types (Birdsey, 1992), and our preliminary projections from the updated FASOM-GHG model represent more forest types than the earlier 1990s model (McCarl et al., 2005).
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONHISTORICAL TRENDS IN FOREST...METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
The EO baseline projections extend out to 2100, in contrast to 2050 for HB, and show a 16% reduction in timber stocks from 2050 to 2100. The amount of national timber stocks is reduced in the latter half of the projection as proportionately more timberland is moved into plantations and other intensified forms of forest management. This would represent a transition to, on average, timber stands that are harvested at earlier ages than historical ones and with less volume per hectare. By 2100, the EO transformation of private timber stands results in a terminal amount of standing stock volume about 4% lower than the starting inventory in 2000.
Across the EO scenarios where costs (Scenario Set A) or timber yields (Scenario Set B) were altered by assumption, the scenario with the 15% increase in timber yields (Scenario B1) had the largest increases in both halves of the projection period relative to the baseline (Table 1, Fig. 3). However, even that scenario had an absolute volume decrease in the second half of the projection period, as the model effectively concentrates timber production on a smaller timberland base. To attain a projected timber volume trajectory that did not decline, enough forest investment (Scenario C1, "Increased Investment") would be needed to boost regenerated timber yields by approximately 35% (Table 1). Relative to the EO baseline, growing stock volume under the increased investment scenario (Scenario C1) moves notably upward after 2030 and by 2100 results in national timber stocks that are more than 25% larger than the base case (Fig. 3).
|
|
Intertemporal linkages between forest investment and timber harvest amounts, and attendant effects on amount of standing timber stocks, are evident in the scenario outcomes. For example, increasing the timber yields 15% in regenerated stands in the future (Scenario B1), compared to the EO baseline, decreases the inventory before 2025 below baseline projections. Because of perfect foresight, the model can improve the total financial return for landowners by harvesting earlier in the projection period, in anticipation of higher growing stock inventory levels later due to increased investment.
Conversely, in FASOM-GHG, decreasing the timber yields for regenerated stands (Scenario B2) increases the volume of private standing timber relative to EO baseline projections until the period 2030, and then they drop below the baseline level. In this case, the model's foresight anticipates higher timber prices in the future with less standing timber inventory, and postpones some timber harvest until then.
This timing effect is more pronounced in the restricted investment scenario (Scenario C2), with standing timber volumes notably higher than under all alternative EO scenarios before 2045 (Fig. 3). However, timber growing stock under the restricted investment scenario then drops and diverges over time from the EO baseline. In addition, cumulative timber harvest levels over the entire projection period are materially lower than the EO baseline scenario (Table 1).
Although previous studies investigating the link between climate change and the forest sector have focused on various economic and biological impacts of global climate change, there are some common themes. One earlier finding that is consistent with the FASOM-GHG model is that timber yield increases result in higher standing timber volumes. Alig et al. (2002) and Perez-Garcia et al. (2002) find that increasing timber yields increases standing timber volume over 100-and 40-yr projections, respectively.
Projected outcomes pertaining to the standing timber stocks in response to different forms of forest investment highlight important differences between financial and biological change to timberland management. Results from the FASOM-GHG model indicate that changes to standing volume accumulation over the projection period are more sensitive to timber yield variation than changes in costs for forest establishment and timber management. When timber yields are increased by 15% (Scenario B1), the projected timber volume in 2100 is 14% higher than that for a 50% reduction in forest establishment and timber management costs (Scenario A1).
However, the difference in standing timber volume due to biological and financial changes does not arise until period 2040. Before then, the difference between amounts of standing timber stocks for the yield (Scenario Set B) and cost-related (Scenario Set A) scenarios is less than 1%. Larger differences arise after 2045, given the lag in effects when timber stands are regenerated and appreciable timber volumes accumulate for such stands. Because changing the timber growth rate in timberland stands or the costs to establish and manage new stands does not have a large impact in the first 40 yr, from a policy perspective, the timing of carbon storage is also important in addition to the level of storage. Neither increases in regenerated timber yield or financial incentive have an immediate impact on the amount of standing timber volumes.
These results point to the importance, in the long run, of improvements to timber yields, versus subsidies to timberland establishment and management costs, to store more forest carbon through increased amounts of standing timber stocks. Even if increasing amounts of standing timber volumes depressed stumpage prices, the increased levels of growth in regenerated stands would promote volume accumulation throughout the projection. The model with perfect foresight will increase harvests in advance of anticipated increases in investment and inventory levels, so as to maximize the discounted net value of timber harvests. This results in standing timber volume or inventory levels being the highest at the end of the projection for scenarios with timber yield increases. In contrast, there are scenarios that reduce harvest and boost inventory levels in the initial periods, such as decreased timber yield for regenerated stands and a restriction on forest investment that eliminates tree planting.
If timber inventory levels are to increase monotonically throughout the projection period (out to 2100), then increased forest investment is required to produce regenerated timber yields that are at least 35% larger than baseline levels. Technological improvements, such as improvement of genetic material, may play a role in any such yield boosts (e.g., Alig et al., 1999b), but also could affect land prices and lead to some conversion of forests to agricultural use.
At the other extreme, if no active investment in timber growing takes place (i.e., all natural regeneration representing reduced forest investment) (Scenario C2), then the timber inventory level by 2100 could be 17% lower than the base case. The aggregate inventory reduction would be particularly large in the South, which has a disproportionate amount of planted stands compared to other regions.
Although changing the timber yield levels has the greatest long-run impact to inventory levels, there is also a significant level of uncertainty. Little is currently known about the response on the stand level to global climate change (Burton et al., 1995), prompting sensitivity analyses of effects on timber yields (e.g., McCarl et al., 2000). Increasing the level of management, specifically on NIPF land, has the potential to increase levels of growth (Alig et al., 1999a). Intensification of forest management is sometimes viewed as the adoption of a complex regime of practices such as site preparation, planting, competition control, precommercial thinning, and so on. In practice, however, intensive management may involve nothing more than ensuring prompt and adequate regeneration after harvest or adjusting the form of partial removals to favor more rapid growth of residual trees. The effect of more intensive management, whatever its specific form, is to raise rates of forest growth and expand inventories on the available timberland base. Other ecosystem services that are related to the rate of growth and extent of inventory (e.g., CO2 uptake, certain types of wildlife habitat, or visual amenities) may be enhanced as well. There are also potential gains in forest growth from elevated levels of CO2 in the atmosphere. However, such estimates of increased level of growth from rising levels of CO2 are variable (Joyce and Nungesser, 2000). Additional aspects of global climate change make the potential for increased levels of stand growth uncertain. The lag effect between global climate change and biological response adds to this uncertainty (Alig, 2003). Also, the possibility of increasing temperature and decreasing precipitation is also a factor that could reduce forest growth projections.
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONHISTORICAL TRENDS IN FOREST...METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Our results point to the suite of biophysical–ecological, economic, and social factors that affect the amount and cost of carbon stored in forests. In addition to jointness in production for carbon and timber volumes, some factors interact, such as the ecological and economic factors that affect forest type transitions (e.g., Alig and Butler, 2004). Ecological successional trends can be altered by private timber harvest and regeneration that are driven by economic factors. Transitions among forest types could also be affected if owners recognize opportunity costs of storing carbon in forest ecosystems. Accounting for what happens across ownerships can be important, too, in that social differences in how forests are managed are reflected in the significantly lower timber harvest rates on federal timberlands. This may allow substantial buildups in standing timber volumes and carbon storage on such public timberlands (Alig et al., 2006; Smith and Heath, 2004), but also affect opportunity costs and carbon markets involving private forests.
One future research area pertains to simulation of carbon markets involving forests. This would include examining optimal mixtures of forest- and wood product–based carbon, both across time and space (e.g., regions). Although most attention in carbon storage analyses has been directed at afforestation and plantations, a broader policy viewpoint should include fate of carbon in harvested wood products and how to prolong lives of products in an efficient manner. The availability of many types of substitutable products and many sources of supply for any given forest product act to reduce the price impacts of supply shifts in forest products markets. Demand for timber products will also continue to grow. The United States has fairly stable per capita consumption of wood and paper products, at one of the highest levels in the world. Storage of carbon in wood and paper products is substantial, as in 1990 approximately 145 Tg of carbon, or 11% of the level of U.S. emissions, was harvested and removed from forests for products (Skog and Nicholson, 2000).
Given the joint production nature of forest ecosystems, carbon-related policies have the potential to usefully augment existing or future forest policies, and can have a positive effect on forest ecosystem stewardship. However, it is important to recognize the potential value of integrating carbon-related policies with others, such as enhancing biodiversity. Forests produce multiple goods and services, and climate change strategies can affect biodiversity and other environmental elements. For example, afforestation incentives could be targeted to jointly reduce atmospheric greenhouse gases, mitigate forest fragmentation (e.g., Alig et al., 2005), enhance biodiversity, and augment timber supplies, or some other combinations of those environmental attributes.
|
ACKNOWLEDGMENTS |
|---|
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONHISTORICAL TRENDS IN FOREST...METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Crop Science | |||
| Journal of Natural Resources and Life Sciences Education |
Vadose Zone Journal | ||||
| Soil Science Society of America Journal | Journal of Plant Registrations | The Plant Genome | |||
