Carbon Sequestration

Transcription

1 Carbon Sequestration 1. Summary and overview This chapter covers the opportunities to manage land and water systems to retain or enhance their value as carbon sinks. Some of the land use changes involved (i.e. afforestation) are defined under the Kyoto protocol as being eligible for credit against national GHG reduction targets; others are not yet eligible for consideration under Kyoto protocol, but may be substantive enough for consideration in state implementation plans. Many of the ecosystem-based carbon (C) sequestration opportunities are one-time, limited opportunities to rebuild C supplies in depleted ecosystems back toward a general equilibrium representing the capacity of the site under current soil, climate, vegetation, and management conditions. Once this level is achieved, further increases become increasingly unstable more difficult to achieve in some instances, or more difficult to maintain. Some opportunities, such as encouraging organic soil formation in wetlands, expanding the use of stable wood products, and utilizing biomass to replace fossil fuels as an energy source are more likely to be sustainable because they are less bound by ecosystem limits. Forest ecosystems that are currently overstocked with biomass are ecologically unstable, and may need active management to remove biomass and dispose of it in a GHG-friendly manner to avoid major wildfire emissions that can not only reduce current terrestrial C stocks, but degrade soils so that future sequestration rates are severely reduced. 2. Inventory of terrestrial sinks 1. Agriculture 1. cropland Most of the stable carbon in agricultural systems is held in the soil, since the majority of agricultural vegetation is short-lived and rapidly consumed or decomposed. Soil organic carbon is the food and energy source for soil biota, as well as the locus for much of the soil s stock of mineral nutrients. It is important in stabilizing soil structure, increasing water holding capacity, and buffering the soil s chemical reactions. Increasing soil organic carbon (SOC) content is, therefore, one way to improve soil quality and productivity. Improving agronomic productivity and reducing or mitigating emissions of greenhouse gas from agricultural soils occur simultaneously, so changing farm practices to improve cropland s capacity as a GHG sink is in the interest of farmers as well as air quality planners. 1 In dealing with soil sinks, whether on cropland or other agricultural systems, it is probably necessary to deal with periodic inventory data rather than the annual activity data that is available in other sectors. There is very little data on annual activity levels that would support any other estimate. Monitoring soil activity through such measures as CO 2 respiration are feasible at the research level, but not at the larger scales. The Natural Resources Conservation Service conducts its Natural Resource Inventories on a 5-year cycle, which provides a periodic, comparable inventory from which estimates of land use change on the Nation s non-federal lands can be developed. 2 Estimates of annual tillage practices on cropland are available from the Conservation Tillage Information Center. 3 The conversion of native forest and grassland ecosystems to cultivated agriculture causes a loss of SOC that is well documented. The losses are highest in the first few years of STAPPA Carbon Sequestration Draft 1 July 20,

2 cultivation, then tend to level off. The degree to which SOC has been depleted from its historic range tends to establish its capacity as a future sink, since it is generally agreed that, upon improvements in the management system that raise crop yields, return higher levels of crop residue to the soil, retard SOC decomposition processes, or reduce the disturbance and aeration associated with cultivation, SOC levels will return to levels at or near their native condition. 4 An exception to this is in the case of irrigated desert soils, whose very low native SOC stocks have been raised by the additional plant material incorporated by cultivation and maintained by higher moisture and fertility levels. The total SOC stock in U.S. croplands is estimated at 17 billion tons, or about 51 tons per acre. 5 This would mean, for the average upland soil, an organic carbon content of around 2 to 4 percent. It is estimated that these soils have lost through cultivation, and therefore could regain through improved management, an additional one percent SOC, or about 15 tons of C per acre. This will vary considerably, of course, due to different soil characteristics, agricultural systems, and the current condition of the soil. Localized estimates of cropland SOC conditions, and potentials, can be obtained through the local offices of the Natural Resources Conservation Service. 6 SOC levels, and therefore any additional CO 2 sinks created by improved cropland management, are subject to loss if the management reverts to prior practices. Programs that seek to utilize cropland soils as a means of reducing atmospheric greenhouse gases must, therefore: Recognize that this is a one-time sequestration opportunity, designed to build SOC levels from a current level to a higher, but ultimately limited, level; and, Include a plan for maintenance of the new, higher SOC levels once they are achieved. In addition to the opportunities associated with improved management of the soils that remain in cropland use, there are major opportunities to rebuild SOC levels by converting marginal cropland back to permanent grass, trees, or wetland. Those land uses, and their CO 2 sink potential, are discussed below. 2. pasture and range There were an estimated 126 million acres of pastureland and 399 million acres of rangeland in the United States in 1992, according to the 1992 National Resource Inventory. In addition, there were 34 million acres which had been converted to grass from marginal crop and pasture since 1982 under the Conservation Reserve Program. All together, these grassland systems constitute almost 38 percent of the Nation s non-federal lands in the conterminous 48 states. 7 The land use is fairly stable for rangeland, but 21 million acres had been added to pasture between 1982 and 1992, while 27 million acres had been converted, mainly to cropland or forest. Estimating the carbon dynamics on these land use changes in any accurate way is not possible without knowing the soil types, conditions, and management practices involved, but it is safe to say that, on the 12 million acres converted from pasture to cropland in that decade, SOC levels dropped fairly rapidly for the first few years of cultivation. Tree planting on 8 million acres may have added some SOC in addition to the tree biomass, but how much is unclear. There is some evidence that, in converting from grassland to forest, the SOC levels rise rapidly in the organic layer that constitutes forest duff, but may decline in the deeper mineral soil layers as the old grass roots rot away and tree roots do not provide replacement SOC. STAPPA Carbon Sequestration Draft 1 July 20,

3 For the land that remains in pasture and range, the principal use is for grazing, and the SOC balance is affected by whether the grazing management is causing the vegetation to increase or decline. In all likelihood, the net change is probably negligible, since for most of these lands, the management has remained reasonably stable for years, and the SOC levels have adjusted to the physical and management regime. A. Forests 3. Carbon dynamics in America s forests The woody materials in forests are about half carbon on a dry weight basis. 8 In total the organic carbon stored in the vegetation; litter, humus, and woody debris; and soils of U.S. forests amounts to 60 billion tons. 9 This stored carbon amounts to about 40 times the Nation's annual carbon emissions of around 1.5 billion tons. 10 The largest part of the stored carbon, some 61 percent, is found in the forest soils. About 29 percent of the stored carbon is in the trees, and the remaining 10 percent is in the woody litter, debris, and humus on the forest floor as well as the understory vegetation. There are major differences in the amount of carbon stored in the forested regions of the country. Some 25 billion tons, 41 percent of the total, is stored in the forest ecosystems of the Pacific Coast, mostly in Alaska. About 25 percent is stored in the forests in the North, 14 percent in the Rocky Mountains, and 21 percent in the South. 11 These regional differences reflect differences in climate and in the age and density of the forests. The cool climates of the Pacific Coast and North slow the oxidation of carbon in the soils, in dead trees, and in the woody materials on the forest floor. The Pacific Coast region has big areas of old, undisturbed forests that contain large volumes of carbon. Carbon storage in forests is constantly changing in response to land clearing; tree planting on lands that have been used for crops and pastures; timber harvesting; and the natural regeneration, growth, and death of vegetation. In recent decades, carbon storage has been rising because timber growth has been higher than the total of harvest removals and mortality, with a consequent increase in timber inventories. Between 1952 and 1992, for example, carbon storage on forest lands in the conterminous United States increased by 12.4 billion tons about 25 percent. 12 Timber growth is substantially above removals in the hardwood forests, and carbon is accumulating in the major hardwood regions. The largest increase is in the Northeast, but there are also big increases in storage in the Southeast and on the Pacific Coast. In some areas in the South Central region, removals are above or close to growth, and the carbon accumulation is quite small. Mortality increased by 24% between 1986 and 1991 in all regions, on all ownerships, for both hardwoods and softwoods. 13 Obviously, the continued increase of carbon storage in U.S. forests is not assured if increasing mortality rates are experienced in the future. 4. Managing Carbon Balances in Forests STAPPA Carbon Sequestration Draft 1 July 20,

4 Carbon accumulates within a forest over time, as the forest changes due to tree growth and ecological succession. Over many years, the Forest Service has measured the growth of different tree species and forest types on different soil types. These growth and yield models have now been converted to carbon accumulation models. 14 Two examples illustrate the use of these tables. In loblolly pine plantations of the South, there are two significantly different growth yield models that can be used. One is the estimate of managed yields the yields that good managers consistently achieve. The second is the inventory yield the yield that is realized over the average of all ownerships and managers. Figure 1 shows the difference, which can be as much as 60% over an 80-year rotation. For individual projects on good sites, where management is assured, the high estimate of carbon sequestration is reasonable. For state or national policy, where general response is sought, the lower estimate is most reasonable. Another example might be the old growth Douglas-fir stands of the Pacific Northwest. These forests have enormous stores of carbon on site, and while the accumulation is slow because of the maturity of the trees, it continues to occur. If our goal is to retain stored carbon for the next few decades, we protect these forests. Harvesting them, and removing all the dead wood from the site without using it to offset fossil carbon, would result in a net loss of carbon that would take decades to recover. If our object is to increase carbon storage over time, however, then harvest and replanting becomes the best option. 15 The reason for this somewhat counter-intuitive conclusion is found in the research that has tracked the fate of forest carbon following harvest. This has demonstrated that a significant amount of the carbon remains in terrestrial storage, often as products in use or in material that is retained in landfills or dumps. 16 Another significant percentage is utilized to replace fossil fuels as an energy sources. As long as this comes from forests that are managed sustainably, it represents a short-term recycling of carbon in and out of the atmosphere, replacing an emission from the stored fossil sources, so it is a net replacement in terms of carbon emissions. The effect is that, if we study the effect of long-term forest management schemes on carbon balances, the managed forest, with products utilized for long-term storage, continues to build terrestrial carbon storage rotation after rotation, as the amount of products continue to reside for significant periods of time in storage. This can be illustrated by looking at the probable effects of different management schemes on several different forest types. 17 Evaluating the carbon storage and accumulation in U.S. forest ecosystems has been done by comparing forest inventories over time. These inventories, which have been carried out for STAPPA Carbon Sequestration Draft 1 July 20,

5 decades, published data in terms of tree species, size classes, and merchantable volume. As a result, they have focused largely on the lands that were available for timber production (timberlands defined as lands capable of producing 20 ft 3 or more of merchantable wood per year, and available for timber management). Other forest lands, such as parks and wilderness areas, or large remote regions such as interior Alaska, have received far less inventory attention, and therefore the estimates of their carbon dynamics are less reliable. In the first comprehensive effort to establish the carbon dynamics of U.S. forests, Richard Birdsey of the Forest Service estimated carbon storage for 4 separate components (trees, soil, forest floor, and understory vegetation) for each of the forest types identified in the 1987 forest inventory data base. 18 The annual growth of forests results in an accumulation of around 508 million tons of carbon, while the total removal resulting from timber harvest, land clearing, and fuel wood use amounts to 391 million tons of carbon. The difference suggested that U.S. forests are sequestering additional carbon at the rate of around 117 million tons per year. 19 In addition, trees dying in the forest due to a variety of causes represent around 83 million tons of C per year, but much of that remains in the forest for some time as snags or down woody debris. Another way of estimating the annual sink of U.S. forests is to compare the inventories over time. As Figure 2 illustrates, U.S. forests have been steadily gaining in stored carbon since In this calculation, it was estimated that carbon stored on the forest land in the conterminous United States had increased by 11.3 billion metric tons in the 40 years, for an average of 281 million metric tons per year. 20 These estimates ( ) probably bracket the baseline for forest ecosystem carbon sinks in the U.S. 5. Ownership and use characteristics In developing the basic stock estimates for establishing baseline forest carbon levels and trends, little distinction is made between forests on the basis of ownership or use. Those factors will, however, play heavily into the kinds of changes that can be proposed in the name of air pollution reduction. They also play very heavily into strategic planning at the state and local level, because the ratio of public to private forests is very different from place to place, as shown in Tables A-1 and A-2. The distinction between forests and timberland is of little importance in considering the existing forest as a naturallychanging stock of carbon, but it is very important in addressing potential changes through management. Virtually all of the management opportunity lies on the timberland, primarily because that is the land that is productive enough to attract investment, or that is legally available for management activity. B. Wetlands/peat bogs The cultivation of wetlands, peat bogs, or other highly organic soils leads to a continuous decline in SOC, since additional organic material is opened up to aerobic STAPPA Carbon Sequestration Draft 1 July 20,

6 decomposition with continued cultivation. Restoring these soils to a wetland condition and maintaining them as wetlands converts them into a carbon sink that is, so long as the wetland condition holds, sustainable. C. Deserts Deserts are generally very small contributors to either sinks or stocks of terrestrial carbon, since SOC levels are generally very low, as are standing vegetation stocks. With the addition of irrigation water, desert soils can become very productive and, in the process, SOC levels can rise, providing a short-term sequestration opportunity. In their native state, however, deserts are unlikely to provide any significant opportunity to address climate issues. Under climate change conditions that alter temperature or moisture, deserts could become a modest sink or source, depending on the effect of the change on net primary productivity of the ecosystem. 2. Sequestration levels 1. Current 1. baseline estimates for change in stock calculations Historical and baseline estimates for agricultural soils can be obtained from soil survey data published by the Natural Resources Conservation Service. In general, for soils under rainfed agriculture, the estimated pre-cultivation organic matter levels can be obtained from soil survey data, and probably represent the highest level that is feasibly obtainable on the soil through improved management or conversion back to original vegetative cover. For irrigated soils, particularly those of desert origin, it is possible to achieve elevated levels through incorporation of additional plant material in agricultural operations. If irrigation were to cease, however, these soils would rapidly lose that additional carbon and return to levels consistent with the vegetative growth possible under non-irrigated conditions. Historical and baseline estimates for SOC levels on grassland soils can also be obtained through the NRCS soil survey data base. Baseline estimates on existing forests need to be measured by standard forest mensuration techniques. Since most of those methods historically were developed to estimate the amount of merchantable timber, by size class, in a forest stand, the results may need to be adjusted to reflect the total carbon content of the forest. That has been done by forest component (trees, soil, forest floor litter and debris, and understory vegetation) and age of forest stands for most of the common forest types in the United States Projected 1. business as usual (base case) Under a continuation of cropland management techniques similar to those of the past, most soils that have been in cultivation for more than years will probably remain at roughly their current SOC levels, assuming that soil erosion levels are being controlled. If soil erosion is occurring, the SOC levels may continue to gradually decline, as soil productivity is diminished. Under rangeland management that maintains existing vegetation, SOC levels will probably remain roughly the same, as well. Erosion is not a problem on well-managed rangeland. If soils are being eroded, however, SOC levels may decline as productivity is affected. Forest growth and biomass accumulation will continue to increase over time on most forest situations. The growth and yield curves developed by Birdsey can be used to gain rough estimates of the growth into the future. Business as usual management may include STAPPA Carbon Sequestration Draft 1 July 20,

7 many options, from hands off preservation to intensive silvicultural efforts to improve growth, and these may affect both carbon sequestration or, on the other hand, increase the risk of significant carbon release through wildfire. As a result, baseline estimates for individual forest situations should be based on a realistic appraisal of what the current owner or manager is planning to do. b. possible confounding factors (1) CO 2 /temperature/moisture/nutrient-enhanced growth Elevated CO 2 levels, increased temperature, and altered moisture or nutrient conditions can affect ecosystems in ways that are difficult to assess. It has been predicted that elevated CO 2 levels will enhance growth more in some species than in others, but this has not been confirmed in ecosystem studies. 22 Altered temperature and moisture conditions will affect forest growth, but until predictive models are more reliable in terms of local or regional impacts, any predictions in the effect on future forest growth rates seem speculative at this time. The same can be said for nutrient changes, although more is known about the degree to which airborne deposition of chemical nutrients is currently taking place. Data and maps on nutrient deposition can be downloaded for use in state planning. 23 However, reliable data on the impact these deposits currently have on forest growth rates or are likely to have on future growth rates are lacking. (2) Temperature enhanced respiration/pest problems Some researchers postulate that, although changes in environmental conditions may enhance growth, a rise in temperature may also have the effect of decreasing net forest growth, and therefore reduce forest sequestration rates. These effects could happen in two ways: (a) by enhancing respiration and decomposition rates faster than growth rates are increased, thereby reducing net primary productivity; or (b) by favoring insect and disease vectors that would become more effective in attacking forest plants, thus weakening and killing them more effectively. In an example of the latter effect, Alaskan researchers have noted that recent years, with milder winter weather, result in early emergence of the Spruce bark beetle, thus enabling the insect to complete its life cycle in one year rather than two. There is concern that such a trend could tip the balance in favor of the beetle, leading to wider epidemics. 24 The major risk to natural ecosystems may be that changing environmental conditions may alter species adaptation, causing some species to lose footholds faster than they can gain new ones through migration. Some ecologists have predicted that, as a result of climate change, the terrestrial biosphere will probably become a source rather than a sink for carbon over the next century Options for Increasing Sequestration 1. Agriculture 1. Soils 1. Cropland (1) Conservation tillage this practice, which replaces cultivation as the primary means of seedbed preparation and weed control with a variety of approaches that retain crop residues on or near the surface of the soil, is designed primarily as a means of controlling soil erosion from wind and water. Its effects, however, can include a STAPPA Carbon Sequestration Draft 1 July 20,

8 buildup of SOC on most soils, due to the increased residue input and reduced decomposition due to less aeration and disturbance of the upper soil layers. Nationally, it is estimated that almost half (49%) of the total potential for improving CO 2 sequestration on croplands could be achieved by the widespread adoption of conservation tillage and improved crop residue management. 26 (2) Improved cropping systems These are practices such as better soil fertility management, improved crop rotations, and winter cover crops. Nationally, they are estimated to be able to provide around 25% of the total cropland CO 2 sink potential. 27 One example of such a practice is greater use of perennial forage crops in the rotation, which adds root mass and additional SOC to the soil, reduces cultivation, and provides protection from soil erosion. 28 (3) Intensification of prime farmland management Meeting the world s need for food and fiber, while protecting environmental values, provides an incentive for intensifying the use of the very best land for agricultural production. While the CO 2 sequestration on the prime land itself may be modest (except, perhaps, in the case of irrigated desert and dryland soils, where enhanced productivity is related to increased SOC levels in many situations), a major benefit lies in the opportunity to convert marginal croplands, organic soils, or wetlands back to native condition or biofuel production where they are no longer needed to grow food. (4) Reduced soil erosion Reducing soil erosion from wind and water is a primary goal of the soil and water conservation program that can have an effect on both air resources and GHG balances in addition to its values for protecting water quality and farm productivity. Erosion that moves soil from one place to another (including the SOC attached to the soil particles) is usually not counted in C inventories because it does not represent a loss of C, just a movement on the landscape. What it represents, however, is a productivity loss in the eroded soil that is often not replaced by increased productivity in the sedimentation area. When that occurs, the annual C uptake of the degraded site is lessened, which results in lower production of biomass, which in turn results in less biomass returned to the soil and lower SOC levels. On forested sites, it can mean lower biomass production for many years, if not decades. Thus, programs that prevent soil erosion have positive impacts on GHG balances. The other positive impact lies in lowered PM levels from blowing dust, which can be a serious air pollutant during certain times of the year when crop coverage on the land is limited and high wind speeds are common. Practices such as conservation tillage that leave a protective layer of crop residue or mulch on the soil surface during these periods can reduce dust blowing significantly. At the national level, it is estimated that wind erosion on cultivated cropland was cut almost by half between 1982 and 1992, largely through the widespread adoption of conservation tillage and improved crop residue management practices Pasture and range (1) Improved grazing practices Managing grazing to maintain healthy, productive forage stands can maintain SOC levels at or near native conditions on many soils. Where SOC levels have been depleted by overgrazing, improving grazing practices may provide a significant sink opportunity for the restoration of the depleted SOC. STAPPA Carbon Sequestration Draft 1 July 20,

9 Localized soil and range condition surveys are needed to develop quantitative estimates of this potential. (2) Wildlife habitat restoration In some programs such as the Conservation Reserve Program (CRP), permanent grass cover is restored and then left unharvested and ungrazed as a means of protecting against soil erosion and improving wildlife habitat. In addition to its recognized wildlife benefits (some upland bird species such as lark buntings were estimated to increase 10-fold in population density in CRP versus associated croplands. 30 ), the estimated rates of SOC accumulation on CRP land were 220 to 1,200 pounds per acre per year in a 16-state study encompassing the Pacific Northwest, Great Plains, and western Corn Belt. The highest rates were found in the western Corn Belt Biomass energy production 1. Dedicated energy crops This approach can include grasses such as switchgrass or woody species such as hybrid poplar which are grown specifically for conversion to energy either through direct combustion to produce electricity or chemical conversion to liquid fuels. Because of the need for intensive management, mechanization, and high yields, these crops normally compete for cropland rather than being suited to existing forest or rangelands. The greatest C sequestration benefit is the substitution or offset effect gained by leaving fossil fuels in the ground. There are, however, also significant SOC and standing biomass increases on these lands compared to the cropland they replace. 32 Delivered net energy crop yields from good cropland in the U.S. are in the range of 2 tons of Carbon per acre, and yields in the 4 tc/ac/yr range are believed to be possible if production expanded and technology continues to progress. 33 Where these biomass fuels are used in co-firing with coal, the benefits include reduced SOx and NOx emissions, as well as reduced net CO 2 emissions. 2. Sugar, starch, or oilseed crops These include annual or perennial crops in which only a portion of the crop is used for energy, usually for liquid fuel production. Examples include sugarcane and corn, which can be converted to alcohol or ethanol fuels, or oilseed crops such as rapeseed that can be processed into biodiesel that burns in modified diesel engines. Ethanol produced from corn is the most widespread use of the technology in the U.S. today, with about 1.7 billion gallons of ethanol production capacity in sold operation. 34 Two processes (dry milling and wet milling) are used. Each produces about gallons of ethanol per bushel of corn, along with animal feed byproducts that contain 21 to 60% protein. The limit to the value of these crops as CO 2 sequestration strategies is due to low net energy efficiencies and fossil fuel inputs required in their production. Producing one energy unit of rapeseed biodiesel requires about units of fossil energy, and net efficiencies in the range of 13-20% are reported for other grain and root crops. 35 Sugarcane, which provides much of its own processing heat through burning of the bagasse, and palm oil, which has shown considerable promise elsewhere, are not available as options in much of the U.S. These efficiencies are, however, being improved and costs are coming down, due to continued research and development. The STAPPA Carbon Sequestration Draft 1 July 20,

10 projected cost of biomass ethanol has come from around $4.63 per gallon in 1980 to about $1.22 per gallon in a modern plant, largely due to the introduction of superior enzymes and process designs. 36 Further technological developments promise to lower costs to less than $1 per gallon, and those lower costs represent comparable improvements in energy efficiency and CO 2 mitigation value. 3. Crop residues and byproducts There are opportunities to utilize crop residues for energy production, either in direct combustion or chemical process, but they are highly variable from crop to crop and place to place. There are limits imposed by the feasibility of collecting and transporting wastes, as well as to the extent to which crop residues can be removed from the land without adversely affecting SOC levels. In general, it is estimated that only 50% of the residues can be removed without adversely affecting SOC, and only about 25% should be considered recoverable for energy purposes Forests 1. Extensively managed In the following discussion, extensively managed forests are defined as those which are managed across large landscapes for a variety of purposes which may, but often does not, include timber production. Extensively managed forests are generally wild ecosystems, depending on natural regeneration for forest recovery following a disturbance such as windstorm, wildfire, or timber harvest. Many of them are public forests, and some are in parks, wilderness areas, or other protected areas that preclude timber production. Where timber harvests are allowed and conducted, they are normally some type of partial cut rather than clearcut, to allow the remaining stand to re-seed and regenerate the forest. (Forests where practices such as thinning, pruning, fertilization, or replanting are done are considered to be intensively managed.) Forests often hold enormous stores of carbon (up to 100 tons per acre or more in the old growth Douglas-fir forests of the Pacific Northwest). These standing stocks, while they seem stable to the eye, and often remain intact across several human generations, are subject to rapid change, either through natural disturbances such as windstorms or fire, or through human impacts such as timber harvest or land clearing. These events can quickly turn a forest from a carbon sink into a significant carbon source, so management goals in relation to climate change may involve either (or both) enhancement of existing sinks and prevention of unwanted sources. The carbon impact of different disturbances may depend primarily on how the wood is utilized following the disturbance. A windstorm may, for example, blow down a fairly large patch of old growth forest along the Pacific coast, repeating a disturbance process that has been historically common. If the trees are left on the ground, they will gradually rot, with the carbon recycled to the atmosphere. If the stand was made up of large, mature trees, the pile of decomposing wood may be several feet deep and cover the ground almost entirely. New trees may eventually poke up through it, but a fully regenerated stand will be decades, if not centuries, in emerging in some places. The area will remain a carbon source for many years, in all likelihood. If the downed trees catch fire, which is highly likely due to the flammability of the dead branches and foliage, most of the small fuels will burn, but often the big logs will just char. Where large wood, close to the soil surface, burns or smolders for days, high temperatures STAPPA Carbon Sequestration Draft 1 July 20,

11 may destroy soil carbon and, if extreme enough, cause permanent soil damage to the area affected. An immediate carbon emission will result from the burning of the vegetation and the soil organic matter, followed by subsequent emissions as the remaining organic material decomposes. This may be somewhat accelerated by the increased heat caused by black surfaces and the increased moisture due to the lack of big trees to take up soil water. Charcoal formation during the fire will lock some carbon up in a stable form, thus providing a small permanent sink. Forest regeneration may be more rapid due to the exposure of more mineral soil due to the burning of the forest floor material and the mineralization of nutrients from the burned foliage. If the downed trees are salvaged and converted to lumber and paper use, much of the carbon will either be stored in long-term products or burned to produce energy, offsetting the need for fossil fuels. In general, the larger the trees, the more likely that the wood will go into large beams, construction materials, or other products with a longer life span in use. If the salvage is done with care, protecting soils from damage and leaving ample dead wood on the site to provide a carbon legacy for the regenerating forest, the new forest may regenerate much more rapidly than in either of the former two cases, and the carbon impact of the event will be minimized, both by the wood usage and the more rapid recovery. If, however, the salvage is done with destructive methods that remove all woody debris, disturb soils, and otherwise maximize carbon losses on the site, the net carbon impact will be far more damaging. How the land is treated becomes a primary consideration in assessing the carbon impact. A similar analysis can be made in the event of a wildfire that kills the large trees, but the process is reversed. The standing dead trees will eventually fall. The area may regenerate, reburn, or remain unforested for some time. Salvage of the dead trees may or may not be a wise move in terms of forest regeneration or reducing carbon emissions. The real effect can only be assessed when an actual situation can be evaluated and management options compared. In general (contrary to popular myth), few forest management options in such a situation can be generalized to be good or bad. It depends on the situation, and how the management activity is carried out. 1. management Extensive forest management focuses on maintaining the integrity and productivity of intact forest ecosystems. Practices may include the regulation of large ungulate (deer, elk, etc.) populations or domestic grazers (cattle, sheep, goats) to maintain vegetative diversity, protection of soils and streams from erosion and sediment damage through effective road placement and management or riparian area protection, mimicking of natural disturbance regimes through prescribed fire, or designing timber harvests to mimic natural wind or fire disturbance patterns. Much of this management will protect the integrity of the ecosystem, and therefore prevent major emissions, but the effect on sequestration rates is likely to be minor. Projects that claim to improve carbon balances on existing, extensively managed forests are often based on the claim that, without such management, the forest will be destroyed. In areas where forest clearing for other uses such as agriculture, pasture, or urban use is common, that may be the case. Such areas are rare in the U.S., however, particularly in the areas where extensively-managed forests are found. Claims for major carbon benefits from STAPPA Carbon Sequestration Draft 1 July 20,

12 changed management should be examined closely to assure that the base case (the withoutproject simulation) is realistic. 2. protection Protecting extensively-managed forests from destruction and major carbon emissions is largely a matter of protecting them from wildfire and/or land clearing. As noted earlier, land clearing is more of a problem in the developing world than in the U.S., but there are instances where it may be a possibility. In general, however, there will be little gained from attempts to address this issue through air quality programs. Most land clearing is associated with urban growth areas, so working through local land use planning and controls is the most logical approach to addressing the issue. Wildfire is a definite risk in extensively-managed forests, particularly in the forest types where fire return intervals have historically been fairly short. 38 A Century of increasinglyeffective fire suppression has left many areas so loaded with flammable fuels that a severe wildfire is virtually assured unless major efforts are made to reduce fuels and restore firetolerant conditions. It has been estimated that the current decade ( ) could see between 15 and 30 million acres of wildfire in the 11 Western States, and that most of the larger events will be well beyond the current capacity of fire management agencies to control or suppress. 39 To the extent that Western wildfires continue to be characterized by large, intense events that kill a high proportion of the older trees within the fire perimeter, they will set ecosystems back several hundred years, particularly in the ponderosa pine forests that are so extensive throughout the region. To the extent that they contain significant areas of highseverity soil impact, they will affect watersheds for decades, if not longer, and in the most severely damaged areas, affect ecosystem recovery and successional pathways. Thus, in addition to imposing enormous economic costs due to suppression activities, property destruction, and economic resources lost, there will be significant environmental damage as a result. The situation in the Western states suggests that forest protection efforts in many areas, well-meaning though they might be, will be of little avail, given the current condition of the ecosystems involved. 40 Forests may need to be intentionally altered, in terms of the vegetative structures, fuel amounts and arrangements, and canopy density before they will be in condition to withstand the periodic fires that tend to occur in the region. Where forest protection disallows this intentional vegetative manipulation, the protection effort is, in all likelihood, doomed to fail. The main question is not whether such forests burn, but when. One of the opportunities for increasing carbon sequestration on extensively-managed forests that is tightly linked to the control of other criteria pollutants is prescribed fire. The appropriate use of fire may not only reduce emissions through the conversion of large, stand-replacing wildfires into less intense, more natural wildfires, but it may also protect large trees from lethal damage, thus keeping the forest healthy, growing, and sequestering carbon. This situation creates a dilemma for air quality managers, because the Clean Air Act explicitly requires regulations that protect human health and visibility from damage due to impairment from man-made pollution. 41 The dilemma in many Western states is that, if prescribed fire and its effects are limited too tightly by the regulations, the untreated forests may be far more susceptible to STAPPA Carbon Sequestration Draft 1 July 20,

13 uncontrollable wildfires which release many times more pollution, and do so in fairly short time periods, leading to high, and sometimes locally hazardous, concentrations Intensively managed 1. afforestation An estimated 116 million acres of land that was biologically suited to growing trees was being used as marginal crop and pasture land in About half was in cropland and half in pasture at the time, and it was equally nearly divided in terms of its suitability for softwood and hardwood forests. The total opportunity it offered was between 1.5 and 5.2 billion cubic feet of wood a year, which would have been somewhere in the range of 36 and 131 million tons of carbon added to the forest inventory. Some of that opportunity 4 to 5 million acres has been captured by tree planting under the Conservation Reserve Program since 1985, but there are over 100 million acres still available for trees if the appropriate incentive to landowners can be created. Afforestation projects are reasonably simple to evaluate, in terms of the potential increase in the carbon sink. Growth models exist for most soil and forest combinations, and a plan can be developed to achieve a high probability of success in reaching the planned growth rates. For many states, tree planting projects that enlarge the forest base and create new, rapidly-growing forests are a prime opportunity to enhance forest sinks. 44 Average annual sequestration rates in the range of 1 to 3 tons of carbon per acre are commonly achieved. 2. new varieties Industrial forest companies work to achieve faster tree growth and higher-quality timber through tree selection programs that test and select the most desirable individuals from a highly diverse genetic population. Tree selection takes many years, because most trees do not reach sexual maturity quickly, but the programs have been in effect for years in many places, and improved strains are being planted in most commercial forest operations. While there have been objections to the use of genetically-improved stock on the basis of simplifying the gene pool, forest geneticists argue that what has changed are the dominant characteristics, not the range of the gene pool itself. Those criticisms are certain to be heard, however, as genetic engineering replaces selection as the featured means of developing improved varieties. Where individual trees utilize sunlight, water and nutrients more effectively, or resist insects and diseases better, their additional growth rates translate directly into enhanced carbon sequestration. If they produce a higher-quality wood product, a higher proportion of the harvested wood is likely to end up in long-lived products such as building materials or furniture, so that has a positive sequestration effect, as well. Programs to encourage the use of better-adapted, more productive trees in intensively-managed forests should produce positive results for state climate change plans, while doing little or nothing to adversely affect criteria pollutant emissions. 3. longer rotations Encouraging longer rotations between harvest cycles can result in both a higher average annual level of carbon storage on the forest site, and the production of higher-quality wood STAPPA Carbon Sequestration Draft 1 July 20,

14 products as the result of larger logs. For many commercial forests, the main incentive is financial, so any programs that produce improved net revenues through higher prices for better material, tax incentives, or other financial instruments will encourage the use of longer forest rotations. 4. improved harvest techniques A related opportunity exists through changing timber harvest methods. Timber harvest is, except for intense wildfire, the most disruptive event in the forest life cycle. Attention to the effects of forest harvest methods on carbon sinks will lead to methods that: * Leave enough canopy cover to shade the soil and keep soil temperatures reduced; * Leave foliage and small branches on-site to minimize nutrient export; * Burn slash carefully, and leave adequate snags and large woody debris as a carbon legacy for the ecosystem; and, * Minimize soil disturbance and movement, through mechanical activities or erosion, to prevent export of soil carbon or accelerated organic decomposition due to aeration. 45 The practice of clearcut harvesting attracted negative public reaction to its appearance and effect on the forest, and foresters failed to convince the public that it is a necessary and useful practice. In 1992, the Forest Service declared a new policy to minimize the use of clearcutting as a harvest method wherever other methods are available. The Sustainable Forestry Initiative encourages industrial foresters to voluntarily limit the size of clear-cut (some states also have enacted size limits). Reports by participating members of the American Forest and Paper Association indicate that the average size of industry clear-cut was 57 acres in 1997, down from 66 acres in This should be a positive change in terms of carbon sinks and the effects of forest harvest upon them. Particularly in its most extreme forms, where the slash, stumps, and debris were piled and burned, the volatilization of carbon, both in the debris and the soil, was maximized. Although little evidence of site deterioration has been found, it seems inconceivable that interrupting the normal cycles in such an aggressive fashion would go without impact. 5. more efficient utilization Waste from forest harvests, whether in the woods or in the manufacturing process, represents carbon that is lost back to the atmosphere, either through decomposition or burning. Reducing waste losses in manufacturing has been minimized in recent years by air and water pollution controls, so that today most manufacturing waste is immediately recycled or burned for energy production within the facility. Waste in the timber harvesting process comes from broken or damaged pieces, improper cutting, or damage to standing timber in the felling and skidding processes. Most of that can be avoided by properly trained and equipped workers and, since the economic incentives favor the minimization of waste in most cases, this can be avoided. Where professional help has been retained to design and oversee a timber harvest project, or where the loggers are trained and given incentives to reduce waste, wood utilization rates are about as high as can reasonably be expected. Exceptions are most likely to occur on small private holdings that do not utilize professional assistance, or on public lands where low-bid contracting provides incentives for hasty work and wasteful practices. STAPPA Carbon Sequestration Draft 1 July 20,

15 6. increased use of wood in place of more energy-intensive substitutes In the main market for wood products building materials the competition comes largely from the steel and masonry industries. The steel industry has developed framing materials that compete well in price and performance for use in homes and other building applications, and that out-compete wood when timber prices rise. Its claim to being a green product lies in its high degree of recycling. Concrete and brick make much of their local abundance in many areas, and long life in use. Wood counters with its claim of renewability. The question of total environmental effect is a complex one, and several parameters need to be considered. One of the measures relevant to the climate policy debate is total energy expended in the life cycle of the product. This estimates the relative amount of energy involved in extracting the basic material, processing or manufacturing the product, fabricating the building, occupying it, and disposing or recycling the material at the end of its useful life. On this measure, wood competes well. An interior wall constructed with steel studs is 3 times more energy intensive than its wood counterpart, meaning that the CO 2 emissions are also 3 times as great. 47 If the analysis is extended to an exterior, load-bearing wall, the wood advantage increases to something on a 1:4 energy and CO 2 ratio with steel, even where 50% recycled steel is assumed, because of the thicker steel needed for structural strength. On another environmental parameter water consumption steel assembly requires some 25 times more water than its wood counterpart. This increases the polluting effluents associated with industrial water use, so if either water shortages or pollution control costs are a locally-important environmental issue, this is a factor to consider. While the relative environmental advantages of wood over steel seem significant, the total annual climate impacts are modest by comparison with many of the other forestry-related opportunities to affect CO 2 emissions. The life-cycle model results reported by Meil indicate that, for an interior wall, wood construction results in about 0.35 tons of CO 2 emissions per 1,000 ft 2 of wall while steel results in about 1.07 tons. Comparable estimates for exterior walls are 0.44 tons CO 2 per 1,000 ft 2 for wood and 1.76 tons for steel. In 1995, U.S. housing starts were around 972,000, with the average house utilizing around 4,260 board feet of framing lumber to construct an average of around 1,600 ft 2 of interior walls and 2,170 ft 2 of exterior walls. 48 These estimates can be used to test the potential CO 2 effect of the steel industry s goal of achieving 25% of the U.S. market for framing materials in housing construction. Table 1 indicates the impact of options for using wood and steel. The difference between all-wood and all-steel about 1 million tons C per year in terms of CO 2 emissions is only a partial measure of the climate impact of the two competitors, because it does not account for the wood wall s value in storing C for many years, which would increase the wood s advantage. Table 1. Estimated emissions from alternative building materials used to frame new residential construction in the U.S., based on 1995 construction estimates. Framing Option CO 2 Emissions C Emissions STAPPA Carbon Sequestration Draft 1 July 20,