produce more CH, per unit of feed consumed. Confined feeding operations utilizing balanced rations that properly manage digestion of high-energy feeds also can reduce direct emissions, but can increase indirect emissions from feed production and transportation. CH, produced in animal waste disposal systems can provide an on-farm energy supply, and the CH, utilized in this manner is not emitted to the atmosphere. Overall, potential global reduction of CH, emissions amounts to about 35% (15-56%) of emissions from agriculture.

Nitrogen is an essential plant nutrient; however, it is also a component of some of the most mobile compounds in the soil-plantatmosphere system. Since nitrogen is the major component of mineral fertilizer, there is mounting concern over the extent to which high-input agriculture loads nitrogen compounds into the environment. Nitrogen budgeting, or an input/output balance approach, provides a basis for policies to improve nitrogen management in farming and livestock systems, and for mitigating its environmental impact. Management systems can decrease the amount of nitrogen lost to the environment through gaseous losses of ammonia or N,O, or through leaching of nitrate into the subsoil. In some cases, improved efficiency is achieved by using less fertilizer, in other cases, it can be achieved by increasing yields at the same nitrogen levels.

The primary sources of NO from agriculture are mineral fertilizers, legume cropping, and animal waste. These losses often are accelerated by poor soil physical conditions. Some N2O also is emitted from biomass burning. Improvements in farm technology, such as use of controlled-release fertilizers, nitrification inhibitors, the timing of nitrogen application and water management should lead to improvements in nitrogen use efficiency and further limit N2O formation. The underlying concept in reducing NO emissions is that if fertilizer nitrogen (including manure nitrogen) is better used by the crop, less NO will be produced and less nitrogen will leak from the system. By better matching nitrogen supply to crop demand and more closely integrating animal waste and crop residue management

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7.1 Introduction

Forests constitute both a sink and a source of atmospheric CO2. Forests absorb carbon through photosynthesis, but emit carbon through decomposition and when trees are burned due to anthropogenic and natural causes. Managing forests in order to retain and increase their stored carbon will help to reduce the rate of increase in atmospheric CO, and stabilize atmospheric concentrations. Even though some degraded lands are unsuitable for forestry, there is considerable potential for mitigation through improved management of forest lands for carbon conservation, storage and substitution, in balance with other objectives. This section describes national forest practices and measures and international projects and programmes that may be successfully pursued to achieve this goal.20

Forests currently cover about 3.4 Gha worldwide, with 52% of the forests in the low latitudes (approximately 0-25°N and °S latitude). 30% in the high latitudes (approximately 50-75°N and S latitude), and 18% in the mid-latitudes (approximately 25-50°N and °S latitude) (SAR II, 24.2.1). The world's forests store large quantities of carbon, with an estimated 330 Gt C in live and dead above- and below-ground vegetation, and 660 Gt C in soil (mineral soil plus organic horizon) (SAR II, 24.2.2). An unknown quantity of carbon also is stored in products such as wood products, buildings, furniture and paper.

Forest management practices that can restrain the rate of increase in atmospheric CO2 can be grouped into three categories: (i) management for carbon conservation; (ii) management for carbon sequestration and storage; and (iii) management for carbon substitution. Conservation practices include options such as controlling deforestation, protecting forests in reserves, changing harvesting regimes, and controlling other anthropogenic disturbances, such as fire and pest outbreaks. Sequestration and storage practices include expanding forest ecosystems by increasing the area and/or biomass and soil carbon density of natural and plantation forests, and increasing storage in durable wood products. Substitution practices aim at increasing the transfer of forest biomass carbon into products rather than using fossil fuel-based energy and products, cement-based products and other non-wood building materials.

The potential land area available for the implementation of forest management options for carbon conservation and sequestration is a function of the technical suitability of the land to grow trees and the actual availability as constrained by socioeconomic circumstances. The literature reviewed for the SAR (SAR II, 24.4.2.2) suggests that globally 700 Mha of land might be available for carbon conservation and sequestration (345 Mha for plantations and forestry, 138 Mha for slowed tropical deforestation, and 217 Mha for natural and assisted regeneration). Table 14 provides an estimate of global potential to conserve and sequester carbon, based on the above studies. The tropics have the potential to conserve and sequester the largest quantity of carbon (80% of the total potential), followed by the temperate (17%) and the boreal zones (3%). Natural and assisted regeneration and slowing deforestation account for more than half of the amount in the tropics. Forestation and agroforestry contribute the remaining tropical sink, and without these efforts regeneration and slowing deforestation would be highly unlikely.

Scenarios show that annual rates of carbon conservation and sequestration from all of the practices mentioned increase over time (SAR II, 24.4.2.2). Carbon savings from slowed deforestation and regeneration initially are the highest, but from 2020 onwards plantations sequester practically identical amounts as they reach maximum carbon accretion (see Figure 3). On a global scale, forests turn from a global source to a sink by about 2010, as tropical deforestation is offset by carbon conserved and sequestered in all zones.

Using the mean cost of establishment or first costs for individual options by latitudinal region, the cumulative cost (undiscounted) for conserving and sequestering the quantity of carbon shown in Table 14 ranges from about $250-300 billion at an average unit cost ranging from $3.7-4.6h C (SAR II, 24.5.4). Average unit cost decreases with more carbon conserved by slowing deforestation and assisting regeneration, as these are the lowest cost options. Assuming an annual discount rate of 3%, these costs fall to $77-99 billion and the average unit cost falls to $1.2-1.4/t C. Land costs and the costs of establishing infrastructure, protective fencing, education and training are not included in these cost estimates.

While the uncertainty in the above estimates is likely to be high, the trends across options and latitudes appear to be sound. The factors causing uncertainty are the estimated land availability for forestation projects and regeneration programmes, the rate at which tropical deforestation can actually be reduced, and the

"This section is based on SAR II, Chapter 24, Management of Forests for Mitigation of Greenhouse Gas Emissions (Lead Authors: S. Brown, J. Sathaye, M. Cannell and P. Kauppi). 20Mitigation technologies, policies and measures to reduce GHG emissions from grasslands, deserts and tundra are still in their infancy, and mitigation options in these sectors have yet to be evaluated in depth; hence, these are not addressed in this report.

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causing deforestation in much of the tropics (SAR II, 24.3.1.1). In Brazil, on the other hand, wealthier investors are major agents of deforestation, clearing land for cattle ranches that often derive part of their financial attractiveness from land speculation.

Both forest-related and non-forest measures and policies have contributed to deforestation. These include short-duration contracts that specify annually harvested amounts and poor harvesting methods, which encourage contractors to log without considering the concession's sustainability. Royalty structures that provide the government with too little revenue to permit reforestation adequate for arresting forest degradation after harvesting also lead to deforestation. Non-forest policies that lead to direct physical intrusion of natural forests are another prime cause of deforestation. These include land tenure policies that assign property rights to private individuals on the basis of "improvement" through deforestation, settlement programmes, investments promoting dams and mining, and tax credits or deductions for cattle ranching.

Table 15 shows the measures whose successful implementation would slow deforestation and assist regeneration of biomass. Each of these measures will conserve biomass, which is likely to have a high carbon density, and will maintain or improve the current biodiversity. soil and watershed benefits. The capital costs of these measures are low, except in the case of recycled wood, where the capital cost depends on the product being recycled. The first two measures are likely to reduce sectoral (agricultural) employment as deforestation is curtailed. If the subsidies are gainfully invested, they have the potential to create jobs

C Sequestered or Conserved (MU/yr)

elsewhere in the economy to offset this loss. Sustainable forest management has the potential to create economic activity and employment on a long-term basis. The implementation of forest conservation legislation requires strong political support and may incur a high administrative burden. Removing subsidies may run into strong opposition from vested interests. Jointly implemented projects have been slow to take off as the perceived transaction costs are high and financing is difficult to obtain when carbon sequestration is the main benefit. Although sustainable forest management is politically attractive, its implementation requires local participation, the establishment of land tenure and rights, addressing gender and equity issues, and the development of institutional mechanisms to value scarcity; the combination of these factors may incur high administrative costs.

Although reducing deforestation rates in the tropics may appear to be difficult, the potential for significant reduction is

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high, and there are countries, such as Brazil, India and Thailand, where governments have adopted explicit measures and policies to halt further deforestation (SAR II, 24.3.1.1). For instance, in June 1991, the Brazilian government issued a decree (No. 151) suspending the granting of fiscal incentives to new ranching projects in Amazonian forest areas in order to further decrease the annual rate of deforestation (which, as a consequence of economic recession, had reduced to 1.1 Mha for 1990-91 from 2 Mha/yr during 1978-88). The long-term impact of this decree is not yet known, but additional measures could be applied if necessary.

In addition to national measures, protection projects supported by foreign governments, non-governmental organizations and private companies are being formed to arrest deforestation and conserve and/or sequester carbon. The Rio Bravo Preservation and Forest Management Project in Belize, which has been

C Sequestered or Conserved (Gt/yr)

Year

2.5.

-Slow Defor/Regen (d)

-Agroforestry

Forestation

2.01

Total

1.5

C Sequestered or Conserved (Gt/yr)

1.0t

0.5t

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