Many silvicultural and forest management practices have been reported to enhance carbon mitigation (Lunnan et al., 1991; Hoen and Solberg, 1994; Karjalainen, 1996; Row, 1996; Binkley et al., 1997; Price et al. 1998; Birdsey et al., 2000; Fearnside, 1999; Anonymous, 1999; Nabuurs et al., 2000). Measures suggested for forests include: protecting against fires; protecting from disease, pests, insects, and other herbivores; changing rotations; controlling stand density; enhancing available nutrients; controlling the water table; selecting useful species and genotypes; using biotechnology; reducing regeneration delays; selecting appropriate harvest methods such as reduced-impact logging; managing logging residues; recycling wood products; increasing the efficiency with which forest products are manufactured and used; and establishing, maintaining, and managing reserves.

Sampson et al. (2000) provide an overview of the potential impacts of some different management alternatives on carbon mitigation, and examine both additional benefits and some possible unintended, negative effects of these practices. They estimate that 10% of the global forest area could be technically available by the year 2010, and that the global potential of forest management practices could be 0.17GtC/yr. These opportunities rise to 50% of the global forest area and 0.7GtC/yr by the year 2040. Sampson et al. (2000) emphasize win-win situations, but also indicate the low level of certainty associated with their estimates and the possibility for certain negative impacts.

Nabuurs et al. (2000) also estimate the potential of a broad range of forest-related activities (including protection from natural disturbance, improved silviculture, savannah thickening, restoration of degraded lands, and management of forest products) at 0.6GtC/yr over six regions in the temperate and boreal zone (Canada, USA, Australia, Iceland, Japan, and EU, Figure 4.7). According to their estimates, alternative forest management for C sequestration is technically feasible on 10% (on average) of the forest area in each region examined. Figure 4.8 shows that the relative importance of the different practices for the various regions depends on the current situation in the respective regions.

Forest management and protection offer high mitigation potential in some countries. For example, additional pools of 40-160tC/ha and 215tC/ha may be possible in Cameroon and the Philippines, respectively (Sathaye and Ravindranath, 1998). Afforestation or plantation forest options have the potential to increase carbon stocks by 70–100tC/ha in many places, and the potentials for some commercial plantations may be even higher: 165tC/ha for timber estates in Indonesia, 120tC/ha for timber forestry in India, and 236tC/ha for long rotation forestry in the Philippines (Sathaye and Ravindranath, 1998). The suggested opportunities for mitigation potential in 12 developing countries are summarized in Table 4.3.

The study of Sathaye and Ravindranath (1998) suggests that, in 10 tropical and temperate countries in Asia, about 300Mha may be available for mitigation options: 40Mha for conservation, protection, and management; 79Mha of degraded forest land for regeneration; and 181Mha of degraded land for plantation forestry and, hence, for C sequestration (Sathaye and Ravindranath, 1998). A further 172Mha was estimated to be available in these countries for agroforestry. These estimates are much larger than those in IPCC (1996) (Table 4.4).

Table 4.4: Land categories and extent of availability for mitigation in selected developing countries (Sathaye and Ravindranath, 1998)
Country	Forest land for	Degraded	Degraded land	Agroforestry	Others	Total	Area under
	conservation,	forest land	for plantation			geographic	forests
	protection, and	for regeneration	forestry			area
	management
	(Mha)	(Mha)	(Mha)	(Mha)	(Mha)	(Mha)	(Mha)
Asia
China		19.2	105.2	75.9		932.6	134.0
India		36.9	41.3	96.0		329.0	.63.3
Indonesia			30.5			193.0	144.7
Mongolia		2.4	1.6			156.6	17.5
Myanmar	3.3	6.9				65.8	49.3
Pakistan	0.5	0.3	2.6	1.2		77.1	3.7
Philippines	6.6	2.5			0.60	29.8	6.5
South Korea	0.7	0.3			0.05	9.9	6.5
Thailand	17.8	4.4				51.1	14.0
Vietnam	10.5	6.0			2.50	32.5	19.0
Total	39.4	78.9	181.2	171.9	3.15	1877.4	458.5
Africa
Cameroon	1.6		7.3	1.6		46.0	36.0
Ghana	0.9		0.3	2.5		23.0	18.0
Total	2.5	0	7.6	4.1	0	69.0	54.0
Total (12 countries)	41.9	78.9	188.8	176	3.15	1946.4	512.5

Current estimates suggest that the cumulative C mitigation potential of forests in 10 Asian countries is about 26.5GtC, suggesting that the SAR estimates for the tropical region were conservative. China (9.7GtC) and India (8.7GtC) have particularly large mitigation potentials in the forestry sector (Sathaye and Ravindranath, 1998).

Latin America, which accounts for 51% of the global area of tropical forests (FAO, 1997), has an estimated mitigation potential of at least 9.7GtC, an estimate based on analyses of Mexico, Venezuela, and partly Brazil (Table 4.5). This total includes native forest management, protected areas, commercial plantations, agroforestry, and restoration plantations. The technical potential C mitigation in forestry is estimated at about 4.8GtC for Mexico, 1.4GtC for Venezuela, and 3.5GtC for Brazil (Da Motta et al., 1999, Table 4.5). The feasible mitigation potential, which is largely constrained by land tenure policies and socio-economic pressures (land availability), is, however, often much lower than this technical potential. The feasible socio-economic mitigation potential is about 50% less than the technical potential in Mexico and about 44% lower than the technical potential in India (Ravindranath and Somashekar, 1995).

Deforestation in the Brazilian Amazon is a significant source of CO₂ and, with 90% of the originally forested area still uncleared, Brazil remains a large potential source of future emissions. The deforestation rate in Amazonia was estimated to be 1.38 million ha/yr in 1990, corresponding to an emission of 251MtC/yr (Fearnside, 1997). The rate of deforestation has increased in recent years, to 2.91Mha/yr in 1995 and 1.82Mha/yr in 1996 (Fearnside, 1998). Reducing the deforestation rate by 50% would conserve 125MtC/yr. Thus, Brazil alone offers a large potential for mitigation through slowing of deforestation.

What is the permanence of C sequestered by forest management activities? Clearly, tree plantations that are harvested and not re-established do not contribute to long-term carbon sequestration, though they may reduce atmospheric C in the short term. But, if a new forest is maintained so that harvest equals net growth, the forest can both be a source of wood products and still retain the captured C. In other words, the sequestration phase may be finite, lasting only a few decades, but the conservation phase need not be finite. Although there is an exchange of carbon between the atmosphere and the biomass, a considerable pool of carbon can be permanently stored in the steady-state biomass while wood products continue to be produced. This C pool remains withdrawn from the atmosphere as long as the forest exists. The substitution phase, which begins at the onset of the first harvest, can be sustained. Each timber crop, in a cumulative manner, can substitute for fossil-fuel resources. The forest thus offers a sustainable alternative to the unsustainable use of fossil-fuel resources (Schlamadinger and Marland, 1996).

Land owners are unlikely to manage their forest resources for C sequestration alone. In the absence of financial incentives, any C sequestration will likely be incidental, or have the role of a by-product in the management of forests to produce valued goods and services (ITTA, 1983, 1994). In the tropical biome, the optimal mix of management strategies will likely reflect a balance between various forest management systems and agricultural production. Existing policies for forest and agricultural land management, however, do not yet reflect economic incentives for C management and probably are not optimal (see for example Poore et al., 1989).

The effectiveness of various strategies for C sequestration will depend on the initial status of the forest ecosystems. For lands without tree cover, afforestation permits large C gains per hectare (Dyson, 1977; Sedjo and Solomon, 1989). Industrial plantation forests are already being created on a large scale and expansion of this area for C sequestration is possible (Sedjo and Sohngen, 2000). The establishment of forest plantations is generally the most reliable silvicultural method for afforestation, reforestation, and sustainable regeneration (regeneration soon after cutting). Plantation establishment can enhance productivity if desired species are planted on suitable sites. Plantations can reduce the pressures to degrade natural forests (Sedjo and Botkin, 1997). However, following the harvest of a mature or old-growth forest, the land can remain a source of carbon for many decades, even when it is regenerated (Hoen and Solberg, 1994; Cohen et al., 1996; Schlamadinger and Marland, 1996; Bhatti et al., 2001). Therefore, for primary and mature forests, conserving and protecting the existing C pools is often the only mitigation option that yields near-term benefits.

Because of the diversity in the current global forest status and socio-economic situation, the optimal mix of mitigation strategies will vary with country and region, in both the tropics and the non-tropics. For many countries, slowing or halting deforestation is a major opportunity for mitigation (e.g., Brazil: Fearnside, 1998, and Mexico: Masera, 1995). In countries such as India, where deforestation rates have declined to marginal levels, afforestation and reforestation in the degraded forest and non-forest lands offer large mitigation opportunities (Ravindranath and Hall, 1995). Ravindranath and Hall (1995) have shown the potential of using this degraded land and small biomass gasifiers to sustainably produce electricity from woody biomass and displace 40 million tonnes of C annually. In Africa an important opportunity for mitigation is in conserving wood fuel and charcoal through improved efficiencies of stoves and charcoal kilns (Makundi, 1998). The selection of mitigation strategies or projects in tropical countries, particularly, will be determined by economic development priorities, changing pressures on land use, and resource constraints. In many industrialized countries, adjusting forest management regimes and material flows in the forest products sector (including substitution) appears most promising (Hoen and Solberg, 1994; Binkley et al., 1997).

To quantify accurately the effects of changes in forest management on the net transfer of C to the atmosphere, the whole system could be considered (see Box. 4.1). Many earlier studies focused on the immediate results of forest management measures, e.g. the higher biomass growth rate following a silvicultural treatment or the protected stock of C if wildfire or logging is prevented. Global assessments based on these studies (e.g., Dixon et al., 1994; Brown et al., 1996b) have limitations. Estimates, in terms of tC/ha or tC/ha/yr, leave unanswered the critical questions of the timing, security, and sustainability of these effects. Also, recent, more comprehensive studies indicate the importance of complete accounting for all the C flows in and out of the system and the analysis of long-term patterns. For example, Schlamadinger and Marland (1996) showed that the positive effect of short-rotation plantations for fossil fuel substitution is less than implied by the simple substitution of fossil fuels, because of the continued input of fossil fuels needed to operate the system. While the limitations of earlier studies are now evident, data for comprehensive analysis at the global scale are not yet available. This, in part, explains why global-level estimates of the potential for C mitigation in forestry remain unchanged from those in SAR.

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