Sustainable Land Management for Mitigating Climate Change

Table 14. Experimentally measured rate of soil carbon sequestration with adoption of various sustainable land management options (Lal, 2008).

SLM Option	Region	Rate (kg C/ha/yr)
I. Cropland soils
(i) Conservation tillage	North America	200-1200
	South America	300-600
	Australia	100-1000
(ii) Rotations	North America	200-300
(iii) Nutrient management	North America	300-500
	South Asia	500-1000
	Tropics	100-200
(iv) Intensive farming	North America	500-1000
	Europe	500-1000
II. Grazing land soils
(i) Rangeland management	North America	20-500
(ii) Pasture management	North America	500-1000
III. Forest land soils
(i) Stand management	Europe	400-500
	North America	600-800
(ii) Afforestation	Europe	500-3000
	Sub-Saharan Africa	100-3000
(iii) Agroforestry	Central America	500-800
IV. Minesoil Reclamation
(i) Afforestation	North America	300-3000
	Pacific	1500-2500

XIII. Desertification Control

77. Desertification is the persistent degradation of dryland ecosystems by variations in climate and human activities (UNEP, 1977, 1990; UNCED, 1992; www.unccd.int; MEA, 2005). Desertification is caused by various social, political, economic, and natural factors which vary from place to place and in time (Mortimore, 1994; Mainguet and da Silva, 1998). In drylands, more people depend on ecosystem services for their basic needs than in any other ecosystem. Yet land degradation in these drylands diminishes biological productivity and directly affects ecosystem services (e.g., food and water, climate regulation, soil conservation, recreation) provided to millions of people. The process of desertification has been studied with regards to its impact on production, income and well being of people (Mendoza, 1990; Blaikie, 1989; Verstaete, 1986; MEA, 2005). The effect of global CC on desertification is complex and not fully understood. However various approaches for combating desertification and mitigating CC are directly linked in many ways thus necessitating synergistic implementation of the United Nations conventions on desertification, climate change and biological diversity (MEA, 2005). It is important to point out that various SLM technologies and practices offer crucial, and in many cases the only, options for combating desertification in many parts of the world. Such practices also provide the best practical options for effective local actions to address climate change.

78. However, the process of desertification is not confined to the drylands of the tropics or economically developing regions alone. It also occurs in developed countries (e.g., USA), high latitude humid ecoregion (e.g., Iceland) and even humid regions (tropical rainforest). It results mainly from land misuse and soil mismanagement. The 2005 Millenium Ecosystem Assessment confirmed that desertification is potentially the most threatening ecosystem change impacting livelihoods of the poor. Land degradation and desertification undermines the long-term development of many nations. The scale of the land degradation challenge calls for sustained and collective action by the international community. But for these efforts to bear sustainable results, the implementation of of measures to combat land degradation and desertification (i.e., UNCCD) must be guided and defined at the country level.

79. Drylands cover 47% of Earth’s land area (Table 15). Because of the harsh climate, these regions are prone to desertification. The problem is exacerbated by marked rainfall seasonality and variability, which determine the pulse of biological activity and NPP. Estimates of the extent of desertification range widely and are highly subjective. UNEP estimated 3.97 Bha in 1977, 3.48 Bha in 1984 and 3.59 Bha in 1992 (UNEP, 1977, 1984a; b, 1992). The land area affected by desertification was estimated at 3.25 Bha by Dregne (1983) and 2.0 Bha by Mabbutt (1984). According to the GLASOD methodology (Oldeman and Van Lynden, 1998), the land area affected by desertification is estimated at 1.14 Bha (Table 16). These estimates are similar to those by UNEP (1991) with reference to degradation of soil and vegetation. In addition, UNEP's (1991) estimates include 2.58 Bha of degraded vegetation on rangelands. Estimates of the current rates of desertification also vary widely, and the annual rate is estimated at 5.8 Mha or 0.13% of drylands in the mid latitudes (Table 17). Eswaran et al. (2001) estimated the land area vulnerable to land degradation and the number of impacted people (Table 18). The area vulnerable to degradation is 4324 Mha (33% of Earth’s land area) and the impacted population is 2.65 billion (46% of the world’s population in 2000). Eswaran and colleagues also estimated land area affected in regions with different population density. Total land area vulnerable to desertification is 1990 Mha for population density of <10 person/km², 1160 Mha for 11-40 persons/km² and 1170 Mha for population density of >41 persons/km² (Table 18). Bai et al. (2008) estimated the global extent of land degradation on the basis of decline in NPP, and reported that 3506 Mha are degraded (23.5% of the land area), and about 1.54 billion (23.9%) people are affected globally (Table 19).

Table 15. The extent of global drylands (recalculated from UNEP, 1992). The climatic classification is based on FAO (1993).
Classification	Land Area (Bha)