Carbon Sequestration in Agroecosystems 16 August 2001

Deforestation, mainly in the tropics, averaging more than 13 million hectares (ha) per year during 1980 to 1995 (1), was responsible for 20% (2) to 25% of global, anthropogenic green house gas emissions during the 1990s (3). In absence of mitigation policies, the probability interval for 1990 to 2100 warming is 1.70 to 4.90 degrees Celsius (4), forcing us to find ways to reduce emissions (5). Now that the inclusion of Land Use, Land-Use Change and Forestry (LULUCF) as a credit-earning climate change mitigation option has been taken positively in favor of the afforestation and reforestation for the first 5-year commitment of the Kyoto Protocol (2008-2012) (6), it may be useful for nations to invest in actions that not only have the potential to sequester carbon but also to provide livelihood security to poor people in developing countries, help reduce the rate of deforestation, and contribute to sustainability. Agroforestry and trees outside forests offer an immediate option. Such areas indeed may be acting as the "missing sinks."

This is particularly important because the Clean Development Mechanism will allow afforestation and reforestation projects but exclude all other project types, including those addressing tropical deforestation. This may provide some crediting opportunities for agrofrestry projects, depending on how the rules are written. Trees outside forests in agroecosystems are an important resource providing products and services to society (7). For example, India is estimated to have between 14,224 million (8) and 24,602 million such trees (9), spread over an equivalent area of 17 million ha (10), annually contributing to 98 million tonnes (49% of total 201 million tonnes) of fuel wood, and 31 million cubic meters (out of 64 million cubic meters) of timber requirement in the country (11). This also brings income and well- being to those who practice tree-growing.

Such systems include a variety of local forest management practices (12) where sometimes trees may be retained for up to 300 years (13). The amount of time a carbon sink is retained is an important consideration for designing strategies to manage carbon storage (14). Agroforestry encompasses a wide variety of practices, including trees on farm boundaries, trees grown in close association with village rainwater harvesting ponds, crop-fallow rotations, a variety of agroforests, silvopastoral systems, and trees in urban settlements (15). Agroforestry is practiced globally, but it is widespread in the tropics. Approximately 1.2 billion people (20% of the world’s population) depend directly on agroforestry products and services in developing countries (16). The practitioners are also among the world’s poorest.

Agroforestry practices have the potential to store carbon and remove atmospheric carbon dioxide through augmented growth of trees and shrubs. It has been found promising for carbon sequestration in India (17), Mexico (18), the former Soviet Union (19), Canada (20), and sub-Saharan Africa (21) among others. It also has strong implications for sustainable development because of the interconnection with food production, rural poverty, and associated consequences for the environment. Agroforestry may provide a viable combination of carbon storage with minimal effects on food production. Policies that promote agroforestry will help increase the carbon density of sites relative to traditional agriculture, thereby providing climate change mitigation benefits (3).

For example, agricultural activities occurring on approximately half of the land in the contiguous U.S. provide much of the opportunity to store carbon through afforestation on farms and ranches (22). Carbon sequestration in Indian agroforests varies from 19.56 tonnes of carbon per ha per year (tC ha-1yr-1) in north Indian State of UP (17) to a carbon pool of 23.46 to 47.36 tC ha-1 above and below ground in tree-bearing arid agroecosystems of Rajasthan. The average sequestration potential in agroforestry has been estimated to be 25 tC ha-1 over 96 million ha of land in India, and 6 to 15 tC ha-1 over 75.9 million ha in China (23). Estimates for global potential for mitigation action through improved management are between 400 million ha in agroforestry and 1300 million ha in croplands (3) to a gross 1895 million ha in Asia, Africa, and Latin America (24).

In general, agroforestry can sequester carbon at time-averaged rates of 0.2 to 3.1 tC ha–1 yr-1(3). In temperate areas, the potential carbon storage with agroforestry ranges from 15 to 198 tC ha-1 (25), with a modal value of 34 tC ha-1 (3, 26). Estimates indicate that agroforestry can sequester 7 GtC between 1995 and 2050 globally at a total cost of US$ 30 billion (23), but these estimates are conservative in view of the area, observed rates, and gaps in our understanding. Better estimates can only be known after country-to-country studies become available. The associated impacts of agroforestry include helping to attain food security and secure land tenure in developing countries, increasing farm income, restoring and maintaining above-ground and below-ground biodiversity (including corridors between protected forests), serving as CH4 sinks, maintaining watershed hydrology, and decreasing soil erosion (3).

Agroforestry offers a cost-effective option available in developing countries, such as India, that have large potential. The cost of mitigation in the case of agroforestry may be between US$ 1.6/tC in India and US$ 16.3/tC in China. However, rates are often below US$ 6/tC, making tree-growing a cost-effective option (23).

Agroforestry can also mitigate the demand of wood globally thereby reducing pressure on unmanaged old-growth or mature secondary forests. Intensive harvest of mature forests and/or conversion of mature forests to younger forest stands typically leads to significant carbon losses (27). Agroforestry systems have less biodiversity compared with forests, but they can also act as an effective buffer to deforestation and conversion of forest lands to other land uses, which threaten forests (28). Trees in agroecosystems also support threatened cavity nesting birds and offer forage and habitat to many species of birds (29). It also leads to a more diversified and sustainable production system than many treeless farming alternatives and provides increased social, economic, and environmental benefits for land users at all levels (3). If sustainable small-farm agriculture in developing countries is beneficial to farmers, it can contribute to future food security (30).

Agroforestry systems can be better than other land uses at the global, regional, watershed, and farm scales because they optimize food production, poverty alleviation, and environmental conservation (3). For instance, promotion of species used in the woodcarving industry has three advantages: it facilitates long term locking-up of carbon in carved wood coupled with the creation of new sequestration potential through intensified tree-growing; supports local knowledge on woodcarving and tree-growing, thereby strengthening livelihood security; and helps the trade and industry. These processes are expected to lead to the flow of benefits of globalization to those affected most by it. The unique combination of potential benefits to individual farmers at a local level and environmental benefits at a global level make agroforestry a suitable option.

Existing trees in agroecosystems may be contributing to substantial sequestration of carbon (8). Some studies have argued that emission rates of CO2 from the combustion of fossil fuel have increased almost 40% in the past 20 years, but the amount of CO2 accumulating in the atmosphere has remained the same or even declined slightly (31). This may not be accepted in light of long-term data collected at Mauna Loa mountains in Hawaii showing a steady increase in atmospheric CO2 mean concentration of approximately 316 parts per million by volume (ppmv) in 1958 to approximately 369 ppmv in 1998 (31a). Whatever the case, it has been suggested that much of this carbon has gone into the organic matter of forests that is not often reported in forest inventories (31). For example, more than 75% of the carbon sequestered in the United States is found in organic matter that is not inventoried (32). Agroforestry could as well be the missing sinks.

It can be suggested that forest organic matter is not the only place to look for missing carbon and that some of this missing carbon may also have gone into the missing sinks—-the tree-bearing farmlands—-globally. Support for this inference may be seen in recent findings (33) that Asia seems to be “another place to look for forest carbon sinks” (31). Additionally, 1400 million ha of croplands and agroecosystems may be providing ecosystem services worth US$ 92 ha-1 yr-1 as pollination, biological control, and food production amounting to a total of US$ 128 billion per year at 1994 prices (34). Agroecosystems are also an essential component of developmental intervention for rural livelihood in developing countries (35, 36).

Negotiators will meet at Marrakech in October 2001 to decide modalities for afforestation and reforestation projects under Article 12 of the Kyoto Protocol in the first commitment period, taking into account the issues of non-permanence, additionality, leakage, uncertainties, and socio -economic and environmental impacts (37). Adoption of rules and modalities should make sure to provide crediting for reforestation/afforestation projects that create agroforestry systems.

Asia is also rich in agroforestry and local forest management practices. The obvious next step is the establishment of clear policies and programs globally to sustain the existing agroforest carbon pool, extend and enhance the productivity of the existing pool, establish new pools, and lock up carbon for the long-term in wood products. There is a need to support local forest management practices through the development of suitable policies, assisted by robust country-wide scientific studies aimed at a better understanding about the potential of agroforests for climate change mitigation and human well-being.

References and Notes

1. Food and Agriculture Organization (FAO), State of the World's Forests (FAO, United Nations, Rome, Italy, 1997).

2. Wulf Killmann, Forestry and Climate Change after CoP6. FAO Advisory Committee on Paper and Wood Products, Food and Agriculture Organization (FAO, United Nations, Rome Italy, 2001).

3. R. T. Watson et al., Land Use, Land-Use Change and Forestry (IPCC Special Report, Cambridge Univ. Press, Cambridge, 2000), 388 pp. Available at www.grida.no/climate/ipcc/land_use/index.htm. See also references cited therein.

4. T.M.L. Wigley, S.C.B. Raper, Science 293, 451 (2001).

5. R. Bonnie et al., Science 288, 1763 (2000).

6. UNFCC, Decision 5/CP.6: Implementation of the Buenos Aires Plan of Action, (2001) Available at http://www.unfcc.int/cop6_2/documents/dec5cp6uneditedvers.pdf

7. C. Kleinn, Unasylva 200, 3 (2000).

8. N.H. Ravindranath, D.O. Hall, Biomass, Energy and Environment—a Developing Country Perspective from India. (Oxford University Press, New York, NY, USA, 1995).

9. Ram Prasad et al., Trees Outside Forests in India: A National Assessment (Indian Institute of Forest Management, Bhopal, India, 2000)

10. GOI, National Forestry Action Programme. Government of India, Ministry of Environment and Forests, New Delhi. vol. 1 & 2, and Summary (1999).

11. S.N. Rai, S.K. Chakrabarti, Indian Forester 127, 263 (2001).

12. D. N. Pandey, Ethnoforestry: Local Knowledge for Sustainable Forestry and Livelihood Security (Himanshu/AFN, New Delhi, 1998); D.N. Pandey, Beyond Vanishing Woods: Participatory Survival Options for Wildlife, Forests and People (Himanshu/CSD, New Delhi, 2ed. pp. 222, 1996).

13. D.N. Pandey, Indian Forester 118, 305 (1992) and Indian Forester 119, 521 (1993).

14. Inez Fung, Science 290, 1313 (2000).

15. P. Huxley, Tropical Agroforestry (Blackwell Science Publishers, London, United Kingdom, 1999).

16. R.R.B. Leakey, P.A. Sanchez, Agroforestry Today 9(3), 4 (1997).

17. T.P. Singh et al., Indian Forester 126,1257 (2000).

18. Ben H.J.De Jong et al., Mitigation and Adaptation Strategies for Global Change 2, 231 (1997).

19. T.P. Kolchugina, T.S. Vinson, Mitigation and Adaptation Strategies for Global Change 1,197 (1996).

20. G. Stinson, B. Freedman, Mitigation and Adaptation Strategies for Global Change 6, 1 (2001).

21. J.D. Unruh et al., Climate Research, 3, 39 (1993)

22. NAC (United States Department of Agriculture National Agroforestry Center). Working Trees for Carbon Cycle Balance/Agroforestry: Using trees and shrubs to produce social, economic, and conservation benefits. (Gary Kuhn, USDA NAC East Campus - UNL, Lincoln, 2000) available at http://www.unl.edu/nac

23. J.A. Sathaye, N.H. Ravindranath, Annu. Rev. Energy Environ 23, 387 (1998).

24. J.T. Houghton et al., Global Biogeochem. Cycles 7, 305.

25. R.K. Dixon et al., Climate Change 30, 1 (1994).

26. R.K. Dixon, et al., Global Environmental Change 3, 159 (1993).

27. Ernst-Detlef Schulze et al., Science 289, 2058 (2000).

28. Ian R. Noble, Rodolfo Dirzo, Science 277, 522 (1997).

29. D.N. Pandey, D. Mohan, J. Bombay nat. Hist Soc. 90, 58 (1993); D.N. Pandey, J. Bombay nat. 88, 285 (1991) and 88, 458 (1991).

30. I. Serageldin, Science 285, 387 (1999).

31. S.C. Wofsy, Science 292, 2261 (2001).

31a. UNEP/GRID-Arendal, CO2 Concentration in the atmosphere: Mauna Loa Curve (2001) available at http://www.grida.no/climate/vital/06.htm

32. S.W. Pacala et al., Science 292 2316 (2001).

33. J. Fang et al., Science 292, 2320 (2001).

34. R. Costanza et al., Nature 387, 253 (1997).

35. A.B. Mathur, D.N. Pandey, J. Soc. Ind. For. 32 (3), 9 (1994).

36. D.S. Ravindran, T.H. Thomas, International Forestry Review 2, 182 (2000).

37. UNFCCC/CP/2001/L.11 Draft Decision CP.6 (2001) available at http://www.unfccc.int/resource/docs/cop6secpart/l11.pdf

38. I am grateful for the valuable comments on the draft by Robert Bonnie and D.S. Ravindran. Support of the IIFM, Bhopal is acknowledged.

Deep Narayan Pandey,
Indian Forest Service
Indian Institute of Forest Management, Bhopal, India-462003

Send dEbate response to journal:
Re: Carbon Sequestration in Agroecosystems

E-mail Deep Narayan Pandey:
dnpandey@vsnl.com