The challenge of HIV/AIDS: Where does agroforestry fit in? - World ...

Chapter 13: Opportunities for linking climate change adaptation and mitigation115sub-humid tropics of Togo and Kenya haveshown various degrees of success dependingon location (rainfall and soil type),fallow species, duration of the fallow phaseWetlandrestorationRestoration ofdegraded landsAgroforestryForestmanagementGrazingmanagementRicemanagementCroplandmanagementFigure 1. Carbon (C) sequestration potential (in millions of tonnes per year) of differentland use and management options.Source: IPCC (2000).C stock (Mg ha —1 )3002502001501005000 100 200 300 400 500 600 700Primary forestPotential C sequestration by 2040 (Mt C y —1 )Managedforestand sampling depth; soil organic carbonaccretions through employing improvedfallow were estimated to be between 1.69and 12.46 Mg ha –1 (Table 2).Agroforestry systemsEcosystemsCrops, pasturesand grasslandsFigure 2. Summary of carbon (C) stocks in different ecosystems of the humid tropics. Dataare from the benchmark sites of the Alternatives to Slash and Burn (ASB) Programme of theConsultative Group on International Agricultural Research (CGIAR).Although carbon fluxes in agroforestry systemsare well documented, we have a muchpoorer understanding of the effects of thesepractices on non-carbon dioxide (CO 2)greenhouse gases. In the case of nitrous oxide(N 2O) emissions, much depends on thepresence or absence of legumes in the system.In general, agroforestry systems, whichpromote the use of legumes as fertilizer orshade trees, may increase N 2O emissionscompared to unfertilized systems. Similarly,tree-based systems that encourage the introductionand development of livestockfarming may contribute to increasing methane(CH 4) emissions. While efforts shouldbe made to minimize the emission of thesetrace gases, what ultimately matters in termsof climate change mitigation is how theseemissions compare to the amount of carbonsequestered in agroforestry systems. Forexample, in an improved fallow–maize rotationsystem in Zimbabwe, N 2O emissionswere found to be almost 10 times those ofcontinuous unfertilized maize (Chikowoet al. 2003), but these levels were still extremelylow when compared to the increasein the amount of carbon stored.Enhancing farmer adaptivecapacity through agroforestryAs adaptation emerges as a science, therole of agroforestry in reducing the vulnerabilityof agricultural systems (and the ruralcommunities that depend on them for theirlivelihood) to climate change or climatevariability needs to be assessed more effectively.Rainfall variability is a majorconstraint in the semi-arid regions and tothe upland farms in Southeast Asia that donot have access to irrigation. However,the effects of variable rainfall are oftenexacerbated by local environmental degradation.Therefore, curbing land degradationcan play an important role in mitigatingthe negative impacts of climate change and