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

96World Agroforestry into the Futureamong living organisms from all sources,including, inter alia, terrestrial, marine andother aquatic ecosystems, and the ecologicalcomplexes of which they are part; thisincludes diversity within species, betweenspecies, and of ecosystems.” Spatial andecological scales are therefore fundamentalconcepts in biodiversity studies. TheUNCBD further defines agrobiodiversity asbiodiversity that is important for agriculturalproduction, including crop and livestockgenetic diversity, wild biodiversity closelyassociated with domesticated species, andother wild biodiversity sharing the resources.‘Wild biodiversity’ is biodiversity that hasnot been domesticated, while ‘domestication’is the dynamic process of how humansselect, improve, manage, propagate andintegrate trees or other plants into land usesystems. While ICRAF and its partners haveconducted a great deal of work on belowgroundbiodiversity (e.g. van Noordwijk etal. 2004), we concentrate here on abovegroundbiodiversity at the landscape scale,explicitly focusing on the links between theplanting and management of trees by farmersand biodiversity in the landscape.Several definitions of the term ‘agroforestry’are used in science and practice. Leakey’s(1996) definition is used most frequently:“a dynamic, ecologically based, naturalresource management system that, throughthe integration of trees on farms and in thelandscape, diversifies and sustains productionfor increased social, economic andecological benefits.” Three aspects of thisdefinition are important for the biodiversityvalue of agroforestry. Firstly, agroforestryinvolves the deliberate integration of treeswith farms and landscapes, which mayhave direct and indirect effects on farm andlandscape biodiversity. Secondly, there aretrade-offs and complementarities betweenthe social, economic, ecological and biodiversitybenefits of agroforestry comparedto other land use systems; indeed, thequantification of trade-offs has been at theheart of the research agenda of the Alternativesto Slash and Burn (ASB) Programmecoordinated by ICRAF (Tomich et al. 2001).Thirdly, while some agroforestry practicesin certain circumstances contribute greatlyto diversification and sustainability, thereare other circumstances where it contributesvery little.Propositions aboutrelationships betweenagroforestry and biodiversityA number of recently completed reviewpapers suggest ways in which agroforestrycontributes to the conservation and protectionof biodiversity, including that of bothwild species and species more directlyrelated to agricultural production (Boffa1999; Buck et al. 2004; Cunningham et al.2002; McNeely 2004; McNeely and Scherr2003; Schroth et al. 2004a; van Noordwijket al. 1997). These and other studies suggestfour key relationships between agroforestryand landscape biodiversity.1. Agroforestry farmers and systemsas promoters of plant diversityProposition: While modifying naturalvegetation for their productive use, farmersdevelop and maintain agroforestrysystems that make substantial contributionsto biodiversity in multi-functionallandscapes.The proposition that agroforestry will resultin ‘substantial contributions’ to biodiversityis supported by a good deal of evidenceregarding the diversity of tree and vascularplant species across a variety of landscapes,including those containing agroforestrysystems. There are important caveatsto the proposition, however: i) there arelarge differences in the biodiversity valueof different agroforestry systems; ii) some ofthe more diverse agroforestry systems maybecome less diverse under high levels ofpopulation pressure; and iii) the commoditiesthat underpin many of the most diverseagroforestry systems are subject to fluctuationsand declines in profitability whenadopted on a large scale.The ASB programme has evaluated the biodiversityassociated with a range of typicalland use types, including agroforestry, thatare found at the frontiers of tropical forestsin Southeast Asia, the Congo Basin, and theAmazon Basin. Methods used and resultsgenerated by this comprehensive set ofstudies are available on the ASB web page(www.asb.cgiar.org). Summary results arealso presented in Tomich et al. (1998) andTomich et al. (2001). In general the resultsshow that multistrata agroforestry systemscontain an intermediate level of plant biodiversitythat lies between primary forestsand monocrop perennials or field crops.For example, Murdiyarso et al. (2002) comparedthe number of plant species found indifferent types of land use in the Jambi areaof central Sumatra. They found that continuouslycultivated cassava had 15 speciesper 1.5-hectare plot, oil palm plantationshad 25 species per plot, rubber agroforestshad 90 species per plot, while primary forestshad 120 species per plot.Gillison et al. (2004) found that complexagroforestry systems and shade-growncoffee both had much higher levels ofbiodiversity than simple sun-grown coffee,although all coffee systems had lower biodiversitythan primary or secondary forests.