CHAPTER 8 Agroforestry for Biodiversity in Farming Systems Roger R. B. Leakey CONTENTS Introduction Sustainable Production Agroforestry Agroforestry and the Diversification of Agroecosystems Development of Multistrata Agroforests Biodiverse Agroecosystems Forest Patches, Biogeographical Islands, and Agroforestry Domestication of Trees for Timber and Nontimber Forest Products Commercialization Tree Domestication in Progress Conclusions References Abstract — Agroforestry can be used to diversify and intensify farming systems through the integration of indigenous trees producing marketable timber and nontim- ber forest products and is described in terms of an agroecological succession, in which climax agroforests are biodiverse, highly productive, and profitable. The role of biodiversity in agroecosystem function is one of the keystones of sustainability. Complex agroforests that combine profitability with biodiversity are presented as a model worthy of expansion. However, little is known ecologically about how best to integrate agroforestry into the landscape, or to what extent agroforestry can be used to link forest patches and expand biogeographical islands. © 1999 by CRC Press LLC. Tree domestication is one way to diversify and intensify agroforestry systems and to make them profitable. A wise domestication strategy for indigenous trees will involve the capture and maximization of intraspecific genetic diversity and so benefit both production and the environment. INTRODUCTION The numbers of plant and animal species on Earth represents only 0.1% of those that have existed since life appeared on this planet, the other 99.9% being already extinct as a result of five episodes of mass extinction over geological time (Leakey and Lewin, 1996) and the current period of extinctions (30,000/year against a background of 0.25/year) arising from our population growth and lifestyle. Land- use changes associated with colonization have been the major cause of these species losses over the last few centuries. Agriculture, which has been described as the “engine of economic growth” because of its powerful role in facilitating and stim- ulating growth of other sectors of the economy (Mellor et al., 1987), started as a subsistence activity 8000 years ago. The early subsistence systems are generally considered to have been sustainable, while large-scale, capital-intensive, modern agriculture has traded innate sustainability for chemical and other inputs and is characterized by deforestation and a decrease in the overall numbers of associated wild plants and animals to favor the growth of the planted crop. Typically, agriculture systems and forestry plantations are monocultures of staple food or tree crops with the almost total disappearance of the biodiversity and spatial complexity of natural ecosystems. Characteristically, these monocultures are also based on the few plant species that have been domesticated (Leakey and Tomich, 1998) and which also have a narrow genetic base. In recent years, these developments have given rise to concerns about deforestation, the loss of biodiversity, and the sustainability of our lifestyle and, particularly, the crucial food production systems that are essential to prevent famine and malnutrition in the tropics. SUSTAINABLE PRODUCTION Many of the means to increased productivity and profitability are now perceived by society as carrying too high a cost in social disruption, human inequity, and environmental degradation. The problem in trying to address this is how to define and quantify sustainability. Izac and Swift (1994) developed an operational frame- work to assess sustainability based on the premise that “a cropping system is sustainable if it has an acceptable level of production of harvestable yield which shows a non-declining trend from cropping cycle to cropping cycle over the long term.” Their framework is based on the assessment of key ecological and economic parameters at the field, farming system, and village/catchment scales and the concept that a sustainable system never reaches threshold levels of irreversibility and that it achieves a sufficient level of economic efficiency and social welfare. One of the © 1999 by CRC Press LLC. requirements identified by Izac and Swift (1994) is that the by-products (soil and water quality, biological diversity, etc.) of agricultural activities must not disrupt the biological functions of the system to the extent that the capacity of the system to absorb these disruptions is surpassed. Sustainability thus involves a symbiosis between the properties of the ecosystem and the management activities that results in nondeclining and relatively stable outcomes. Izac and Swift (1994) consider that the key to this symbiosis lies in the assumed positive relationship of agroecosystem function to biodiversity and com- plexity. Biodiversity therefore is a keystone in sustainability, and its loss has been one of the common outcomes of agricultural intensification (Figure 1). Agroforestry, through the replenishment of soil fertility and the domestication of indigenous trees producing marketable forest products, has been proposed as one way of diversifying and intensifying agroecosystems in a way that is beneficial to the environment and can maintain and perhaps enhance biodiversity (Sanchez and Leakey, 1998; Sanchez et al., 1998). In its Medium Term Plan 1998–2000, the International Centre for Research in Agroforestry (ICRAF, 1997) foresees that agro- forestry can contribute to human welfare and environmental resilience, with improved systems providing: 1. Tree products that both increase food and nutritional security and generate cash income for poverty alleviation and 2. Services that support and enhance ecosystem function (Figure 2). The relevant services of trees are those that increase the crop yields (nitrogen fixation, increased soil organic matter, nutrient cycling, soil conservation, etc.), create environmental resilience (niche diversification, food web complexity, carbon seques- tration, reduced greenhouse gas emissions, etc.), and provide social benefits (bound- ary delineation, shade, etc.). Of these, the least is known about the ways in which trees enhance the environment, although the body of information is increasing (see Ingram, 1990; Swift et al., 1996). AGROFORESTRY Agroforestry, where it has been practiced traditionally, such as in the damar agroforests of Sumatra and Jungle Rubber on Kalimantan (Michon and de Foresta, 1996) and in the home gardens of Sri Lanka (Jacob and Alles, 1987), Nigeria (Okafor and Fernandes, 1987), and Tanzania (Fernandes et al. 1984), is a mixed and often apparently haphazard polyculture of indigenous trees and crops that form a complex, multistrata system somewhat like a natural forest. Interestingly, recent findings in the damar agroforests of Sumatra show that these complex multistrata agroforests contain over 50% of all the regional pool of resident tropical forest birds, most of the mammals, and about 70% of the plants (Table 1). They are also a major source of resins, fruits, and timber for domestic use and for export. Thus, these agroforests are potentially a sustainable resource, a valuable compromise between conservation © 1999 by CRC Press LLC. Figure 1 The impact of agricultural intensification on an agroecosystem. (From Swift, M. J. and Anderson, J. M., 1993. Biodiversity and Ecosystem Function, Schulze, E D. and Mooney, H. A., Eds., Springer-Verlag, Berlin. With permission.) © 1999 by CRC Press LLC. Figure 2 The relationship between the two functions of trees and the three goals of agro- forestry to meet three global challenges. (Modified from ICRAF 1997, Int’l Centre for Research in Agroforestry Medium Term Plan 1998–2000. With permission.) Table 1 Biodiversity in Indonesia Agroforests: Observed Numbers of Species Primary Forest Rubber Agroforest Damar Agroforest Durian Agroforest Rubber Plantation Birds a 179 105 92 69 — Collembola b Leaf litter 20.6 22.8 — — 11.6 Soil 13.7 16.0 — — 8.3 Mammals c —39 46 33 — Trees d 171 92 — — 1 Total plants d 382 266 — — 6 a Thiollay, 1995. b Deharveng, 1992. c Sibuea and Herdimansyah, 1993. d Michon and de Foresta, 1995. © 1999 by CRC Press LLC. of tropical forest biodiversity and profitable use of natural resources, since in addition to their biodiversity these multistrata damar agroforests in Sumatra are financially attractive. Damar resins are utilized by industries in Indonesia or exported worldwide. In 1984, the export market represented one third of the harvested volume, a trade rising from 250 to 400 t/year between 1972 and 1983 (Michon et al., 1998). In 1994, the damar production was expected to reach 10,000 t (Dupain, 1994), at a value of U.S. $300 to 400/t. Of this trade, 80% is met by the damar agroforests. The economic value of the damar trade and its associated activities is of major significance to the villages around Krui. In 1993, the profits from damar production were U.S. $7.2 million from sales, U.S. $2.6 million from added value, and U.S. $1.4 million from wages. To this is added U.S. $0.3 million in profits made by Krui traders (Michon et al., 1998). This analysis excludes the locally consumed products from these agroforests, e.g., fruits, vegetables, spices, fuelwood, timber, palm thatching, rattan, bamboo, fibers, as well as paddy rice. With the exception of plantation crops, many farming systems in the tropics, including traditional subsistence swidden farming, are based on mixtures and are frequently haphazard in their configuration and spacing. In contrast, monocultures are particularly prevalent in countries with temperate climates. It is not clear whether or not the tendency to complexity and random distribution of the components of farming systems in the tropics is a deliberate attempt by farmers in the tropics to mimic the diversity of natural ecosystems in order to minimize risk. In contrast to traditional agroforestry, the recent development of agroforestry as a science by agronomists and foresters has tended to adopt the temperate model and to plant the tree component in lines, regular patterns, or along the contour of sloping land (see review by Cooper et al., 1996). This is especially the case in countries where farm size is large (e.g., Australia), where large areas of countryside are planted in geometric patterns. Modern agroforestry has also tended to be a set of stand-alone technologies, that together form various land-use systems in which trees are sequentially or simulta- neously integrated with crops and/or livestock (Nair, 1989). Recently, however, it has been suggested that agroforestry practices should be successional phases in the development of a productive and complex agroecosystem, akin to the succession of natural ecosystems (Leakey, 1996). In this way, trees producing different products can be used to fill niches in a mosaic of patches in the landscape, making the system ecologically more stable and biologically more diverse. It is anticipated that this diversity would increase with each phase of the agroecological succession. Toward this end, current activities at ICRAF are focusing on the development of agroforestry as “a dynamic, ecologically-based, natural resource management system that, through the integration of trees on farms and in the landscape, diversifies and sustains production for increased social, economic and environmental benefits.” One aspect of this is to determine, through the use of models, the best land-use options for agricultural productivity and biodiversity conservation: the choice between integration or segregation (van Noordwijk et al., 1995b). In parallel with these developments in agroforestry there has also been a move to promote the domestication of indigenous trees, the “Cinderella” trees overlooked © 1999 by CRC Press LLC. by science (Leakey and Newton, 1994a; Leakey and Jaenicke, 1995; Leakey and Izac, 1996). Bringing the new ideas about agroforestry and about domestication together provides one with a new paradigm for sustainable land-use development that focuses on two aspects of biodiversity: 1. Diversifying agroecosystems 2. Capturing and enhancing intraspecific diversity AGROFORESTRY AND THE DIVERSIFICATION OF AGROECOSYSTEMS From past experience, domesticated trees are frequently grown in monocultures, but they could play an important role in species-rich multistrata agroforests (Leakey, 1996b). The development of multistrata systems that include cultivars of domesti- cated trees could increase the profitability of these agroforests. Thus this approach could, it seems, go a long way toward the establishment of land uses that will fulfill the needs of rural and urban populations for food and income, while maintaining much of the biological diversity of forests or rehabilitating degraded ecosystems. Much research will be needed, however, to achieve this and to demonstrate that productivity and profitability are not necessarily environmentally damaging. Evidence already emerging from studies to develop viable alternatives to slash-and-burn agri- culture suggests that the greenhouse gas emissions, especially methane, from areas where sources such as paddy fields are juxtaposed with perennial vegetation are lower than from areas monocropped with rice (van Noordwijk et al., 1995a). However, the successful establishment of trees on cleared sites is known to suffer from changes in the populations and species diversity of symbiotic microflora associated with land clearance (Leakey et al., 1993; Mason and Wilson, 1994), and similar changes prob- ably occur in the beneficial micro- and mesofauna above- and belowground. Evidence exists for the negative effects of site clearance on soil fauna populations (Eggleton et al., 1995) and for the need to restore them to ensure soil fertility. A challenge for agroforestry research is to develop economically and socially acceptable land-use systems that function like undisturbed ecosystems and maintain biodiversity. Could complex multistrata agroforests, like those of Sumatra, be devel- oped in humid West Africa and in Latin America? The answer is almost certainly yes. Indeed, simple indigenous multistrata systems already exist, such as the cocoa farm, and the compound gardens of West Africa (Okafor and Fernandes, 1987), while in the Peruvian Amazon, multistrata agroforests have been found to be an economically attractive system (Table 2). DEVELOPMENT OF MULTISTRATA AGROFORESTS There are plenty of tree species that have traditionally provided local people with their daily needs for the full range of nontimber forest products, which could © 1999 by CRC Press LLC. now be incorporated into agroforestry systems. Table 3 illustrates candidate species for West Africa (see also Okafor and Lamb, 1994; Abbiw, 1990). How can these complex agroforests be further developed in the tropics? Probably three things are required. First, there is the need to identify the species of commercial importance of relevance to local markets. Second, there is a need to develop an entrepreneurial mentality among the community, who have traditionally been subsistence farmers and hunter–gatherers. Third, there is a need to determine how best the tree species may be combined to develop agroforests. The growth of the urban market and the absence of jobs in the urban areas may provide the commercial incentive required. What is probably missing is the demonstration of what is possible, particularly in the areas near urban markets. With such a wide choice of species for the middle and upper strata of multistrata agroforests, clearly research to determine the best combinations and configurations is much needed, but also extremely difficult. There are, therefore, three research approaches that can be taken: 1. The testing of prototype systems (i.e., best-guess combinations), perhaps aimed at market needs, and developed with the help of farmers with some experience of compound gardens; 2. Research to test specific hypotheses aimed at the development of some principles regarding the optimal combinations and/or densities of trees in the different strata, which involves both complementarity of species biologically and in terms of labor demands and market opportunities; 3. Use of random mixtures of the species in unstructured combinations, as would probably be developed by farmers. Research is needed to determine whether or not the apparently random distribution of trees in many existing examples of multistrata systems is indeed random, or whether farmers from experience grow species in certain combinations. Understand- ing this process would be of benefit in assisting attempts to know why multistrata systems evolve differently under different social and ecological conditions and would therefore help to transfer these systems more effectively to new areas. Table 2 Comparison of Net Present Values and Internal Rates of Returns of Production Systems in 1985 and 1991 Prices Using a 15-Year Time Horizon in Yurimaguas, Peru Production Option 1985 Prices 1991 Prices Net Present Value (U.S.$ ha –1 ) Internal Rate of Return (%) Net Present Value (U.S.$ ha –1 ) Internal Rate of Return (%) Multistrata system 6444 219 6727 831 Peach palm 979 35 2061 64 Shifting cultivation 79 7 218 19 Note: Low input and high input continuous cultivation both had negative net present values. From ICRAF, 1994 Annual Report, Nairobi, Kenya, 1995. © 1999 by CRC Press LLC. There are a number of options on how to apply these approaches to the devel- opment of multistrata systems: 1. Enrichment planting within logged or degraded forest; 2. Planting in cleared forest land as a perennial tree alternative to slash-and-burn agriculture; 3. Planting under a plantation of either an upper or middle strata species. Of these options, 1 and 3 have merit environmentally in that the system will be developed more quickly as a demonstration and will not leave the land bare at the establishment phase. On the other hand, option 2, the currently most practical from the perspective of smallholders, is probably the most relevant in terms of developing Table 3 A Sample of the West African Tree/Shrub/Liane Species Appropriate for Growth in Multistrata Agroforests and for Domestication Common Names Mature Height (m) Anthocleista schweinfurthii Ayinda 15–20 Antrocaryon micraster Aprokuma/onzabili 40–50 Baillonella toxisperma Moabi 45–55 Calamus spp. Rattan 35–45 Canarium schweinfurthii Aiele/Africa canarium/incense tree 45–55 Chrysophyllum albidum Star apple 30–40 Cola acuminata Kola nut 15–25 Cola lepidota Monkey kola 10–20 Cola nitida Kola nut 20–30 Coula edulis Coula nut/African walnut 25–35 Dacryodes edulis African plum/Safoutier 15–25 Entandrophragma spp. Sapele/tiama/utile/sipo 50–60 Garcinia kola Bitter kola 20–30 Gnetum africanum Ero 0–10 Irvingia gabonensis Bush mango/andok 20–30 Khaya spp. African mahogany 50–60 Lovoa trichiloides Bibolo/African walnut 40–50 Milicia excelsa Iroko/mvule/odum 45–55 Nauclea diderichii Opepe/kusia/bilinga 35–45 Pentaclethra macrophylla Oil bean tree/Mubala/Ebé 20–30 Raphia hookeri and other spp. Raphia palm 5–15 Ricinodendron heudelotii Groundnut tree/nyangsang/essessang 40–50 Terminalia ivorensis Framiré/Idigbo 45–55 Terminalia superba Fraké/afara/limba 45–55 Tetrapleura tetraptera Prekese/Akpa 20–30 Treculia africana African breadfruit/etoup 20–30 Trichoscypha arborea Anaku 15–25 Triplochiton scleroxylon Ayous/obeche/wawa 55–65 Vernonia amydalina Bitter leaf 0–10 Xylopia aethiopica Spice tree 15–25 From Leakey, R. R. B., Agroforestry Systems, 1998. With permission. © 1999 by CRC Press LLC. multistrata systems. Such systems are both relevant on good soils of land cleared at the forest margin and on already degraded land, perhaps with proximity to urban markets. Because this option is the most relevant practically, it is also probably the one on which the greatest research effort should be concentrated. In all these options, research is especially required to determine the functional groups of species which will do well in the lower strata, where light will be a limiting factor. Currently in Southeast Asia, staple food crops are grown beside the multistrata agroforests, because they are light demanding. This may be the best arrangement, but it is also possible that new crops, or new cultivars of existing crops, could be integrated into multistrata agroforests. BIODIVERSE AGROECOSYSTEMS From the biodiversity viewpoint, there is a difference in agroecosystems between the planned biodiversity and the unplanned, or associated, biodiversity. The latter are all those organisms, above- and belowground, that have found niches to fill among the planted trees and crops. The extent to which unplanned biodiversity occurs in different agroecosystems is not well known or understood, although studies have started to address the effects of a broad spectrum of agricultural practices on wildlife populations (McLaughlin and Mineau, 1995; Perfecto and Snelling, 1995). Swift et al. (1996) have, however, drawn four very different scenarios for the relationships between agricultural intensification and biodiversity (Figure 3), although these may be very scale dependent (e.g., from farm to landscape) and probably also vary depending on the level of biodiversity at the time of planting. Thus, the biodiversity associated with an agroforest planted on recently cleared land at the forest margin, as an alternative to slash-and-burn agriculture, would almost certainly be very different from the same tree/crop mixture planted to rehabilitate already degraded land. There is a need for controlled experiments to determine these relationships between intensification and biodiversity. In addition there is a need to determine the patterns of diversity in different agroforestry systems and their impli- cations for ecological functioning at different scales. There is currently unresolved debate about the functional role of species diversity in ecosystems (Johnson et al., 1996), which makes it difficult to suggest best practices. However, it seems that planned biodiversity should aim at maximizing ecosystem processes (nutrient cycling, production of different products, light requirements, etc.) and structural complexity, rather than increasing the number of species per se. However, species numbers may also impact on function. The few studies in which the diversity of agricultural ecosystems has been manipulated suggest that increases in diversity from 0 to 10 plant species alters ecosystem function, but that there is little effect beyond that point (Schulze and Mooney, 1993). Species also vary in their importance in different food webs, where, once again, scale is important. For example, for a fruit tree species to support a population of monkeys will require a large habitat. A small area of fruit trees may therefore avoid monkey damage and so be preferable for production, but without a large area there may not be a market for the crop. Thus, ecological and economic factors affecting © 1999 by CRC Press LLC. [...]... in Kenya reveals rapidly increasing forest resources, Ambio, 23:390–395 ICRAF, 1995 1994 Annual Report, ICRAF, Nairobi, Kenya ICRAF, 1997 ICRAF Medium-Term Plan 199 8- 2 000, ICRAF, Nairobi, Kenya Ingram, J., 1990 The role of trees in maintaining and improving soil productivity — a review of the literature, in Agroforestry for Sustainable Production: Economic Implications, R T Prinsley, Ed., Commonwealth... mitigation of land degradation in the humid and sub-humid tropics of Africa, Exp Agric., 32:235–290 Cunningham, A B and Mbenkum, F.T., 1993 Sustainability of harvesting Prunus africana bark in Cameroon: a medicinal plant in international trade, Report of WWF/UNESCO/Kew, People and Plants Programme, WWF, Godalming, Surrey, England Deharveng, L., 1992 Conservation of biodiversity in Indonesian agroforests,... planting of trees by farmers Strictly, biogeographical islands are completely isolated populations, in which island size is positively related to biodiversity The concept has, however, also been applied to shrinking habitats such as woodlands in farmland Although Simberloff (1 988 ) concluded that, in a wildlife conservation context, treating woodlands as islands in this way provided contradictory or inconclusive... Commercialization of Non-Timber Forest Products in Agroforestry Systems, NonWood Forest Products, R R B Leakey, A B Temu, and M Melnyk, Eds., FAO, Rome, 160–175 Michon, G., de Foresta, H., and Aliadi, H., 19 98 Reinventing the forest: damar extraction and cultivation in Sumatra, Indonesia, in People, Plants and Justice, C Zerner, Ed., Rainforest Alliance (In press) Nair, P K., 1 989 Agroforestry defined, in Agroforestry... 1993 Biodiversity and ecosystem function in agricultural systems, in Biodiversity and Ecosystem Function, E.-D Schulze and H A Mooney, Eds., Springer Verlag, Berlin, 15–42 Swift, M J., Vandermeer, J., Ramakrishnan, P S., Anderson, J M., Ong, C K., and Hawkins, B A., 1996 Biodiversity and agroecosystem function, in Functional Roles of Biodiversity: A Global Perspective, H A Mooney, J H Cushman, E Medina,... improvement to the integration of domesticated species in land-use systems (Leakey and Newton, 1994b; Leakey and Jaenicke, 1995) Domestication is an ongoing process in which genetic and cultivation improvements are continuously refined In genetic terms, domestication is accelerated and human-induced evolution Domestication, however, is not only about selection Simons et al (19 98) contend that it integrates... R B., 19 98 Land-use transformation in Africa: three determinants for balancing food security with natural resources utilization, Eur J Agron., (in press) Sanchez, P A., Buresh, R J., and Leakey, R R B., 19 98 Trees, soils and food security, Philos Trans R Soc London, (in press) Schelas, J and Greenberg, R., 1996 Forest Patches in Tropical Landscapes, Island Press, Washington, D.C Schulze, E.-D and Mooney,... to the point that outsiders with capital to invest come in and develop large-scale monocultural plantations for export markets Leakey and Izac (1996) have examined some of the issues requiring consideration to ensure the economic viability of small-scale production and under what conditions small-scale production can be competitive with large-scale production TREE DOMESTICATION IN PROGRESS Since 1993,... McLaughlin, A and Mineau, P., 1995 The impact of agricultural practices on biodiversity, Agric Ecosys Environ., 55:201–212 © 1999 by CRC Press LLC Mellor, J W., Delgado, C L., and Blackie, M J., 1 987 Priorities for accelerating food production growth in Sub-Saharan Africa, in Accelerating Food Production in SubSaharan Africa, J W Mellor, C L Delgado, and M J Blackie, Eds., Johns Hopkins University Press,... capture of intraspecific diversity and the diversification of species on the farm, combines increases in productivity and income generation with environmental rehabilitation and the creation of biodiverse agroecosystems In most places this is just a vision, but there are increasing numbers of examples where the vision is already a reality The body of ecological data from agroforestry research is growing, and . diversifying and intensifying agroecosystems in a way that is beneficial to the environment and can maintain and perhaps enhance biodiversity (Sanchez and Leakey, 19 98; Sanchez et al., 19 98) . In its. Kenya. Ingram, J., 1990. The role of trees in maintaining and improving soil productivity — a review of the literature, in Agroforestry for Sustainable Production: Economic Implications, R. T. Prinsley,. H., 19 98. Reinventing the forest: damar extraction and cultivation in Sumatra, Indonesia, in People, Plants and Justice, C. Zerner, Ed., Rainforest Alliance. (In press). Nair, P. K., 1 989 . Agroforestry