Agroforestry An Integrated Science and Practice

Today, agroforestry is recognized as an integrated applied science that has the potential for addressing many of the land management and environmental problems found in both developing and industrialized nations. The essence of agroforestry can be expressed in four key 'I' words: intentional, intensive, interactive, and integrative. The term 'intentional' implies that systems are intentionally designed and managed as whole unit, and 'intensive' means that the systems are intensively managed for productive and protective benefits. The biological and physical interactions among the system's components (tree, crop, and animal) are implied in the term 'interactive,' and 'integrative' refers to the structural and functional combinations of the components as an integrated management unit. It is often emphasized that all agroforestry systems are characterized by three basic sets of attributes: productivity (production of preferred commodities as well as productivity of the land's resources), sustainability (conservation of the production potential of the resource base), and adoptability (acceptance of the practice by the farming community or other targeted clientele).

Fundamental to realization of the promise of agrofor-estry systems is the multitude of lesser-known woody species that have come to be known as 'multipurpose trees' or 'multipurpose trees and shrubs' (MPTs). The MPTs are the mainstay of most traditional tropical agro-forestry systems. The contributions of MPTs and agroforestry systems in general are usually grouped under two broad categories: production of commodities and ecosystem services. The former refers to enhancement of outputs such as food, animal fodder, fuelwood, timber, and nontimber products, whereas the latter refers to tree-mediated services such as carbon storage, biodiversity conservation, and water-quality enhancement. As a result of major research and development efforts in tropical

Figure 1 (a) Integrating nitrogen-fixing, fast-growing trees and shrubs with crops in the same field simultaneously, or in short rotations of 1-2 years of crops followed by 1-2 years of trees, and using the tree biomass as a nutrient source for crops is an agroforestry technology that has gained acceptance among farmers who cannot afford fertilizers. The photo shows G. sepium grown with maize (Zea mays), a practice followed by thousands of farmers in eastern and southern Africa. Photo credit: ICRAF, Nairobi, Kenya. (b) Winter wheat (Triticum aestivum) intercropped with American ash (Fraxinus americana) in a temperate setting, southern Ontario, Canada. American ash is a hardwood timber species that also has esthetic and ornamental values. The growth habits and crown shape of the tree make it amenable to intercropping, causing only minimal shading to the understory species. As explained, environmental protection is the main motivation for agroforestry in the industrialized nations, where tree integration on agricultural landscape can mitigate some of the problems associated with agricultural production systems such as reduced biodiversity, loss of forest resources and wildlife habitat, and increased environmental hazards including soil erosion and nonpoint source pollution of ground water and rivers. Photo: N. Thevathasan.

Figure 1 (a) Integrating nitrogen-fixing, fast-growing trees and shrubs with crops in the same field simultaneously, or in short rotations of 1-2 years of crops followed by 1-2 years of trees, and using the tree biomass as a nutrient source for crops is an agroforestry technology that has gained acceptance among farmers who cannot afford fertilizers. The photo shows G. sepium grown with maize (Zea mays), a practice followed by thousands of farmers in eastern and southern Africa. Photo credit: ICRAF, Nairobi, Kenya. (b) Winter wheat (Triticum aestivum) intercropped with American ash (Fraxinus americana) in a temperate setting, southern Ontario, Canada. American ash is a hardwood timber species that also has esthetic and ornamental values. The growth habits and crown shape of the tree make it amenable to intercropping, causing only minimal shading to the understory species. As explained, environmental protection is the main motivation for agroforestry in the industrialized nations, where tree integration on agricultural landscape can mitigate some of the problems associated with agricultural production systems such as reduced biodiversity, loss of forest resources and wildlife habitat, and increased environmental hazards including soil erosion and nonpoint source pollution of ground water and rivers. Photo: N. Thevathasan.

Figure 2 Homegardens that consist of intimate, vertically stratified combinations of various food- and fruit-producing trees and crops around homesteads provide food and cash security as well as social and esthetic benefits to millions of farm households around the world, particularly in the tropics. The plants in the photograph, from Jamaica, include: Lower canopy, foreground left: taro (Colocasia esculenta) and greater yam (Dioscorea alata), both edible tuber crops; Lower canopy, foreground right: Guinea grass (Panicum maximum), a fodder grass; Middle canopy, right: banana (Musa spp.) and coffee (Coffea spp.); Upper canopy, consisting of fruit trees: bread fruit (Artocarpus altilis) in background, and mango (Mangifera indica) in front of that. Photo: P. K. R. Nair.

Figure 2 Homegardens that consist of intimate, vertically stratified combinations of various food- and fruit-producing trees and crops around homesteads provide food and cash security as well as social and esthetic benefits to millions of farm households around the world, particularly in the tropics. The plants in the photograph, from Jamaica, include: Lower canopy, foreground left: taro (Colocasia esculenta) and greater yam (Dioscorea alata), both edible tuber crops; Lower canopy, foreground right: Guinea grass (Panicum maximum), a fodder grass; Middle canopy, right: banana (Musa spp.) and coffee (Coffea spp.); Upper canopy, consisting of fruit trees: bread fruit (Artocarpus altilis) in background, and mango (Mangifera indica) in front of that. Photo: P. K. R. Nair.

Figure 3 Shaded perennial-crop systems involve growing shade-tolerant commercial species such as coffee (Coffea spp.) and cacao (Theobroma cacao) under overstory shade trees. The photo shows young cacao plants in between rows of peach palm (Bactris gasipaes) and black pepper (Piper nigrum) in Bahia, Brazil. Photo: P. K. R. Nair.

Figure 3 Shaded perennial-crop systems involve growing shade-tolerant commercial species such as coffee (Coffea spp.) and cacao (Theobroma cacao) under overstory shade trees. The photo shows young cacao plants in between rows of peach palm (Bactris gasipaes) and black pepper (Piper nigrum) in Bahia, Brazil. Photo: P. K. R. Nair.

Figure 4 The dehesa, called 'montado' in Portuguese, is a traditional agrosilvopastoral system practiced extensively in the Mediterranean region of southwestern Europe, where animals (cattle or sheep) graze under scattered trees. The most common tree species are oaks: Quercus ilex ('encina' in Spanish) and Q. suber ('alcornoque' in Spanish). Their acorns are relished by pigs; Q. suber is excellent for cork production as well. Q. ilex dehesas used to be valued more in the past (40-50 years ago) because of the higher animal-feed value of its acorns compared to those of Q. suber; but, today Q. suber dehesas fetch higher value because of the high value of cork. Portugal and Spain are the two major cork-producing countries of the world, and most of this cork is produced in dehesa agroforestry system. Photo credit: David Howlett.

Figure 4 The dehesa, called 'montado' in Portuguese, is a traditional agrosilvopastoral system practiced extensively in the Mediterranean region of southwestern Europe, where animals (cattle or sheep) graze under scattered trees. The most common tree species are oaks: Quercus ilex ('encina' in Spanish) and Q. suber ('alcornoque' in Spanish). Their acorns are relished by pigs; Q. suber is excellent for cork production as well. Q. ilex dehesas used to be valued more in the past (40-50 years ago) because of the higher animal-feed value of its acorns compared to those of Q. suber; but, today Q. suber dehesas fetch higher value because of the high value of cork. Portugal and Spain are the two major cork-producing countries of the world, and most of this cork is produced in dehesa agroforestry system. Photo credit: David Howlett.

agroforestry during the past three decades, a large number of indigenous MPTs have been identified and their multiple role in providing food and nutritional security, medicines, cash income, and a whole host of other products and benefits have been recognized. (Several comprehensive databases of MPTs are available, including the Agroforestree and other databases by ICRAF, various tree data bases by FAO, tropical fruits database, and Forestry Compendium and Forest Products Abstracts database by CABI.) A vast majority of MPTs, however, have not been domesticated let alone exploited commercially. Undoubtedly, a major opportunity as well as challenge in agroforestry lies in domesticating, improving, and exploiting the multitude of these indigenous MPTs.

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