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Trees outside forests and production systems

Photo 34. Multi-purpose riparian buffers in Tanzania (© Bellefontaine/Cirad)

The status, functions and future of off-forest trees raise a complex set of questions in the various production systems where they grow. We have chosen three examples to illustrate this complexity. The first concerns agroforestry in the humid tropics in Africa, a region still not definitively classified as either forest or farmland. The second covers upland coffee-growing areas in tropical Mexico and Central America. These plantations are trying to reconcile economic and ecological imperatives. And the last deals with line-planting systems, where protection and management are one component of a broader system of integrated land use management.

Agroforests: a forest-oriented agricultural strategy?

Throughout the world (and most of history), peasant farmers have wandered, exploited and worked the forests, often refashioning them to suit their own needs. Ecosystems repeatedly subjected to human activity become heavily modified in their composition, structure and functions, sometimes losing a large portion of their tree cover. Some systems, such as the Indonesian agroforests, lean more toward the forest component, but they are nonetheless the outcome of extreme human ecosystem intervention in which farmers tended to singly and collectively appropriate the land and its resources.

Peasant farmer practices

The Indonesian archipelago is still one of the world's last remaining reserves of dense evergreen forest. But a complex reality lies beneath this green canopy. Extremely varied formations of facies, compositions and status are all lumped together as `forest'. Most forms of arboreal vegetation found there have been reconstructed (or simply utilized) by farmers over an area comprising tens of millions of hectares. The originality and importance of the Javanese home garden are a familiar theme in the international scientific literature, where the system is often held up as a model of complex peasant agroforestry that successfully reconstitutes a multistory system of high biodiversity and amazing productivity on a few dozen square meters of land (Soemarwotto, 1987; Christanty, 1990; Karyono, 1990). These gardens form highly characteristics islets of trees within rice paddies, and comprise one of Java's most important off-forest tree reserves.

Less is known about the more extensive agroforestry models established on rather poor soils around the great forest stands in Indonesia's outer islands. These systems, often barely discernible from "natural" forest, nonetheless produce a large portion of the fruit, bamboo, rattan, resin, rubber and spices marketed in the archipelago (Michon, 1999). A prime characteristic of peasant agriculture in the outer islands is the integration of tree resources into agricultural systems which produce not only for the household but also (indeed primarily) for market. This forest/farm integration still functions today, as in the past, as a land clearing system in which so-called "natural" or "primary" forest cover or "secondary" vegetation is initially destroyed. Much of the land originally opened up for rainfed rice cultivation is now given over to perennial crops. This peasant tree-growing effort does include exotics, but also (indeed mainly) local forest species such as cinnamon, nutmeg, clove, rattan, benzoic, dammar resin trees, and many fruit trees such as durian, langsat, rambutan, mango, ellipse butter tree, and latex-producing Ficus. Some of these trees are conventionally monocropped. Coastal forest long ago converted into village coconut groves can be thought of as deforested terrain, and the trees thriving there as "Trees outside forests". But most of these permanent crops grown by peasant farmers are managed in such a complex way as to spark discussion on whether these are "agricultural" or "forestry" systems. Damar, a local, resin-producing, forest dipterocarp, offers a good illustration of peasant tree farming innovations (Box 35).

Peasant agroforestry: forest gardens or plantation gardens?

The dammar example is repeated, with slight variations in the technical processes or prevalent social and institutional models, in the development of other tree crops of forest origin. Batak peasants in the highlands of northern Sumatra established benzoic forest-gardens (Styrax spp) to produce benzoic resin (Watanabe, 1990; Katz, 2000; Garcia et al., 200; Angelsen et al., 2000) Rattan (basically Calamus caesius) is grown in ""monitored fallow" that evolves over time into forest- gardens that can last up to fifty years (Fried, 2000). Other examples share a common shift from extractive techniques - the pivotal product originally collected in situ in the forest - to a production system per se. Spices such as nutmeg and clove, plus benzoic (Katz, 2000) and cinnamon (Aumeeruddy, 1993) are well-known examples. After 1910, Brazilian rubber-tree production quickly replaced the tapping of wild rubber trees, which had been of great economic importance during the last half of the 19th century for people clearing lowland areas in Sumatra and Borneo (Dove, 1994).

This shift generally coincides with a radical change in the status and functions of former forest lands, accompanied by major social upheavals. The resulting plantation-gardens are pivotal and well-established in contemporary agricultural production systems -those with a land-clearing component as the more established systems. All of them look more like "forests" than monospecific, even-aged plantations. Still, we may well ask whether they should then be actually thought of as forest-like, and whether they should be counted under the typical, conventional, forest inventory classifications of "primary forest", or degraded secondary vegetation".

The question of how to define such structures is of interest for several reasons. First, these systems occupy substantial acreage (garden- plantations and garden-forests are far from episodic). They cover tens of millions of hectares throughout the Indonesian archipelago. The small jungle rubber plantations alone account for 2.5-3 million ha in the islands of Sumatra and Kalimantan (Dove, 1993; Youyon et al., 1993). In the provinces of Jambi, Riau and western Kalimantan, they definitely account for most of the area habitually inventoried as "secondary forest" or "exploited forest". The 60 000 ha of dammar gardens are now mapped as "intact primary forest". Almost the entire "forest" belt around the national park in the western part of the province falls into this category. The various fruit gardens ringing the villages of Sumatra, thought to cover 3 million ha, are also mapped as "primary" or "secondary" ". They undoubtedly occupy a comparable portion of land in the provinces of Kalimantan. Their more closely-monitored Javanese counterpart, known as home gardens, probably covers some 3-4 million ha. Benzoic gardens occupy most of the district of northern Sumatra. These figures are comparable to the 4.5 million ha of big oil palm plantations and 3 million ha of industrial forest plantations.

Box 35:

Agroforestry reconstruction: the example of dammar

Peasants in southern Sumatra have a tradition of slash-and-burn cultivation, with rice and coffee or pepper alternating with long periods of tree fallow in a semi-commercial, semi-home production system associated with the gathering of forest products for consumption and sale. This mixed farm/forest economy made only very modest inroads on the "natural" forest up to around the turn of the twentieth century. But as the pressure of a burgeoning population on the land was unmatched by any evolution in cropping practices, forest cover declined. This meant a loss of major peasant resources such as wild latex and dammar resins. At this point in time, peasant farmers came up with the innovation of planting dammar (Shorea javanica) on plots cleared for rice. This did not basically modify the first stages of the former land clearing cycle. The cleared parcel was occupied first by rainfed rice, then coffee, at the feet of which the peasants planted dammar saplings. But some ten years down the road, as coffee production declined, the picture began to change. Following a special technique to ensure the dammar would develop and thrive with a minimum of effort; peasants restored systems that came to be less and less conventional "plantation" and more and more "forest". (Michon et al., 1995; Michon et al., 2000). As the coffee plantations were abandoned, over time the parcel evolved into tree fallow, then secondary forest, gaining further complexity by the later re-establishment of forest species. Farmer intervention in this natural dynamic was minimal. Within the mature plantation, the play of natural dispersal allowed forest species to become re-established. Some 40-50 years later, the dammar plantation strongly resembled, in structure, composition and function, the forest it had replaced: timber forest, dense understorey, extensive biodiversity, and lasting structure. Even though dammar remains the dominant species, up to half the stand can be spontaneous growth. Dammar garden establishment can be interpreted as a true silvicultural process. But should these peasant dammar gardens be compared to "forest"? The point here is to go back to when the plantations began. In the late 19th century, peasant societies began to see rifts develop in the traditional economic and institutional systems which had ensured social reproduction (Michon, 2000). In this context, the innovation of dammar establishment is a clear social expression of a determination to refute a bankrupt forest economy and hierarchical model of agroforestry society. Dammar made individual appropriation of parcels possible within universally recognized borders, on former communal forests, and allowed the planter to establish land tenure for his descendants, a right formerly denied younger brothers. The parcel planted in dammars is a "garden" with all the social and institutional implications of the term.

Peasant forests, a unique forest category

At issue here the fact that the term "forest", customarily used to designate a specific plant fancies, most often describes four distinct and not easily super imposable entities. These are: a biological and ecological system (ecosystem, fount of biodiversity); a collection of economically trappable resources of wood and non-wood resources; a reservoir of collective or individual social value (land-as-legacy, water); and a geopolitical entity (land as territory, already under control or potentially so).

The question is how the agroforestry transformation carried out by Indonesian peasants modifies the components of this multifaceted entity we call "forest". Undoubtedly, is does disturb the structures and some functions of the ecosystem, somewhat reducing biodiversity. But many studies have demonstrated the similarity of the resulting systems to what we call forest. For a biologist, an agroforest is as much "forest" as is undisturbed forest fallow which has grown back. The important thing to note here is that in this case the resemblance to forest is the outcome of technical decisions and not an end in itself. Biodiversity is not a specific production goal for these peasant farmers.

Agroforestry transformation has a strong impact on the natural levels of resource stocks available for adaptation to the economic needs of the moment. Here again, studies have shown that certain typically "forest" resources were actually the product of conservation or restitution, and that most of the pivotal resources of established systems were also conventionally considered by foresters as "non-wood forest products" (even pending prequalification as "agricultural products15 ), but that peasant farmers view these products as "garden" products, a designation which takes account of the physical labour, social stakes and various inputs invested.

Agroforestry transformation often provides an enabling environment for changes in the legal status of land and its resources, i.e., changes in the social context governing these resources. At the local level, agroforestry is viewed as an actual process of appropriation that can transform an area initially collectively owned - the village forest - into private land held by individuals or clans (Peluso, 1993). In the context of interaction between the state and local communities, it puts peasants in a better position vis-à-vis the sovereign State to stake a claim to contested forest lands, at least in terms of customary ownership of land traditionally part of the village territory. With respect to access and control over vital land and resources, agroforestry transformation is always helpful in redefining the basic relationship among the various categories of actors (Dove, 1995; Michon, 2000). In the end, acknowledged appropriation of land by the individual responsible for transforming it makes it possible for future generations to inherit land. This is fundamental in the foundation of families, lineages or clans (Mary, 1987; Michon, 2000).

Most current discussion on the forest centres around the structural, biological or environmental aspects: the economic aspects tend to be viewed primarily in accounting terms. Of course these are the easiest features to grasp, or at least the easiest to enumerate. But definitions, inventories and economic assessments obscure the real discussion. The point is not to precisely chalk up the total forest resources now remaining in the world or to determine their real or potential worth. The issues which these examples of peasant agroforestry raise lie largely outside the need to inventory tree resources at the national or regional levels. They go beyond the confines of an academic debate over the scientific definition of a forest. They get back to the very concept of the various systems of land and tree use as a stake in the web of economic, social and political interaction among the various categories of actors -states, foresters, local communities, or within the community itself.

Coffee plantations: reconciling ecological and economic imperatives?

Arabica (Coffea arabica) is a shade plant climatically well-suited to the tropical mountain areas of Central America and Mexico, where it is mostly grown on small farms (Box 36). In quantitative and qualitative terms, coffee grows best in humid zones where the dry season lasts no more than four months (Alvarez et al., 1992), at altitudes above 1 200 m, in deep and mostly volcanic soils (IICA, 1995; Salinas, 1991). But the crop is often planted in less favourable conditions, on poorer soils, and at lower altitudes, where rainfall is less frequent and the dry season is long and hot (Galloway and Beer, 1997). Under these less than optimal coffee-growing conditions, it is grown in association with shade trees, which maintain a microclimate favourable to coffee growth, and which also allow for diversified production. These complex agroforestry systems can include three storeys of vegetation (Tulet, 1992; Moguel and Toledo, 1999), with coffee combined with banana, fruit trees and forest species.

Despite the recent introduction of new dwarf varieties resistant to yellow rust and tolerant of full sunlight, which has profoundly modified cropping systems (even including the complete removal of shade trees), agroforestry plantations have held strong in many areas, with farmers continuing to grow tree and fruit trees in association with the newly introduced varieties. Not only are such systems economically less risky, they are ecologically more sustainable (Vaast and Snoeck, 1999). What we now have is the coexistence of extremely diverse systems ranging from intensive monocropping to extensive multicropping, including medicinal, fruit, and fodder legume trees, and all stages in between.

Photo 35. Growing coffee under shade. Costa Rica (© Harmand/Cirad)

Various coffee-growing systems

Coffee-growing systems fall into five categories in accordance with complexity, management intensity, and diversity (Fig. 4: table 4):

Traditional coffee-growing systems predominate in El Salvador, with coffee grown in all areas where forest species are present. Multicropping systems are the most common category in Guatemala, Honduras and Nicaragua. The more modern intensive practices are followed by 40 percent of coffee farmers in Costa Rica, some 20 percent in Guatemala, and about 30 percent in Nicaragua and Guatemala. The differences from one country to the next are important, as witness the fact that only 10 percent of Costa Rica's coffee is grown under shade, whereas the figure for El Salvador is 90 percent. As a general rule, traditional systems and multicropping predominate on small farms, whereas the big commercial enterprises tend to farm intensively.

Box 36:

Coffee production and farm size

The countries of Latin America and the Caribbean accounted for over half the world coffee output of 6, 5 million tonnes in 1999. Asia and Africa each produce 1, 2 to 1, 5 million tonnes. The top producer is Brazil, followed by Colombia, Vietnam, Indonesia, Côte d'Ivoire and Mexico with 300 000 t in 1999 (FAOSTAT, 1999, cited in FAO, 2000c). Central America is highly reputed for the quality of its coffee, for which there is great demand on world markets. It provides 15 to 20 percent of total world output. Guatemala, with 200 000 t, is the top Central American producer, leading Honduras (164 000 t), Costa Rica (147 000 t), El Salvador (144 000 t), Nicaragua (65 000 t) and Panama (10 400 t). Coffee is mostly grown on small farms under 10 ha in these countries (Table 5; Rice and Ward, 1996). Small farms under two or three ha account for 40 percent of the coffee plantations in Costa Rica and 71 % in Mexico (Tulet, 1993).

Figure 4 The five major coffee-growing categories in Mexico and Central America (adapted from Moguel and Toledo, 1999).

Many tree species are used for permanent shade. From Mexico (Soto-Pinto, 2000) to Nicaragua (Galloway and Beer, 1997), Inga spp. are the most popular choice. These fast-growing, nitrogen-fixing legumes exhibit a great capacity for post-trimming regeneration. They retain their leaves during the dry season, and produce fuelwood and service wood. In low-lying areas of Honduras and Nicaragua, Gliricidia sepium is a common choice, though it does have the disadvantage of losing its leaves during the dry, hot season. The legume Erythrina poeppigiana is the most common shade species in Costa Rica. It is valued for its capacity to withstand frequent and drastic pruning. The practice of planting windbreaks in coffee plantations has developed in a number of countries. The many species planted include Cupressus, Eucalyptus, Croton, and Cordia (Galloway and Beer, 1997).

Table 4. Farming systems and coffee farm size in Mexico and Central America



Total area
Under coffee
(x 1 000 ha)

Coffee in
crops (%)

Total farms

Small farms















275 000


Costa Rica






55 000


El Salvador






35 000








34 000








38 000








15 000








31 000


Source: Rice and Ward (1996) and FAO Statistics (2000).
* in % of total area under coffee
trad. : traditional
interm : intermediate (traditional and commercial multicropping)
techn : technified (specialized system under shade and unshaded monocropping)

Figure 4 The five major coffee-growing categories in Mexico and Central America (adapted from Moguel and Toledo, 1999).

The multiple benefits of agroforestry coffee-growing

Agroforestry coffee-growing systems offer numerous advantages from the ecological standpoint. In countries such as El Salvador, the coffee-growing zone constitutes the main area of manmade forest. The rugged landscape profile created by the tree strata increases ecosystem resistance to exceptional weather events such as hurricanes. The role of tree cover in soil conservation is primordial, especially on slopes. Trimming residue inputs (Box 37) check rainfall runoff and constantly enrich organic matter in the soil. The nutritional requirements of shaded coffee are fewer than those of coffee grown in full sunlight, and at the same time the retention and recycling of mineral elements are greater. Both factors imply fewer fertilizer inputs and less soil loss from leaching and rainfall runoff.

Microclimate regulation and organic enrichment of soil also favour wildlife biodiversity. In Costa Rica, a highly diverse population of arthropods has been reported under shaded coffee (Perfecto et al., 1997. Cocoa and coffee plantations traditionally harbor at least 180 species of birds, many more than other kinds of farmland (Rice and Ward, 1996). Tree strata offer essential fauna habitat and indeed the agroforestry coffee systems are part of the biocorridors essential to the preservation of wildlife biodiversity. Mixed plantations of cocoa or coffee with banana and citrus, are, together with shaded coffee plantations, thought to contain some 75 percent of the specific wealth of a forest habitat.

These coffee-based agroforestry systems also function as carbon sinks for the reduction of greenhouse gases. Alvarado et al. (1999) estimate that Guatemalan coffee agroforestry systems store an average 30 t/ha of carbon in the biomass and leaf litter.

Diversified productivity in agroforestry coffee systems

Agroforestry coffee-growing systems are also economically advantageous because the trees ensure a more balanced income for coffee-growers. Diversified coffee farms are in a better position to withstand price slumps in the coffee sector (Bart, 1992). These growers tend to manage their holdings much less intensively, purchase fewer inputs, hire fewer labourers, and give more attention to their fruit and foodcrops.

Shaded plantations also have a great fuelwood potential, supplying 8.5 m3/ha/yr from 635 trees/ha of Mimosa scabrella; 1 250 trees/ha of Inga densiflora and 330 trees/ha of Gliricidia sepium (Beer et al. (1998). Household fuelwood needs alone would justify the presence of these tree species in coffee plantations. Some shade trees such as Cordia alliodora and Cedrela odorata also supply timber. Beer et al. (1998) report that the average commercial timber output of Cordia alliodora ranges from 4 to 15 m3/ha/yr. A stand of 100 Cedrela odorata grown in association with coffee on one hectare of land in Turrialba, Costa Rica, produced a commercial volume of 4 m3/ha/yr (Ford, 1979), generating an annual profit equivalent to 10-15 percent of the coffee harvest. Once the trees become harvestable at the age of 15 or 20 years, they generate an income two to three times as great as the annual coffee harvest.

Trees on coffee farms can normally be cut for household use of the wood, but a permit is required for transport and sale. This permit is not easy to obtain, a disincentive to coffee-growers who might otherwise plant timber species on their farms. Legislative progress has been made in some countries, however. In Costa Rica, the new 1996 Forest Law authorizes the logging and sale of wood and tree products from forest plantations, which includes the agroforestry systems. This legislation, combined with subsidies for reforestation, induced many farmers to replace traditional shade tree legumes by commercially valuable timber species, with an eye to diversifying their sources of income or accumulating savings (Tavares et al., 1999).

Agroforestry coffee systems in Mexico and Central America are ecologically and productively important. They are better-suited to environmental constraints than monocropping, ensuring economic viability and sustainability for family farms through product diversification.

Linear tree systems: strategic components of integrated land management

Both rural and urban areas are given organization and structure by linear tree systems. They delineate property boundaries, protect against the elements and against livestock incursions, preserve the privacy of people's gardens, beautify the landscape and provide isolation and shade. In town and country alike, trees are as essential to the external landscape as to the inner well-being of those who dwell among them.

Box 37:

Shade trees and coffee production

Trees create a microclimate favourable to coffee growth and production. Their shade attenuates temperature variations and keeps the foliage and upper soil layers from overheating, making them less vulnerable to water stress during the dry season. Shading exercises a kind of control over coffee production, reducing swings from high to low yields, and prevents premature branch mortality from full sunlight or the burden of too many coffee berries. Shade plays an important role in coffee plantation sustainability Fodder legume trees, trimmed several times a year, improve coffee plant nutrition by fixing nitrogen and recycling nutrients, the trimmings being left on the ground. According to Vaast and Snoeck (1999), the amount of dry matter produced in the form of tree wastes or litter by Inga spp. or Erythrina spp. ranges from 2 to 14 t/ha/yr, returning some 60 350 kg/ha/yr of nitrogen to the soil. Symbiotic N fixation by these tree legumes is estimated at 30 to 60 kg/ha/yr. Recent studies in Guatemala and Costa Rica, (Guyot et al., 1996 ; Muschler, 1998) showed that shade trees lengthened the growing period and ensured better coffee quality in terms of biochemical composition (caffeine, fat content, chlorogenic acid), and physical properties (berry size and density), as well as the organoleptic properties (taste and fragrance) of the final brew.

Their future in towns is pretty much guaranteed by the evolving attitudes of urban-dwellers, but the story is quite different in rural areas. Linear tree formations and their resources rarely appear in the national forest inventory statistics, and the swiftly changing agricultural and environmental circumstances threaten to hasten their demise. If they are not to disappear, we need to learn to think of them as a full component of integrated land management.

Different types of linear systems

Linear tree systems can be divided into four broad categories, in accordance with structural arrangement, function and origin.

Hedgerows are a linear composition of trees and/or shrubs, free-growing or trimmed, of variable height, whose function is to fence off or shelter (IDF; 1995). Two centuries ago in Europe, hedges forming a bocage landscape (Schmutz et al., 1996), made up of irregular-sized fields, criss-crossed by hedges, ditches and wooded slopes, here and there dotted by single trees, and accompanied the fragmentation of the vast plains. This is now a vanishing landscape in France, and the hedges have been levelled (INRA, 1976). In the Fouta Djalon region of Mid-Guinea, food crops are always fenced in by hedges. In northern Cameroon and in Chad, the inhabitants used to plant thick hedges as fortifications to repel invaders (Seignobos, 1980). The Bamiléké area of Cameroon is famous for its living fences lining fields and paths, and deadwood hedges built around homes. In the Sahel, Euphorbia hedges are widely used to control wind erosion. A hedge made up of tall trees dense enough to ensure optimal porosity, such as the composite hedge (Tourret, 1997), can be compared to a wind-break. The establishment of residential zones in urban areas has tended to favour hedge-planting, mostly by private homeowners.

A windbreak is a narrow row of trees planted in fields bordering a farm plot (IDF, 1981). A shelter-belt is a wooded strip, often natural, and somewhat wider than a windbreak, found in more extensive cropping zones. A windbreak of optimum porosity (some 25 percent), would consist of a single row of even-height trees with touching canopies and an understorey of bushy species that do not lose their leaves even in bouts of high winds (Cornelis et al., 2000). Windbreak spacing should be roughly 15 times the average height of the mature trees for greatest effectiveness (FAO, 1986). Windbreaks are basically found in landscapes largely fashioned by human hands, where farming is intensive (Box 38). They are frequently associated with hydroagricultural development along the major rivers in arid zones. Abundant around fruit-tree orchards, they are becoming increasingly common around market-garden plots in the vicinity of the big cities (Louppe, 1991); Lamers et al., 1984). They are still rare in rainfed farming, but are beginning to be seen in heavily populated areas, primarily to mark land boundaries (a role also played by living fences). They are not very common in extensive agriculture, except in certain livestock production areas.

Line-plantings along roads, canals and railway lines appeared in mid-nineteenth century Europe in response to an active policy of urbanization and land use planning. These rows of roadside trees, now an ageing resource, tend not to be renewed for reasons of road safety. Recent road developments envision the widening of country roads without levelling the more striking hedgerows (Softner, 1995). Quite the reverse is true in urban areas, where linear tree-plantings play an important role. No urban building project can afford to scrimp on greenery.

Riparian buffers, consisting of a narrow and sometimes discontinuous fringe of trees, are a formation born out of occasional flooding in alluvial forests, gallery forests or cleared, drained and cropped former mangrove areas. Growing close to water they are subject to regular flooding. Floral composition and size depend on surface and groundwater flows and overflows. Many species of trees, with powerful root systems and adapted to this specific environment, help check riverbank erosion in riparian buffer systems. Farmers, fisherfolk and hunters often have conflicting views on these streambank formations.

Functions in linear systems

Off-forest linear tree systems confer the dual ecological and aesthetic benefits of checking wind and water erosion, regulating floods, purifying water, reducing air pollution, and enhancing the scenic aspects of our surroundings. In socioeconomic terms, they provide a network of urban greenery, marking land boundaries, producing wood or forage, and creating rural and urban employment.

Lines of trees and shrubs planted perpendicular to the steepest slopes help to check runoff and water erosion in fields (Perez et al., 1997). They favour rainwater infiltration by improving soil porosity, thus acting to some extent as flood regulators. Streambank strips or fringes of trees help hold back floods, breaking the current and dissipating the energy of raging floodwaters meter by meter, attenuating their divesting effects (Ruffinoni, 1997). Deep-rooted, well-anchored16 native species as opposed to exotics (which can easily topple, fall in the river and, carried on the crest of the flood, cause dangerous pile-ups when they hit the bridges) are much better deterrents of flooding. Streamside buffers are most effective on banks with gentle, regular slopes (Lachat et al., 1994).

Photo 36. Bocage landscape in the Belgian Ardennes near Francorchamps (© Bellefontaine/Cirad)

By acting as buffers between the aquatic environment and cultivated fields, streamside trees help to reduce water pollution, which is also of financial interest in the short term (Box 39). Land prices in southern Sweden, for example, range from 18 000 to 30 000 francs/ha, and the cost of purifying nutrient-polluted water is estimated at 150 francs/kg of nutrient (combined phosphates and nitrates). This amounts to 8 200-13 000 francs/ha/yr (Petersen et al., 1992) The establishment of a riparian tree buffer 10 m wide would become profitable in only three years, given the self-purifying capacities of these plant systems

Row plantings also serve to protect wildlife. Trees fringing rivers and streams are a source of great biological richness, providing spawning-grounds for fish and shellfish, even as their shade acts to limit the development of aquatic flora, thus reducing problems of eutrophication. Rows of trees also host myriad underground lifeforms: In Côte d'Ivoire, for example, the population of worms and termites underneath a single line of six-year-old Acacia mangium is markedly higher than under Pueraria grass fallow, and much higher than under the groundnut crop (Quattara, cited in Louppe et al., 1996). Bocage landscapes also comprise a habitat essential to the survival of many insect, rodent and bird species. Continuous, uninterrupted threads of hedgerows, windbreaks and riparian buffers, especially those with several rows of trees, provide biological corridors through which terrestrial wildlife can move from woods and forests to watering-points. Woody species, often sprouting from seeds distributed by animals, tend to re-establish themselves at the foot of linear tree systems, increasing ecosystem biodiversity.

Box 38:

Windbreaks and higher yields

Spectacular yield increases of 80 to 200 percent have been achieved in arid and semi-arid African regions with on-farm windbreaks. In Tunisia, potato yields doubled and tomato yields rose by 1.7 percent. Trifolium yields in Egypt more than doubled (FAO, 1986). In the Valence region of France, a windbreak 20 m high planted broadside to the mistral assures an average gain of 10 quintals/ha on 200 m of irrigated maize plot (Schmutz, 1997). Increased insect pollination, more effective tie-up and better fruit quality from reduced bruising are some advantages of protecting fruit-trees with windbreaks. . In the Maggia Valley of Niger, two four-year-old neem (Azadirachta indica) windbreaks boosted millet yields by 29 percent (11 to 56 percent by distance from the windbreak) and 23 percent, less the lost space under the trees. Plant growth was improved with a height gain of 0,5 to 0,7 m (Madougou et al., 1987).

Rows of trees are often planted to protect infrastructure from wind, rain, cold or sun. This solution is common in livestock production systems, where trees are planted around buildings to regulate building temperatures, and around meadows to break the wind, increasing livestock energy exchanges, with an indirect impact on available food resources (FAO, 1986).

Box 39:

Riparian buffers as water purification systems

Provided they are planted on slopes, even very gentle slopes, riparian buffers, hedgerows and windbreaks purify water by taking up a significant amount of phosphates, nitrates and pesticides. A young riparian buffer can take up an average 0.38 g/N/day/m2. This is 38 times as much as a grassy meadow (Ruffinoni, cited in Balent, 1996). The restoration of a riparian buffer some 50 m wide along a 120 km stretch of the Garonne in France would, during the plant cycle, remove some 5.6 tonnes/day of nitrogen that otherwise ends up in the river

Some line plantings also have a productive function. Hedgerows, planted to channel livestock and keep them from roaming, also provide fodder. Closely planted Gliricidia sepium forms a living fence in Indonesia, where its clippings are used as fodder. In Vanuatu, living fences of bourao (Hibiscus tiliaceus) are trimmed yearly and the leaves fed to cattle. When livestock producers can afford to do so, fodder trees lining fields are also used as fodder banks during hard times in accordance with a fairly intensive green fodder livestock feeding system very common in southeast Asia and some parts of East Africa (Kleinn and Morales, 2000). Linear tree systems also contribute fuelwood, timber and chipwood (Box 40).

Box 40:

Wood and crop productivity in connection with tree rows

Fuelwood from hedgerows is mainly for home consumption (Pointereau, cited in Balent, 1996). In Normandy, France, yields of some 3 t/km/yr of woody dry matter are quite common. Similar figures are reported in Loire-Atlantique, with 25 to 30 steres/yr, i.,e., an average annual increase of 0,5 to 0,7 steres/100 m for a 15-year rotation (Jégat, 1994). One km of hedgerow produces an average 1,5 TOE/yr/ of fuelwood, the equivalent of some 8 steres of wood and 6 m3 of chipwood, or again 70 and 30 percent of the energy produced. This is a fairly substantial source of energy (Pointereau and Bazile, 1995). The highest net primary productivity in Europe (Stroffek et al., 1999) is in mature forest on the Rhine alluvial plains in Germany. In the dry tropics, irrigation schemes hold out new promise for development, using trees to enhance drainage or percolation waters, and windbreaks, clumps of trees and shelterbelts have been established in areas too difficult to develop for agriculture. In the irrigation schemes of the Senegal River Valley, Eucalyptus camaldulensis yields range from 12 to 22 m3/km/yr at the age of 3,5 years, attaining 11,5 m3/km/yr at the age of 6 years despite a 50 percent mortality rate (Harmand, 1988). In the sub-tropics, dual tree rows, planted to protect irrigated cotton, produce 30 m3/km/yr for the first row of Eucalyptus harvested at age 15, and 15 m3/km/yr for the parallel row of Casuarina harvested at age 20 (FAO, 1986). In the Maggia Valley in Niger, without irrigation but with a shallow groundwater level, the progressive pollarding of a windbreak at 2.5 m from the ground every four years provides income for villagers. One km of neem (some 225 harvestable trees), can supply 110 m3 of wood to meet the needs of 220 people for one year (Madougou et al., 1987).

The future of linear tree systems: toward long-term integrated management

Urban citizens' associations have imposed certain controls to ensure tree survival, but the management of non-forest trees in rural areas is usually strictly up to the local farmer or livestock producer. Access rights are bound up with property rights, even though, admittedly, administrative permits are required in some countries for the harvest and sale of valuable tree species. If we are to ensure the survival of linear tree systems, we will have to come up with ideas for their long-term management that involve all actors in an integrated land use planning effort.

Photo 37. Riparian buffer tree system in the Alagnon Valley of Auvergne, France. (© Bellefontaine Cirad)

Box 41:

Tree grants in France

Land consolidation, which is often imposed upon farmers, usually spells the disappearance of the hedges and trees punctuating a bocage landscape. In order to maintain this tree capital, the French Institute for Forestry Development (IFD, 1995), set up tree grants paralleling the exchange of parcels. The principle is to guarantee that owners will get back an equivalent land and tree capital after the exchange, with full ownership, usufruct, or ownership without usufruct. There is, in fact, a great temptation for owners to fell standing timber prior to consolidation. These incentive procedures assume ownership adherence to and respect of the rules. Each single tree or row of tress is accounted for and assigned a value. The species and volume of exploitable logs are assessed for specific timber species. For fuelwood, the reference value is one stere of easily accessible standing oak (IDF, 1995 ; Pivot et al., 1995). Some owners receive a wood value exceeding the one they abandoned, and this case there are equivalency procedures. In the reverse case, they receive a premium in cash (or in kind in the form of fuelwood).

Of the 2 million kilometers17 of hedgerow believed to be present in France at the height of the bocage era, nearly 65 percent (1.3 million km) were destroyed during the twentieth century process of land consolidation. In England and Scotland, 25 percent of linear plantings were lost from 1946 to 1974. In Ireland, the figure was 14 percent between 1937 and 1982 (Pointereau and Bazile, 1995). Regression can be swift and insidious. Some countries have set up monitoring and protection systems to remedy the situation, mindful of the expectations of the various actors concerned (Box 41). But the choice of a management model depends primarily on the social context, especially where the issue is management of a public asset for which farmers may not feel responsible (Jégat, 1994), even though hedgerows benefit the entire community (Touret, 1999).

Photo 38. Olive grove protected by a cypress windbreak in Volubilis, Morocco. (© Bellefontaine/Cirad)

Box 42:

Windbreaks in the Maggia Valley in Niger

Deforestation of the Maggia Valley watershed in Niger began around the year 1930, after which the denuded slopes were dessicated every dry season by violent and persistant winds. To protect the watershed environment and the valley land, the first windbreaks were planted in 1975, mostly dual rows of Neem (Azadirachta indica) intended to become a public asset growing on private fields. By 1987, over 420 km of windbreaks had been planted, with a success rate of over 72 percent after three years (Madougou et al., 1987). This fast-growing tree crop soon came to be seen by farmers as a nuisance. The subsequent and numerous questions that then arose asked who benefited from such by-products as posts, service wood, fuelwood, fodder, and the neem's insecticidal fruits. People also wondered to whom the trees belonged and how they could be exploited to ensure their survival despite the freely grazing livestock roaming the site during the dry season.

Initially, the farmers had allowed the Forest Service to set up a special jurisdiction. Valley-dwellers were convinced that the trees and their products were the property of the Forest Service, and that the only benefit to them as farmers was crop protection from the winds and better yields as a result. The neem, which had been planted as a joint operation by the landowners and by salaried workers, were considered by some to be private property during the crop season, but freely accessible community property the rest of the year. Many, however, now believe that the windbreaks are destined to disappear unless effective, year-round protection is guaranteed for neem and its products. One solution would be to self-finance a watchdog system through the sale of neem products, with the transhumant pastoralists made part and parcel of the neem protection effort.

Land managers concerned about the future of linear tree systems have their institutional work cut out for them. Inventories must be made of the various mechanisms, recent local experiences, and traditional usages, highlighting their practical scope, and their good and bad points. Some countries will require draft legislation, or changes in existing laws and regulations, to give official sanction to the most appropriate solutions, and to try out new ideas. The establishment of a genuine environmental management policy for rural and urban landscapes has become a twenty-first century imperative. Recognition of the land tenure status of linear tree systems growing on non-forest land, training of the economic actors managing an asset common to all inhabitants in a given locale, fiscal and financial incentives, well-chosen subsidies within an overall action context that includes support for the marketing of wood and other products - these are all steps that can be taken to avoid the sidelining of linear tree systems (Box 42).

15 Within Indonesian statistics, damar, rattan and cinnamon are still listed among the principal agroforestry products as "non-wood forest products", whereas nutmeg, clove and benzoin are listed as products of agricultural origin. Hevea's status is in discussion (it is currently considered a plantation product) but it may be reclassified as a forest product. This reclassification would mean the administrative transfer of millions of hectates of peasant plantations to the Ministry of Forests.

16 Flood pressure exposes the upper roots of riverside trees through water erosion, but such trees remain firmly anchored to the bank.

17 Conventionally, one km of hedgerow with a ground width of 10 m is considered the equivalent of one ha of forest (INRA, 1996). For Schmutz et al. (1996), the area of linear plantings is obtained by multiplying their length by 5 m for bushy hedgrows and by 10 m for rows of tall trees.

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