Overstory #232 - Trees outside forests: Functions and significance
Trees outside forests, a fundamentally multipurpose resource, are more intimately linked to the society around them than forest trees. Their productive, ecological and cultural functions are incisive, and their social, economic and environmental roles help to sustain households and household income. They are instrumental in national and international economies. They promote the conservation and sustainability of tree resources. A review of their role in peasant income acquisition strategies and potential value as economic and market indicators constitutes a challenge and innovation in the approach to forestry.
A multi-purpose, multi-use resource
All trees can be described as potentially multi-purpose, but the potential uses of Trees outside forests are more clearly evident. The wealth and diversity of their uses and services create a permanent, daily interaction with people that can be seen in production and research strategies, as in Income mobilization.
Trees outside forests, which may be spontaneous or planted, are usually cultivated and tended by people. They may be exotics, or perhaps species domesticated and bred by local populations.
Shade and shelter, environmental protection, and enhancement of rural and scenic surroundings are the main reasons cited by industrialized country farmers for leaving trees standing in their fields (Auclair et al., 2000). In the developing countries, however, farmers are particularly apt to favour, select and plant species which can offer a range of goods and services. This is the best way of managing land, labour and capital (Arnold, 1996). The babaçu palm tree in northern Brazil has long been part and parcel of the shifting cultivation system (May et al., cited in Arnold, 1996). In Vanuatu, trees are highly protected as biological diversity shrinks (Walter, 1996). Where species are few or rare, people tend to tap a wide range of potential products, whereas potential uses tend to remain dormant in a more diversified environment (ibid).
Trees outside forests represent a major food source for rural populations. Parklands of néré (Parkia biglobosa) and shea-nut (Vitellaria paradoxa) are maintained because of the food items they offer (such as pods and nuts used as condiments or butter). People in West Africa consume an estimated annual ten kg of shea-butter per person (Boffa, 2000b). Date palms are valued for their fruit in Iraq, not to mention shade and crop protection. In sub-Saharan Africa and in the Sahel, the pericarp of the fruits of the doum palm (Hyphaene thebaica) and of Boscia senegalensis are crushed to provide a meal that can stand in for cereal grains when food is short (Bernus, 1980). Trees outside forests have also been called "trees that nourish" (Bergeret and Ribot, 1990), a term which is really meaningful for landless people who make beneficial use of the tree products to which they have access. Women, the first to be concerned by this harvest, possess the skills to store and process these leaves and fruits so that they will be on hand to feed the family all year round. A study done in Java showed that 60 percent of the family's food comes from home gardens in which trees are prominent, and that these gardens are mostly managed by women (FAO, 1989).
Trees outside forests not only provide products that enhance food security, they also help to promote dietary balance, diversity and good health. Tamarind (Tamarindus indica) fruits are especially rich in Vitamin C. Baobab (Adansonia digitata) leaves, eaten fresh or dried, are a good source of Vitamins A, B, and C, calcium, phosphorous, and iron (Boffa, 2000a). Scoones et al. (1992) underline the importance of edible products from forests or complex agroforestry systems, (the contribution from Trees outside forests is even higher in this respect). All these products may provide simple snacks during work or travel (Ogle and Grivetti, 1985), or, like baobab, they may be eaten when food is short, or, again serve as a basic food, like breadfruit (Artocarpus altilis) or Tahiti chestnut (Inocarpus fagifer) (Walter, 1996). Some Trees outside forests have medicinal uses, with parts such as leaves, roots and bark providing the raw materials for medicinal and veterinary products.
The fodder and browse of Trees outside forests are a major source of livestock feed. While such products are fairly untapped in humid zones except in the urban and peri-urban areas of developing countries, they can mean the difference between life and death in arid and semi-arid zones. Livestock owe their continuing good health or survival to tree fruits or leaves to round out or balance the daily fodder ration in many regions of the world. Trees are the only source of green forage during the lean times before the rains. Fodder trees may also be planted or left standing near home where stockraisers no longer have access to specific rangelands, or where there are not enough people to drive the animals.
Trees outside forests provide many other services for livestock. They offer comfort and shelter for animals, such as Pinus radiata windbreaks in New Zealand, Samanea saman and Albizia shade-trees in the sub humid tropics, and the twin rows of beech (Fagus sylvatica) which grow on the Norman slopes in France. Bushy, thorny hedgerows are planted to mark boundaries and channel herd access and movements. Toxic euphorbs (Euphorbia tirucalli, E. balsamifera), and Gliricidia sepium are planted very closely in Indonesia to form living fences, and their clippings used as fodder. The leaves of Hibiscus tiliaceus feed cattle in Vanuatu, and Hawthorne (Crataegus oxyacantha) is trimmed to form thick, impenetrable hedgerows in Europe.
Trees outside forests also play a key environmental role. They mark off territorial boundaries, a first stage in land appropriation, demarcate holdings, decorate living quarters and provide welcome shade for man and beast in the hot countries. Shade trees are beneficial components of coffee, cocoa and tea plantations in some agroforestry systems. Cordia alliodora and Erythrina poeppigiana shade coffee plantations from the sun's glare in Latin America. Looming on the horizon in arid countries, trees are used by nomadic peoples in arid countries as markers. Most place names in Touareg regions make reference to trees (Bernus, 1980).
Trees outside forests are imbued with symbolic, cultural, and even religious value. They crop up in so many aspects of culture: language, history, art, religion, medicine, politics, and more. Folklore, stories and proverbs also attest to the symbolic significance of trees in human thought (Calame-Griaule, 1980 and Kaboré, 1987, cited in Boffa, 2000b). They are sometimes called "trees of wonder", when due to their venerable age, isolated trees have reached impressive size and girth and passed into local legend. Watkins (1998) has shown how such trees are valued in the U.K. for their beauty, solemnity and mystery.
One could go on with the long list of goods and services trees provide, such as fuelwood, raw materials for crafts, tool handles and furniture-making, or wood for housing and shelter. Over a million people live in houses either made of bamboo, or which use bamboo as a structural element, wall-panels, or roofing (Kumar and Sastry, 1999). Also worth mentioning are such products as resin, latex or gum Arabic, or again the extraction of essential oils and the production of cosmetic products. The same tree often has several uses - rarely is a species maintained for a single use or product. All parts of the tree are harnessed to make products for a wide range of uses.
A key environmental resource
An African adage has it that "Earth is not a legacy we inherit from our parents, but rather a loan from our children". It took two million years to arrive at the one billion men and women alive on the planet by the year 1800. By the year 2025, world population is projected to approach nine billion, of whom over seven billion in the developing countries. One billion people live in poverty (World Bank, 1995), and more than 800 million never get enough to eat (FAO, 1996a). The challenge is clearly to ensure that natural resource conservation and sustainability efforts are sufficient to reduce poverty and ensure the present and future inhabitants of town and countryside sufficient livelihood to guarantee food security. Trees outside forests can play a leading role in meeting resource conservation and management needs in both rural and urban areas Urban forestry is already crucial to environmental quality, and will increasingly be so in future, procuring the unequivocal ecological benefits of bettering the climate, limiting and channelling urban population growth, recycling waste waters, abating noise, and attenuating atmospheric and noise pollution (Greye and Deneke, 1978, cited in El-Lakany et al., 1999.
For soil and water
The rate of soil degradation has now largely outstripped soil regeneration. This situation cries out for agricultural systems that respect the environment, nurture biological diversity, and maintain soil fertility. Trees outside forests are well-placed to meet this challenge effectively. In dense or thin stands, line plantings, singly or in hedgerows, trees preserve the organic matter contained in the soil (Roose, 1994) and boost its fertility. This is universally acknowledged, as is the role of trees in halting the advance of the desert, checking wind and water erosion, facilitating the percolation of rainwater, and enhancing agricultural production in the long term.
In much of the world, pioneer encroachment upon the forest is a factor in natural resource degradation, so it is essential to conserve sufficient tree systems in all their various forms and layouts. Line-plantings are a source of great biological richness for ecological preservation, bio conservation, water purification, and storm protection. Trees growing outside forests in line-plantings, clumps or woodlots have a special role in conservation-oriented water, biomass and soil fertility management. Where properly established, tree plantings tend to replace more mechanical approaches to soil and water protection, conservation and restoration.
Trees outside forests, regenerating spontaneously and/or planted to maintain or extend tree cover, are of great benefit in watershed management, reducing soil degradation and controlling desertification. The rivers and streams of mountainous zones and their ecosystems are protected by streamside trees and those growing on farmland. The 1992 UNCED stressed that mountains are a major reservoir of water, energy and biological diversity, and that mountain environments are essential to the survival of world ecosystems.
For biological diversity
No country can afford to ignore its phytogenetic resource base and at the same time expect to sustainably increase food supplies and address the issue of the environment, including climate change. Generations of farmers have given local communities an important role in the conservation and enhancement of these now seriously endangered resources (Leipzig Declaration, 1996). In the Sahel, the greatest threat to the maintenance and sustainable development of genetic resources is posed by the overexploitation of wood resources. The risk that tree species or populations may vanish is aggravated by recurrent bouts of drought. Species vary in their ability to withstand these attacks. Chad reports substantial losses of its stands of Acacia senegal, Anogeissus leiocarpus and Dalbergia melanoxylon. An estimated 100 000 ha of savannah are lost every year in Cameroon and Senegal. Species such as Acacia nilotica, Pterocarpus lucens, Sclerocarya birrea, Prosopis africana, Lannea microcarpa and Dalbergia melanoxylon are extremely sensitive to the impact of climate (FAO, 2001c).
There are two strategies for protecting these assets (Secretariat of the Convention on Biological Diversity, 2000). One is ex situ conservation in botanical gardens, arboretums, and conservation stands. In this context, genetic improvement and breeding programmes in the Sahel are already holding out serious promise for the future of Anacardium occidental and Faidherbia albida (Leipzig Declaration, 1996). The other strategy is in situ conservation, where farmers draw upon their knowledge of the interactions between the environment, genetic resources and their own management practices to protect biological diversity. Home gardens in many countries offer refuges for certain rare plant and tree species contributing to the biological spectrum. This is also true of agroforests, with their high densities and great range of woody and non-woody species, which render environmental services comparable to those of the forest.
Concerning the biodiversity of wildlife, areas of open tree cover support a more substantial and diversified biomass than forests. Serengeti in Tanzania is the best-known example of this: the park has the most impressively large herds of antelope in the world. Tree savannah furnishes shade, protection, browse and branches where animals can shelter, rest, or make their homes.
Hedgerows, windbreaks and woodlots on farmland also constitute refuges for wild plants and animals, forming islands of biodiversity and biological corridors. This function is very familiar to both hunters and farmers, who favour the conservation of hedgerows and woodlots. Farmers may harbour reservations about the resultant increase in bird and rodent pest attacks on their crops, but they also welcome the presence of pollinating insects like bees, insect-eating birds and animals useful for biological pest control. Often woody species (some rare or uncommon), grow and thrive at the foot of tree rows, their seeds having been distributed there by animals, in a further contribution to biodiversity. The existence of many animal species has been safeguarded by the planting, maintenance or restoration of bocage hedges. Trees lining rivers and streams are a source of great biological richness, providing spawning-beds for fish and shellfish, even as their shade acts to limit the development of aquatic flora, thus reducing eutrophication. These riparian woods also function as biological corridors for terrestrial wildlife. In the management of non-forest trees on farmland, the final goal is sustainable biodiversity in which a balance is struck between the beneficial impacts and the control (if not the elimination), of harmful ones.
Trees act as both reservoirs and potential sources of carbon. The role of tropical forest ecosystems in carbon storage and release is beginning to be known in the global context of the biosphere, in the regulation of atmospheric carbon, and in the reduction of greenhouse gases. The quantification of carbon sources and sinks and of wastes due to human activities is currently a major concern of the scientific community (Alexandre et al., 1999). Changes in land use, especially slash-and-burn practices and the resultant deforestation of tropical forest, are now responsible for some 20 percent of CO2 emissions (FAO, 2001a). According to the Intergovernmental Panel on Climate Change (IPCC), carbon fixation from reduced deforestation, forest regeneration, and intensified planting and agroforestry practices would amount to the equivalent of 12-15 percent of CO2 emissions from fossil fuels from 1995-2050 (FAO, 2001a).
It became clear during the international negotiations on global climate change leading up to the Kyoto Protocol that carbon could become a new "product" needing to be monitored, quantified and managed in new ways, compared to past treatment of the issue, and that the element will provide a new rationale for activities affecting climate change. Decisive changes must be made in the energy, transport and industrial sectors, as in agriculture and forestry. The impact of Trees outside forests on reducing deforestation, stabilizing soils and ecosystems and sequestering carbon will become increasingly meaningful.
Selected forest management practices can slow the accumulation of atmospheric carbon. One item on the agenda of the 1997 Eleventh World Forestry Congress in Antalya, Turkey, was the expansion of carbon sinks by "the establishment of plantations on non-forested land, (...), the increase of forest cover on farmland or pasture through agroforestry systems" (Brown, 1997). Unruh et al (1993) estimated the amount of stored carbon in aboveground and underground biomass in 21 different agroforestry systems in subsahelian regions, concluding that the environmental role of agroforestry in terms of retaining organic matter in the soil and reducing deforestation (and thereby reducing CO2 emissions) is more important than its straightforward effect of carbon sequestration. Planting trees in non-forest areas as part of integrated land management efforts could help maintain stored carbon at acceptable levels. Much of the thinking on how Trees outside forests relate to climate regulation is still at the research stage. Resources should accordingly be mobilized to assess the importance of Trees outside forests within the carbon cycle (Alexandre et al., 1999) -- they have already proven rather effective in improving microclimates.
Consideration of the beneficial impact of Trees outside forests, particularly in terms of development issues such as enhanced food security, poverty reduction and ecosystem conservation has highlighted the critical need for hard and fast facts and figures to reliably underpin promotion and support policies for Trees outside forests. These data can also help to carefully monitor the changing patterns and dynamics of this valuable but still largely underestimated (and underrated) resource.
Alexandre, D. Y., Lescure, J. P., Bied-Charreton, M. and Fotsing, J. M. 1999. Contribution à l'état des connaissances sur les arbres hors forêt (TOF) IRD-FAO, Orléans, France, 185 pp.
Arnold, J.E.M. 1996. conomic factors in farmer adoption of forest product activities. InLeakley, R.R.B.; Melnyk, M. and Vantomme, P. (eds.)Domestication and commercialization of non-timber forest products in agroforestry systems. Proceedings of an international conference held in Nairobi, Kenya 19-23 Feb. 1996.Vol. 9, Non-Wood Forest Products FAO , Rome.
Auclair, D., Prinsley, R., and Davis, S. 000. Trees on farms in industrialised countries: silvicultural, environmental and economics issues. InProceedings of XXI IUFRO World Congress 7-12 August 2000, Kuala Lumpur, Malaysia, p. 776.
Bernus, E. 1980. L'arbre dans le Nomad's land. In Pélissier, P., 1980. L'arbre en Afrique tropicale - La fonction et le signe. Cahiers ORSTOM des Sciences HumainesXVII (3-4): 171-176.
Boffa, J-M. 2000b. Les parcs agroforestiers en Afrique subsaharienne FAO Conservation Guide 34, FAO, Rome, 258 pp.
Brown, S. 1997. Les forêts et le changement climatique: les terres boisées comme puits de carbone. In Comptes rendus du X I Congrès forestier mondial. 13-22 octobre 1997 Antalya, Turkey. Volume 1, theme 4, 105 -114. Antalya.
El Lakany, M. H., Mehdipour Ataie, A. Murray, S., Pastuk, Rouchiche, S., Webb, R. 1999. La foresterie urbaine et périurbaine. Etude de cas sur les pays en développement. FAO, Rome. 201 pp.
FAO, 1989. Forestry and nutrition: a reference manual. Rome.
FAO, 1996a. Declaration of the World Food Summit Rome.
FAO. 2001a. Les changements climatiques et le Protocole de Kyoto COFO Document 2001/9 presented to the Committee on Forests : 12 - 16 March 2001. Rome, 5 pp.
FAO, 2001c. La situation des ressources génétiques forestières de la zone sahélienne et nord-soudanienne et plan d'action sous-régional.Topical paper FGR/2F, FAO, IPGRI & ICRAF. FAO, Rome.
Kumar, A. and Sastry, C.B. 1999. Le réseau international de recherche sur le bambou et le rotin. Unasylva 0, 198: 48-53.
Leipzig Declaration 1996. Leipzig declaration on the sustainable use of plant genetic resources for food and agriculture, 23 June 1996. Leipzig.
Ogle, B.M. and Grivetti, L.E.1985. The legacy of the Chamaleon: edible wild plants in the Kingdom of Swaziland, Southern Africa Part I-IV. Ecology of Food and Nutrition, vol. 16 and 17.
Roose, E. 1994. Introduction à la gestion conservatoire de l'eau, de la biomasse et de la fertilité des sols(GCES). Soils Bulletin 70, FAO, Rome, 420 pp.
Scoones, I., Melnyk, M. and Pretty, J. N. 1992. The hidden harvest: wild foods and agricultural systems. A literature review and annoted bibliography International Institute for Environment and Development, London.
Secretariat of the Convention on Biological Difersity. 2000. De la politique à la mise en _uvre Décisions de la Cinquième Réunion de la Conférence des Parties à la Convention sur la diversité biologique. Nairobi, Kenya, 15-26 May 2000 Secretariat of the Convention on Biological diversity, Montréal.
Unruh, J.D., Houghton, R.A. and Lefebvre, P.A. 1993. Carbon storage in agroforestry: an estimate for sub-Saharan Africa. Climate Research3 : 39-52.
Walter, A. 1996. Utilisation et gestion traditionnelles des arbres fruitiers au Vanuatu. ORSTOM, Cahiers des Sciences Humaines 32, 1: 85-104.
Watkins, C. 1998. A solemn and gloomy umbrage: changing interpretations of the ancient oaks of Sherwood forest. In Watkins, C. (ed.) European woods and forests: studies in cultural history CAB International, Wallingford.
World Bank, 1995. The World Bank Atlas Washington D.C., 36 pp.
This article was excerpted with permission of the publisher from:
Bellefontaine R., Petit S., Pain-Orcet M., Deleporte P., Bertault J.G. 2002. Trees outside forests : towards better awareness. FAO Conservation Guide 35. FAO, Rome.
This work summarizes the growing role of trees outside forests in land development, landscape management, and improvement of production and food security. The entire text of the book can be viewed at: http://www.fao.org/DOCREP/005/Y2328E/y2328e00.htm
About the Authors
34398 Montpellier Cédex 5
Sandrine Petit has a doctorate in geography from the University of
Orléans in France, has conducted research in Burkina Faso with IRD,
CIRAD and CIRDES, explored agroforestry practices in the Caribbean
Islands and Indonesia.
TA 10 / D
Campus international de Baillarguet
34398 Montpellier Cédex 5
BP 1292, Pointe-Noire
Tel : +242 94 47 95
Fax : +242 94 47 95
Research countries: Africa, Cameroon, Côte d'Ivoire, French Guiana,
Keywords: agroforestry, arid lands, biodiversity, botany, ecology,
economics, forest management