0285-B1

Variability of the Structure of Traditional Agroforestry Systems According to the Latitudinal Gradient and Local Community Practices

K. Wala^[1], A.R.A. Saliou, O. Arouna, A.K. Guelly and B. Sinsin

Abstract

The presence of trees in agrosystems is a fundamental property of agrarian landscape in tropical Africa. This study aims to define the typology of traditional agroforestry systems and show the variability of their structure in the so-called Dahomey gap (Benin, Togo and Ghana). Forest inventory and ethnobotanic investigations were carried out in several sites across the study area (Togo and Benin). The prospected sites are located at about 7° and 8° N (in the forest zone of south-west of Togo), 9° and 10° N (in south sudanian savannas zone of Togo), and 11° and 12° N (in north sudanian savannas zone of Benin). In each site, tree inventory was done in plots of 50 m × 50 m.

Three types of traditional agroforestry systems were identified: home garden and farm parkland extended across the study area, and “multistage farms” in cocoa and coffee plantations in southwest Togo.

The structure of these agrosystems varied according to latitudinal gradient and the practices of local communities. Some agroforestry species like Parkia biglobosa, Vitellaria paradoxa and Vitex doniana have a large distribution spectrum, and others were restricted to a specific climatic region. The diversity index of Shannon increased from 0.51 bits in the north to 3.27 bits in the southwest region. There is a relationship between plant diversity of parkland and selectivity of species conserved in agrosystems by local communities. Wherever this selectivity is high, the parklands are monospecific. Tree density on farms varied from 260 to 500 trees/ha in forest area, 32 to 65 trees/ha in south sudanian zone, and 15 to 26 trees/ha in north sudanian zone.

Tree species conserved in farms provide many non-timber products such as food (leaves, fruits, flowers), forage, medicinal plants, fuelwood, material for construction and craft. They are also a major source of economic income in rural areas.

Introduction

The agrarian landscape in tropical Africa has particular physiognomy according to the presence of trees conserved and keep up by the farmers. This particular physiognomy is tied to the traditional farming systems in which perennial woody species are conserved in farms with the crops and/or breeding in a dispersal spatial arrangement (Bonkoungou 1994).

Numerous studies were carried out on these farming systems in the so-called Dahomey gap (Benin, Togo and Ghana) area, but there is not a synthesis of these studies in that area. The extension of the study area on several climatic zones cover diversity of vegetation, soil, geology, hydrographic, and communities culture. This diversity of landscape and culture match with differences in farming systems across the Dahomey gap. This study aims to do a synthesis of traditional agroforestry systems and to show the variability of their structure in the Dahomey gap according to latitudinal gradient and local communities practice.

Material and methods

The studies were carried out in the Dahomey gap (Togo, Benin), which represent an interruption of the West African tropical forest at the level of the gulf of Guinea (IUCN 1992). The choice of the study sites was done so that to represent the diversity of climate and vegetation types in the Dahomey gap. Thus four sites are chosen with one in the tropical forest zone (Plateau west site), one in southern sudanian zone (Niamtougou site) and two in the northern sudanian zone (Alibori and Djona sites) (fig. 1).

Except the mountain forests of southwest of Togo (Akpagana 1992), the Dahomey gap is mainly covered by sudano-guinean and sudanian savannas.

Climate is sub-equatorial in southern, and tropical in northern. There is a geographic gradient of climate characteristics (precipitation, temperature, relative humidity). Rainfall and relative humidity increased from northern sudanian zone to forest zone but the temperature decreases from northern sudanian zone to forest zone (table 1).

Table 1: Climatic characteristics of the study area

In each site, inventories of trees in farms and fallows were done in plots of 50 m × 50 m in the sudanian zone and 20 m × 20 m in the forest zone (table 2).

Table 2: Number of plot established in study sites

Floristic data were quantitatively analyzed for abundance, density and frequency. Trees were considered to be individuals of dbh (diameter at breast height) >10 cm and sapling of dbh < 10 cm. The diversity index for all trees species in each site was computed by using Shannon-Wiever Information Index (Shannon &Weaver 1963), and the evenness index of Pielou.

To understand agroforestry practices, ethnobotanic inquiries were done at farmers level. The questions concerned the age of farms, the duration of fallows, the origin and uses of trees conserved in farms and the principal crops.

Figure 1: Study area

Results

Three types of traditional agroforestry systems were identified: home garden, farm parkland, and «multistage farms» practice in cocoa and coffee plantations in forest zone of Togo.

Home garden

There are agroforestry systems located around home met across the study area but their species composition has been studied at Niamtougou (9°50’). The species richness vary from 5 to 52 species. Numerous introduced fruit-trees are planted: Mangifera indica, Citrus spp, Carica papaya, Annona muricata, Cocos nucifera, Psidium guajava, etc. Local fruit-trees like Blighia sapida, Hyphaene thebaica, Borassus aethiopum, Zanha golungensis are also conserved in the home gardens. Another species in the home gardens are trees that organs (leaves, seeds, flowers) are used like legumes (Adansonia digitata, Ceiba pentandra, Moringa oleifera, Vernonia amygdalina, Bombax costatum, etc.) or used for forage (Ficus thonningii, F. polita, Celtis integrifolia). In the sudanian zone there are numerous fetish-trees in home garden. At Niamtougou for example we can cite Milicia excelsa, Antiaris africana, Voacanga africana, Holarrhena floribunda, Oncoba spinosa, Dracaena arborea, A. digitata, Hyphaene thebaica and Borassus aethiopum. Most of these species and others are maintained as medicinal and ornamental plants in home gardens.

Agroforestry parkland

They are met across the study area but their structure has been studied in the sudanian zone: at Niamtougou in the southern sudanian zone, and at Alibori and Djona in the northern sudanian zone. The species richness failed from 25 species in the southern zone to 18 species in the northern. The Shannon diversity index is low and varies also between the two zones. In the southern, it is about 1.97 bits at Niamtougou, but in the northern sudanian zone, it is about 0.51 bits at Djona site. The evenness of tree species decreases from 0.77 at Niamtougou to 0.19 at Djona (11°50’). The parklands are denser in south sudanian zone, (32 to 65 trees/ha) than those of northern sudanian zone that count up 15 to 26 trees/ha. Two multipurpose trees dominate the parklands in these areas: Vitellaria paradoxa and Parkia biglobosa which distribution area extended to sudano-guinean, and sudanian zones.

Some particular conditions (rainfall and socio-economic interest) could favor the development of another kind of parklands. That is the case of the sub-natural palm-grove of Niamtougou. This palm-grove is much dense and counts up to 135 trees/ha with 95.37% of palm trees. The Shannon diversity index is very low (0.34 bits) showing so the dominance of palm trees in these parklands.

Multistage farms

Introduction of heliophile varieties of coffee and cocoa in the southwest forest zone of Togo has accelerated the forest degradation. Whenever the farmers established that without tree-shade, the coffee plants died out with a decline of production, then the farmers used to return to their old practice: the multistage farm system. It consists to preserve in the cash crop plantations some natural tall trees, which will give their shade to coffee and cocoa plants. Farmers, always select shady trees for their multipurpose services. Shannon diversity index is about 3.47 bits but tree species evenness is medium (0.69). The density is about 260 to 500 trees/ha. Three groups of species constituted these agroforestry systems:

- The fruit-trees planted for their income: coffee (Coffea spp.) and cocoa (Theobroma cacao), Persea americana, Citrus spp., Cola nitida, Elaeis guineensis, etc.

- Trees which are preserved at land cleaning time: Milicia excelsa, Antiaris africana, Parinari glabra, P. excelsa, Erythrophleum suaveolens, Khaya grandifoliola, Alstonia boonei, Ceiba pentandra, Aubrevillea kerstingii, Piptadeniastrum africanum, Dialium guineense, etc.

- Those that appear after land cleaning: there are pionners like Albizia adiantifolia, A. ferruginea, A. glaberrima, A. zygia, Macaranga barteri, Harungana madagascariensis, Margaritaria discoidea, Xylopia aethiopica, etc.

Floristic and phytogeographic affinities of study sites

The floristic composition of the agrosystems varies according to their geographic situation.

The cluster analysis shows two groups of sites: the forest zone form itself one group and the another three sites forms the second group (fig. 2). That explains difference in species composition of agroforestry systems between forest and sudanian zones.

Figure 2: Study site’s hierarchical classification dendrogram

Agrosystems in forest zone (plateau) are widely dominated by guineo-cogolian species (68%) when in sudano-guinean and sudanian zones, they are dominated by sudano-zambesian species with respectively 57.85% at Niamtougou, 66.67% at Alibori and 81.82% at Djona (fig. 3). At Niamtougou, some guineo-cogolian species are present in the agrosystems certainly in home gardens.

Figure 3: Phytogeographical species spectrum of study sites

Discussion

Existence of the described traditional agroforestry systems indicate the needs of local communities to grow diverse plants species. The fundaments of this practice are numerous advantages (Nair 1984, Wala 2001) of trees conserved in farms. Effectively, these advantages explain the functional typology of parklands (Seignobos 1982): alimentary parkland dominated by Parkia biglobosa, Adansonia digitata, Ceiba pentandra, Bombax costatum which organs (leaves, flowers, seeds) are eaten; oleaginous plants parkland dominated by Vitellaria paradoxa and Elaeis guineensis; fire-wood parkland with Anogeissus leiocarpa and Crossopteryx febrifuga. We can add forage parkland with Pterocapus erinaceus, Khaya senegalensis, Ficus spp., and Afzelia africana in the northern sudanian (Arouna 2002, Saliou 2001). These types of parklands are not isolated according to their function but at farm level, a parkland share several of these functions. Farmers controlling trees density preserved several species with numerous uses, which constitute incomes for rural populations.

Another advantage of agroforestry systems is role of trees in soil improving in farms. Litter of trees constitutes fertilizer for crops. This role is well played by leguminous trees like Albizia spp. in the forest zone (Guelly 2000). Also in the sahelian zone, leguminous trees like Acacia albida are conserved in parklands to improve the soil quality (Depommier et al. 1993).

The management of trees in agroforestry systems contributes to maintain a more or less dense vegetation cover in the farming space. That has an important ecological advantage by protecting soil against erosion and favoring fast reforestation of fallows. In the forest zone among species conserved, there are pioneers (Albizia spp., Harungana madagascariensis, Margaritaria discoidea, Trema orientalis etc.), and forest trees that are seed producers (Guelly et al. 1999). In the same way, Bouquet and Debray (1974) noticed that Albizia spp. widely distributed in forest zone of Côte d’Ivoire colonize fallows and secondary vegetations.

Agroforestry systems are widely dominated by phytogeographical species that are typical to climatic zone. In the forest zone guineo-cogolian species dominate the multistage farms when in sudanian zone, parklands are dominated by sudano-zambesian species. In Sahelian zone, parklands are dominated by spine trees like Acacia alibida associated with other local species (Depommier et al. 1993). Some species like Albizia spp. Cassia spectabilis, Pycnanthus angolensis, etc. are widely distributed and conserved in various forest phytogeographical regions as in Burundi in coffee and cocoa systems (Depommier 1988). In Latin America, shady trees in cocoa plantations are dominated by local species like Cocos nucifera, Persea americana, Cedrela odorata, Cordia alliodora, Ficus spp, Tabejuga spp. Gliricidia sepium, Erythrina spp., Albizia spp., etc. (Alpizar et al. 1986). These examples show that agroforestry systems can differ in floristic composition according to local climax mainly controlled by climate and soil conditions. This proves that local communities identify useful species in their surrounding environment and then conserve and protect them in situ. Multistage farms practice occurs mainly in guineo-cogolian forest region. That system is not practiced in the sudanian zone because of water stress that not allows high density in plant community. Meanwhile, some introduced fruit-species like Mangifera indica, Citrus spp., Carica papaya, Annona spp., etc. have a widely distribution spectrum.

Some species could be described as vicariant species (Daget & Godron 1974) as they are used for the same purpose in different climatic zone. For example in the forest zone, palm trees produce oil. In the sudanian zone palm is rare so the local people rely on shee butter tree (Vitellaria paradoxa) that constitutes their main source of oil. Also in the forest zone timber trees are Milicia excelsa, Khaya grandifoliola, Erythrophleum suaveolens, Antiaria africana, when in the sudanian zone, they are Khaya senegalensis, Afzelia africana, Pterocarpus erinaceus, Diopyros mespiliformis used for the same purpose.

Difference between species composition and density of parklands in southern and northern sudanian zone could also be explained by difference in rainfall. The less density of parklands in northern is related to the low rainfall in this area. Numerous studies show that the density of parklands increases from southern to northern latitude in tropical Africa in the same manner as aridity increased. That is the case, in the sudano-guinean at Bassila (9°00' N) where Schrekenberg (1996) counted 63 trees/ha and in Ghana where tree density in farm parklands is 83 trees/ha (Hall et al. 1986). In the sudanian zone, Wala (2001) counted on average 60 trees/ha at Niamtougou (9°50' N) when Boffa (1995) counted 27 trees/ha in the south of Burkina Faso as in northern of Benin (10°50' N) where Arouna (2002) counted 26 trees/ha. These data show that differences in farm parklands tree species and density are due first to climax vegetation density as explained by latitudinal rainfall, and secondly by local farmer practices through a particular zone.

Conclusion

Results obtained show differences of traditional agrosystems structure according to rainfall gradient and local community practices. So far, the forest zone is characterized by multistage farms in which forest multipurpose trees are preserved. In the sudanian zone there are agroforestry parklands dominated by Vitellaria paradoxa and Parkia biglobosa. They still defer in their density and floristic composition according to climate and local community uses. The traditional farming systems described vary widely also within a region. The different species conserved usually have multiple uses (food, fruit, firewood, timber, windbreaks, etc.). Considering high rate of population in rural areas and land scarcity, the agroforestry systems are a good alternative for land management. Agroforestry improvement will contribute to have an adequate tree cover in farmland, and to assure food security and revenues in rural areas in the tropics.

References

Akpagana, K., 1992. Les forêts denses humides des Monts Togo et Agou (République du Togo). Bulletin du Muséum national d’Histoire Naturelle, sect. B, Adansonia, 1: 109-172.

Alpizar, L., HW. Fassbender, J. Heuveldop, H. Fölster and G. Enriquez, 1986. Modelling agroforestry systems of cocoa (Theobroma cacao) with Cordia alliodora and Erythrina poeppigiana in Costa Rica. Inventory of organic mater and nutrients. Agroforestry Systems 4:231-242.

Arouna, O., 2002. L’exploitation des ressources biologiques et la dynamique de la forêt classée de l’Alibori Supérieur (secteur de l’arrondissemnt de Bagou). Mém. Maîtrise géographie, FLASH-UAC, Cotonou, Bénin, 108 p.

Boffa, J.M., 1995. Productivity and management of agroforestry parklands in the Sudan zone of Burkina Faso, West Africa. Ph. D. Dissertation. Prudue University, West Lafayette, Indiana, USA. 101p.

Bonkoungou, E., 1994. Les parcs agroforestiers des zones semi-arides d’Afrique de l’Ouest: conclusions et recommandations du symposium international de ouagadougou. Coordination du réseau SALWA, 22p.

Bouquet, A. and Debray M., 1974. Plantes médicinales de Côte d’Ivoire. Travaux et documents de l’ORSTOM, Paris, France. n°32:232 p.

Daget, P. and M. Godron, 1974. Vocabulaire d’écologie. Hachette, Paris, France. 273p.

Depommier, D., 1988. Potentiel agroforestier des systèmes d’utilisation des sols des hautes terres d’Afrique de l’Est à régime pluviométrique bimodal, Burundi. Rapport AFRENA 17, 157 p.

Depommier, D., E. Jadonet and R. Olivier, 1993. Les parcs à Faidherbia albida et leurs influences sur les sols et les cultures à Watimona, Burkina Faso. Ed. Van. Belt, R.J. pp 111-115.

Guelly, K., 2000. Albizia spp. (Mimosaceae) dans les plantations de caféiers sur le plateau Akposso (Togo). J. Rech. Sci. Univ. Bénin (Togo), 2000, 4 (1): 84-92.

Guelly, K., H PUIG, Y.A. WOEGAN and K. KOKOU, 1999. Les formations à Harungana madagascariensis (Lam.) Ex Poir (Guttiferae) dans les jachères sur le plateau Akposso. Acte du Séminaire International La jachère en Afrique Tropicale” 13-16 Avril 1999, Dakar, Sénégal.

Hall, J.B., D.P. Aebischer, H.F. Tomlinson, E.O. Osei-Amaning and J.R. Hindle, 1986. Vitellaria paradoxa: a monograph. School of Agricultural and forest Sciences Publication n° 8. University of Wales, Bangor, Royaume-Uni. 105 p.

IUCN (Sayer J.A., Harcourt C.S. & Collins N.M. eds) 1992. The conservation atlas of tropical forest Africa. Macmillan Published Ltd.

Nair P.K.R. 1984 Soil productivity aspects of agroforestry. Science and practice of agroforestry, 120p.

Saliou, A.R.A., 2001. Mode d’occupation des terres dans le village de Boiffo et relation avec la conservation de la zone cynégétique de la Djona. Mém. Maîtrise géographie, FLASH-UAC, Cotonou, Bénin, 102 p.

Shannon, C.E. and W. Weaver, 1963. The mathematical theory of communication. University of Illinois Press, Urbana.

Schrekenberg, K., 1996. Forests fields and markets: a study of indigenous tree products in the woody savannas of Bassila region, Bénin. Ph. D. Thesis. University of London, Londres, 326p.

Seignobos, C., 1982. Végétations anthropiques dans la zone soudano-sahélienne: la problématique des parcs. Revue de géographie du Cameroun, 3: 1-23.

Wala, K., 2001. Typologie, structure et fonctionnement des agrosystèmes traditionnels dans la préfecture de Doufelgou (Nord-Togo). Mémoire DESS, FSA-UAC, Cotonou, Benin, 97 p.