Changes of land use and vegetation near the village of Houêto
between 1981 and 1995

 

Alexander Wezel1, Brigitte Bohlinger2 and Anne Floquet3

1Department of Landscape and Plant Ecology, University of Hohenheim, 70593 Stuttgart, Germany,
Tel.: +49/711/4593628, Fax.: +49/711/4592831, e-mail: wezel@mail.uni-greifswald.de
2Department of Plant Production and Agroecology in the Tropics and Subtropics, University of Hohenheim, 70593 Stuttgart, Germany
3Department of Agricultural Economics and Social Sciences in the Tropics and Subtropics, University of Hohenheim, 70593 Stuttgart, Germany

Keywords: aerial photographs, fallow cultivation system, fallow vegetation, land degradation, urbanisation, West Africa
 
 

1 Aims of the research

Agriculture in Benin is still dominated by the fallow cultivation system. In this system fallow period is necessary for soil fertility restoration. In southern Benin, steady population growth led to decreasing fallow periods, especially in the densely populated Département de l’Atlantique (284 inhabitants per km² in 1987). Additionally, structure and species diversity of fallow vegetation is changing from shrub to grass dominated fallows. The exploitation of woody fallow species in this region for firewood and for Acadja fish rearing accelerates the degradation process. A consequence of this development often is migration towards urban centres like Cotonou or to Nigeria (Floquet and Mongbo 1998).

The aim of this contribution was to analyse the degree of land use change in a case study. Therefore, a rural area near the town Cotonou, which was one of the major experimental sites of the SFB 308, was chosen (see map 3).
 

2 Approach

2.1 Land use patterns
Aerial photographs from 1981, 1988 (November) and 1995 (March) of a region west of the village of Houêto were used to analyse land use patterns. Houêto is located about 15 km north-west of Cotonou, the largest town in southern Benin, and about 7 km west from the lagoon (Lake Nokoué) (compare map 1 of "Acadja fish rearing"). Cotonou is a fast growing town with an annual population growth of 4 % (Ministère du Plan et de la Restructuration Economique 1992). The aerial photos were geo-referenced and the land use types digitised to accomplish overlays for land use changes analysis. Land use types were distinguished visually and by field experience into seven classes: rivers, villages and settlements, grass/herb fallow, grass-bush fallow, bush fallow, plantations and sacred forests.

2.2 Vegetation
Vegetation in the southern part of Benin consists of a mosaic of forests and savannas (compare vegetation zones). Most of the original vegetation is replaced by secondary grassland or savanna due to human impact.

Information about vegetation structure and diversity of fallow land were collected from 101 vegetation surveys during the dry seasons (October to March) from 1991 to 1994. One survey consisted of several smaller vegetation plots of 2 m x 2 m regularly distributed within one site. On degraded sites, 5 plots (20 m²), on fertile sites 8-12 plots (30-50 m²) were investigated. Vegetation of each plot was surveyed with a modified method of Braun-Blanquet (1965) (details see Bohlinger 1998). The following parameters were determined for each site: total species number and frequency as well as average cover of species and vegetation groups (grasses, herbs, woody species). The average number of woody species per site was used to preclassify the vegetation data. The final classification was done manually following the plant sociological classification method of Braun-Blanquet (1965).

For most fallow sites, farmers were interviewed about land use history, cropping intensity (ratio cultivation/fallow), cultivation practices (hoeing, dikes) and fire (intensity and frequency). Main crops in the study area were maize and groundnut.
 
 

3 Results and Interpretation

3.1 Growing urban areas
The area between Houêto, Abomey-Calavi and Godomé (overview - map 3) has been subject to enormous changes since 1981. The town area of Abomey-Calavi was strongly expanding towards Houêto in the west. This is shown by a comparison of aerial photographs from 1988  and 1995 . The same can be stated for the town area of Godomé which is strongly growing in north-western direction. In 1981, the rural area between these three sites was still characterised by bush fallows and fields (picture of 1981). Until 1995, many houses and farms were built, dispersed over the whole area, with a certain concentration along roads or newly constructed secondary roads (map 1 - 1995 and map 2 - 1988).
Different causes led to this development. One cause is the geographical location of Cotonou. In the north it is limited by Lake Nokoué, in the south by the Atlantique Ocean. So only an expansion to the east or west is possible. The eastern area of Cotonou along the coast is dominated by growing industrial areas. Also, this area is a lagoon and swamp area where the water table is high during the rainy season so that the people like better housings on the plateau. Thus, the west and north-west periphery is most attractive for settling of the growing population of Cotonou. The location of the National University (UNB) and the International Institute for Tropical Agriculture (IITA) north-west of Godomé obviously accelerates the process of urbanisation. In addition, the main road to northern Benin and the railway to central Benin passes in the west of Lake Nokoué.

3.2 Land use change from 1981 to 1995
Another reason for land use changes, besides the expanding town areas, is a degradation of the economical situation of the people in the Houêto area (Floquet and Mongbo 1998). Soil fertility decreased to an extend that a surplus of staple food cannot  be achieved anymore. This was followed by different strategies of the local people: migration, orientation towards off-farm activities, pillage of fallows for wood and Acadja, and last but not least land sale to neo-rural persons. This is reflected by the land use change  (map 1 - 1995 and map 2 - 1988). In general, many bush fallows have disappeared since 1981, grass-bush fallows increased. In certain areas it was only a change from bush to grass-bush fallow and vice versa which is typical for the dynamic of the fallow cultivation system in this region. In contrast, grass fallows decreased. This might be due to low soil fertility of most grass fallows (Bohlinger 1998). On these sites, crop production is not profitable anymore. Also, production of certain woody species for Acadja or firewood is often too low, so that bush islands could regenerate on the grass fallows, if stumps of woody species were still existent. Sacred forest areas were more or less left untouched in the study area.

Vegetation dynamics can be related to farmers’ strategies (Floquet, 1994). In Houêto, a majority of autochthonous farmers mostly engage in off-farm activities and farm extensively (see Figure 1). They only crop a plot for less than four years with a maize-cassava rotation and then let it turn to fallow. Fallow is long because they wait for palms to be old enough for a wine harvest. A minority of settlers farm very intensively although in the first decades of the century they had been given grass-bush fallow. Part of their farms lay under continuous cropping with groundnut based rotations cultivated on ridges and short grass fallows. The other part is under palm, first associated with crops then with bush fallow.

3.3 Development of fallow vegetation in relation to land use intensity
The fallow types as classified with the aerial photographs can be further distinguished by their species composition (see Table 1). The bush fallow communities were characterised by their high diversity of woody species (photo 7, photo 4), whereas in grass fallows a few grass species such as Andropogon, Imperata and Hyparrhenia dominated (photo 5, photo 6)(for details see Bohlinger 1998). The different fallow communities can be seen as indicators of increasing degradation from bush fallows (I) to grass fallows (III) in dependence of cropping intensity and influence of fire (compare Figure 2). If cropping intensity is increased, bush fallows (I) will change to grass-bush fallows (II) because certain woody species are not able anymore to regenerate if they are cut too often or if bush fire for field clearing or unintentional bush fires are too frequent. If intensity of cropping and frequency of fires is very high, the physiognomy of the fallows will turn to grass fallows (III) where almost no shrubs or only fire resistant species (e.g. Annona senegalensis) are left.
 

4 Conclusions

Two main reasons for land use changes in the Houêto region can be stated. The first is decreasing soil fertility because of overexploitation of agricultural land. Many bush fallows disappeared because fallow periods were being reduced, whereas grass-bush fallows increased. Today, the Houêto region is not further able to produce a surplus of staple food. The economical situation of the people worsened, followed by the migration of local people, an orientation towards non farming activities and the pillage of fallows for wood and Acadja. Particular the sale of land to neo-rural persons and the expanding town area of Cotonou with the construction of houses and farms along roads and newly constructed secondary roads are the second main reason for drastic land use changes. The area will develop towards suburban settlements with low agricultural activities, where bush fallows are strongly reduced or not existent anymore and where cropping is only possible with high inputs of organic and inorganic fertilisers. Part of the refuses and garbage from urban areas are already being composted and this should be a source of nutrients replacing the disappeared fallows. Crop diversification, especially vegetable production, could be a possibility for farmers improve their own economic and the site conditions, as vegetables are cash crops and a growing demand is to be expected.
 

5 References

Bohlinger B. 1997. Die spontane Vegetation in traditionellen Anbausystemen Benins - ihre Bedeutung und Möglichkeiten des Managements. Plits 16 (1), W. und S. Koch Verlag, Stuttgart, 175 pp.

Braun-Blanquet J. 1965. Plant sociology - the study of plant communities. Hafner, London.

Floquet A. 1994. Dynamique de l’intensification des exploitations au sud du Bénin et innovations endogènes. Un défi pour la recherche agronomique. Dissertation, Stuttgart, University of Hohenheim. 330 pp.

Floquet A., Mongbo R. 1998. Des paysans en mal d’alternatives. Dégradation des terres, restructuration de l’espace agraire et urbanisation au bas Bénin. Margarf Verlag, Weikersheim, Germany, 190 pp.

Ministère du Plan et de la Restructuration Economique 1992. Deuxième recensement général de la population et de l’habitation. Cotonou, Benin.

6 Further Readings
Adjakidje V. 1984. Contribution à l’étude botanique des savanes guinéennes de la République Populaire du Bénin. - Thèse du troisième cycle, Université de Bordeaux III, Bordeaux, 284 p.

Menaut J.C., Cesar J. 1982. The structure and dynamics of a West African Savanna. in: Huntley BJ, Walker BH [ed.]: Ecology of Tropical Savannas. pp 80-100, Springer, New York.

Weinzierl S. 1997. Acadja - ein traditionelles, extensives Fischzuchtsystem in den Lagunengewässern Westafrikas - und seine Bedeutung für die Brachevegetation in Benin. - Master thesis, University of Hohenheim, unpublished, XVII + 84 S.
 

7 Related Websites

Ker, A. (1997): Farming Systems in the African Savanna. A Continent in Crisis. International Development Research Centre, Ottawa, Canada.

Facts About the Republic of Benin

Plans des principales villes du Bénin et Cartes du Bénin

Article sur le Bénin tiré de l'Encyclopédie Microsoft Encarta 98
 

8 Annotations

Figure 1: Farmers’ strategies and land use patterns in Houêto

Figure 2: Development of fallow vegetation in the Houêto region, southern Benin

Table 1: Fallow plant communities in the region of Houêto, southern Benin

Map 1: Land use map of Houêto 1995

Map 2: Land use map of Houêto 1988

Map 3: Overview map of the area of Houêto and Abomey-Calavi
 

9 Data Links

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