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Agro-forestry aspects of the establishment of the green belt around ouagadougou, upper volta
Peter E. Weinstabel
The Present Situation
In 1975 the German Upper Volta Forestry Project began to lay out a green belt around the capital city of Upper Volta, Ouagadougou. This ribbon-shaped plantation has an average width of more than 500 metres. It begins to the north-east of the city and is being extended annually in a north-westerly direction at an annual average rate of 120 hectares. At present 800 hectares are under cultivation, of which 720 have been afforested with rapid-growing species of trees such as Eucalyptus camadulensis (40 per cent), Azadirachta indica (30 per cent), Cassia siamea (30 per cent), Gmelina arborea (5 per cent), Dalbergia sissoo and Acacia nilotica var. adansonii. As the land had few trees it was simply cleared of the sparse secondary bush, the few old trees present (mainly Butyrospermum paradoxum and Barkia biglobosa) being retained. After the soil had been worked intensively using a crawler-type tractor (Caterpillar D7) the stand was planted at 4 by 4 metre spacing.
The land planted is traditionally considered to be part of the communal tribal land available for use by the surrounding villages. Up to 70 per cent of the soils may be regarded as red lateritic soils which are marginal for agriculture. Without intensive tilling only very meagre yields of crops are possible and relatively long fallow periods are necessary.
However, as there is a shortage of agricultural land round Ouagadougou, with a population of more than 250,000, even the marginal sites are used continuously. There is thus no opportunity for establishing forest areas unless the population derives a direct benefit from them. Benefits, from the point of view of the local people, would include the harvesting of agricultural produce over a period of several years and the possibility of paid employment in forest activities.
Functions of the Green Belt within the Context of Overall Urban Planning
The establishment of the green belt around Ouagadougou is being pressed forward for a number of reasons, above all because of its multiple functions.
Like most African cities, Ouagadougou, with an annual population growth of 6 to 8 per cent, is growing spontaneously in a disorderly manner and without any consideration for overall urban planning. Building activities are expanding every year, and the destruction of the existing rural belt around the urban areas through the indiscriminate spread of settlements is particularly evident along the main access roads. This dense settlement leaves no space for green areas, small areas of cultivation and the rehabilitation of open spaces where this is needed, for example for erosion control. If such open areas are established at a later date considerable resettlement costs will be incurred.
The idea of establishing a green belt was primarily to lay out an afforested area around the city. This green belt. in addition to separating the city centre from the new housing and industrial estates, also has the other important functions listed below.
It has a protective function in soil conservation, in reducing the impact of the dust-laden winds which blow annually from the north-east, and in restoring the habitat of the severely depleted fauna in areas close to the city. In particular its filter effect in reducing the masses of dust carried into the city by the wind would bring a marked improvement in the quality of life of the urban population.
The recreational function of a green belt is not inconsiderable. The capital city, Ouagadougou, has only a very few small green spaces scattered irregularly through the city. The town forest at present covers only 200 hectares, the remains of the natural woodland round the city water reservoir. However, during the last twenty years this has neither received sustained tending nor has it been expanded. The town forest was therefore also included in the overall plan for the green belt.
Wood production from permanent plantations is also important, since firewood and building timber are scarce and extremely expensive for the urban population. More than 30 per cent of the income of an urban family is spent solely on firewood, a fact which clearly has an effect on the frequently poor nutrition of the African family. At present the firewood needs of Ouagadougou are transported from a distance of over 80 kilometres and are sold at prices of 2,000 to 3,000 CFA francs per stacked cubic metre (stère). The average annual consumption is 0.8 cubic metres (solid) per head, and the daily requirement of the population of Ouagadougou is 400 tonnes of firewood (1 stacked cubic metre of firewood obtained from natural secondary vegetation weighs approximately 200 kg).
The expected rate of growth of the rapidly growing trees, on a rotation of seven to ten years, is between 2 and 4 solid cubic metres per hectare per annum, depending on the quality of the site. Since all the species planted can be propagated by coppicing, the trees can produce a commercial crop over three to four successive rotations.
Ground cover function: the areas selected for afforestation can, in the main, be considered as degraded areas without closed ground cover (meagre grass growth, only sporadic patches of vegetation). They are subject to severe damage from erosion and baking of the surface soil by the sun. In the rainy season in particular the top soil is constantly washed away. The afforestation of this land means that the direct radiation of the sun will be reduced, a layer of humus will be formed and the regeneration of soil flora and fauna will be encouraged. In this way it will be possible in the long term to restore the natural fertility of the soil while the risk of increasing destruction of the environment will be reduced decisively.
The effects of these measures on employment and income are of major importance. The annual growth of the workingage population in the urban settlement regions of West Africa is almost 10 per cent. The creation of at least fifty permanent long-term jobs will help to relieve unemployment and provide an increased source of income. In addition, seasonal work in planting and silviculture will provide more than 500 man-days' employment each year. The workers are to be paid 60 per cent in cash and 40 per cent in kind through the World Food Programme. The Food for Work scheme provides high protein foods (fish, oil, milk powder and the like), from which the children of the workers' families in particular will benefit.
The combination of agriculture and forestry has also the function of food supply, thus benefiting the neighbouring small farmers, especially by increasing their harvest yields. Progressive soil degradation has caused decreased production of food in many places, while the rising population requires that there should be a rapid and permanent increase in supply. In addition the combination of agriculture and forestry in one land use system prevents conflicts, so that a number of development tasks can be tackled simultaneously. Activities which are technically and economically important, but are confined to a single sector, frequently magnify conflicts between different interest groups. The result inhibits development rather than promoting it. As agro-forestry satisfies the demands of a number of sectors, it is an appropriate farming system for the West African region, and an excellent example of interdisciplinary co-operation.
The Green Belt round Ouagadougou as an Agroforestry Model
As regards right of occupancy, the Upper Volta Forestry Service has no legal title to the land required for afforestation for the "Green Belt Round Ouagadougou" project, since on the basis of traditional law the land is the common property of the village communities concerned. However, thanks to the possibility of combining forestry with agricultural crops it was possible to reach a compromise. The rights of agricultural use and the right of use of fruit and foliage (minor forest products), are still reserved to the local population, while only the subsequent logging rights fall to the Forestry Service. The afforested areas will remain legally reserved for agricultural and forestry use, thus excluding any subsequent construction development on this land. This is guaranteed by the Forestry Service as a government institution.
Following negotiations between the village authorities and the forestry officials on the tracts of land to be made available, this land is placed at the disposition of the project, without compensation, to be used for agro-forestry, in which agricultural use of the land is requested by the population and promoted by the project. In addition priority will be given to local residents when it comes to recruiting labour.
By using subsoilers to till the soil to a depth of up to 70 cm, the soils, which are frequently laterite, are loosened and their water retention capacity is increased considerably. With a rainy season lasting only three to four months (June to September) and a total precipitation of 700 mm, this is a significant measure, which more than justifies itself by increasing the percentage of natural seedings and the productivity of the land. With the spacing of trees generally used up to 1981, agricultural use of the afforested areas is possible for up to four years after planting. After this, however, it is no longer advisable as the crown canopy tends to close.
As the combined system has met with such success over the past five years, the Forestry Service is currently considering a system in which permanent farming of the land would be possible. This would involve modifying the spacing of trees to 2 metres by 7.5 metres, giving approximately the same number of plants per hectare as the old 4 metre by 4 metre spacing.
According to experience gained so far, more than 80 per cent of the people who had previously cultivated the land have continued to exercise their right to farm it. Areas not taken up by the previous cultivators are distributed by the Forestry Service to interested landless urban residents. Agreement was reached to two conditions required by the project, that an area with a diameter of 1 metre would be left clear around each of the forest plants in order to prevent excessive competition from crops, and that all the cropped areas would be tended regularly by the farmers after the seed had been sown.
Cultivation of Suitable Crops
As regards the selection of crops it was made a condition that millet varieties such as sorghum (S. bicolor) and bullrush millet (Pennisetum typhoides), should not be planted because of their suppressive effect on the trees, caused by competition for light.
The cultivation of other native crop plants was left to the free choice of the farmers, although on this point too the Forestry Service is prepared to give advice.
The experience of the past years has shown that groundnuts (arachides - Arachis hypogea) are cultivated on 39 per cent of the Green Belt areas, the average size of the fields being 1,000 m². Other species used on considerably smaller areas are okra or gombo (Hibiscus esculentus); Bambara ground-nut, or earth pea ( Voandzeia subterranea); roselle. oseille de Guinée (Hibiscus sabdariffa} which supplies leaves for pot herbs, fibres for twine, and a fleshy calyx used in soups and beverages; and cowpeas, niébé. (Vigna unguiculata and V sinensis) a native pulse.
Crops found sporadically are da or dah (Hibiscus cannabinus), the leaves of which are used as a pot herb, and which also produces a fibre; cotton (Gossypium herbaceum and other species); and millet (Pennisetum typhoides) and maize (Zea mays), despite the restrictions on their cultivation. In moist locations rice (Oryza sp.), tomatoes (Lycopersicum esculentum) and aubergines (Solanum melongena) are grown. Sesame (Sesamum indicum), which is not a traditional crop, is also grown sporadically.
Returns for ground-nuts are about 70,000 CFA francs (U.S. $250) per hectare and for gombo, used to make sauces, 700,000 CFA francs (U.S. $2,500) per hectare. Voandzeia and niébé. according to the Regional State Development Organization (ORD), give 97,000 francs (U.S. $340) and 41,000 CFA francs ((U.S.$145) respectively, after the area deducted for the production of forest trees has been taken into account.
Advantages and Disadvantages of Combined
Competition between agricultural crops and forest trees is indisputable and leads to losses in growth of the trees. However this assumes that pure forest plantations are properly tended with removal of grass competition twice after planting, and that the trees are planted at the optimal time, after approximately 150 mm of rain has fallen. Unfortunately both conditions often fail to be met, for organizational and financial reasons, so that the combined cultivation of trees and farm crops also has an undisputed advantage from the forestry point of view. Experiments dating from 1976 in the green belt around Ouagadougou have shown that. when planted in conjunction with groundnuts, the tree species Gmelina arborea and Dalbergia sissoo showed a clearly better growth at the end of the growing season when compared with trees in comparable plantations not used for agriculture. In this case the suppressive and competitive effect of the undesired grass growth inhibited the growth of the trees more severely than did the certainly more demanding ground-nut plants.
In fact experience has shown that the cultivation of groundnuts, beans and Voandzeia has a positive effect on the growth of woody plants. In particular the extra nitrogen produced by root nodule bacteria of leguminous plants has a significant, positive influence on growth. The cultivation of gombo and cotton gave less favourable results, although even in this case intercropping combined with the use of an NPK fertilizer is to be recommended. If this is applied, the tree species planted in the same plots as the agricultural crops also benefit and an increase in growth results.
To summarize, the advantages and disadvantages of combined cultivation of trees and food crops are as follows from the forestry viewpoint:
Favourable Effects of Agricultural Cultivation
- Nitrogen enrichment of the soil when leguminous plants are cropped;
- Increased water retention capacity of the soil due to frequent loosening of the top soil layer;
- Reduction of surface erosion;
- Substantial elimination of weed competition when crop areas are tended;
- Reduced fire hazard;
- Reduction of damage by browsing by domestic animals, which are kept away from the area by the local people, in order to protect their crops;
- Increased productivity per hectare.
- Root rivalry between crop plants and tree species (competition for water and nutrients);
- Depletion of nutrients from the soil through annual harvests;
- Greater susceptibility of harvested areas to wind erosion;
- Attraction of domestic animals by crop residues, leading to browsing damage to the trees wherever protective measures are lacking;
- Competition for light when tall crops are cultivated, (gombo, maize, millet).
All these investigations were undertaken from the point of view of the forester, the total net harvest returns per hectare for agricultural and forestry products not being taken into account. However there is a need for rethinking by the forestry services of developing countries. In these countries in particular the production of food has the highest priority, and to obtain self reliance in food, all possible methods of guaranteeing food supply must be fully used. Projects with an integrated approach are the only way to ensure overall development in the rural sector.
Cultivation of Indigenous Fruit and Fodder Trees
Insufficient interest has been paid in the past to the systematic cultivation of indigenous fruit trees. Plant propagation problems in the nurseries and a lack of protective measures for frequently very slow-growing trees are among the reasons why they often appear only sporadically, with young trees almost never being found. It is noticeable that the fruit trees found on agricultural land (Butyrospermum paradoxum, Parkia biglobosa and Acacia albida) are nearly always over-mature and often diseased, and only provide limited amounts of fruit and seeds.
Fruit production in subtropical and arid regions certainly should not be regarded as a "by-product" of forestry, but rather as an important way of ensuring food supplies. For this reason work began on the systematic planting of fruit trees at a wide spacing, and also along the fire break of the Green Belt. The subsequent use of the fruits, seed and foliage will be the exclusive right of the population of the neighbouring suburbs and districts of Ouagadougou, these communal rights being traditionally regulated by the Chef de Terre. We distinguish between fruit trees, which are of direct benefit to man, and forage trees and shrubs, which are used to feed cattle.
Tables 1 and 2 show the possibilities of systematic regeneration of fruit and forage trees, including the age after which a regular benefit can be derived from the trees.
TABLE 1. Fruit Trees
a Experience in other countries shows that the time to produce fruit may be considerably less than this.
TABLE 2. Forage Trees
According to an inventory of fruit trees along the green belt around Ouagadougou taken in 1981, there are on average seven fruit or forage trees per hectare. A figure of fifteen per hectare could be considered to be optimal.
Commercial Fruit Orchards
The plantation of fruit orchards on moist sites with deep soil is being encouraged by the project, although the tending and necessary irrigation for such trees during the dry period will have to be left to private initiative, especially during the first years after planting. The Forestry Service can only act in an advisory capacity in this sector and assist in the provision of plant material. The fruit tree species valued most are Mangifera indica (mango), Psidium guajava (guajava) and Citrus aurantifolia (lime). These are cultivated in groves in so-called special locations. The produce is generally sold and only small quantities are retained for domestic requirements.
However such fruit is extremely important as a source of income for the population, especially in the urban fringe belt, and thus helps to improve their welfare.
Economic Aspects of the Combination of Forestry and Agriculture, Taking the Green Belt round Ouagadougou as an Example
As an example we shall take the tree species
with the highest yield, Eucalyptus camadulensis. on a good site
with deep soil, on a six-year rotation, assuming interest at the
rate of 12 per cent annum.
from Forestry, Considering the Income
from One flotation Only'
Return from sale
of produce without
|294,000 CFA/hectare (loss);
|49,000 CFA/year/hectare (loss)
Returns from Agricultural Crops
Crops such as groundnuts, Voandzeia, cow-peas and gombo during the years 1977, 1978 and 1979, gave average returns of 107,500 CFA francs per hectare. Deducting seed costs of approximately 7.500 CFA, the net returns were 100,000 CFA francs per hectare.
Overall Economic Benefit during a Six-year
In the Green Belt the combination of agricultural crops with forest plantations increased returns considerably. Instead of forest plantations producing a deficit, a profit-earning entreprise has been created. In addition, savings to the Forestry Department in tending costs (cutting grass) are, on the average, 15,000 CFA francs per hectare per annum. These are equivalent to the labour costs for agricultural cultivation and harvesting. Hence on a six-year rotation, net returns of 50,000 CFA (U.S.$180) per hectare can be calculated.
Conclusions from Experience Gained to Date and Future Perspectives
For socio-economic reasons and its benefits to the economy as a whole, the combination of agriculture and forestry (agro-forestry) should be encouraged over large areas, in particular in the semi-arid zone. It should form an essential part of all forestry projects.
For these reasons the tree spacing used must permit permanent agricultural use without decreasing production of firewood and timber. The spacing used will depend on the climatic conditions of the zone concerned. In the case of Ouagadougou a spacing of 2 by 7.5 metres is recommended.
Further consideration should be given to the planting of fruit and forage trees at wide spacing (25 by 25 metres) to achieve a lasting, long-term improvement of food supplies for people and for cattle.
If the people in the area do not fully use the forestry green belt areas for agriculture, publicity campaigns should be mounted, particularly for the urban population, to make them aware of the possibilities.
As a result of agro-forestry the national economy will benefit from improved food and firewood supplies, and increased employment.
Kapp, G 1981 "Agroforstliche Untersuchungen am Grüngurtel um Ouagadougou." Unpublished internal project data. Von Maydell, H.J. 1978. Agroforstwirtschaft - ein Weg zur integrierten Landnutzung in den Tropen und Subtropen Entwicklung und ländlicher Raum, Vol. 6.
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