Towards an animal/tree/grass combination**

J. Valenza and A.K. Diallo

Institut Sénégalais de Recherches Agrìcoles (ISRA)
Laboratoire National de IÉlevage et de Recherches Vétérrinaries, Dakar-Hann, Senegal

References

Water projects in northern Senegal have enabled the continuous utilization of vast areas of natural rangelands of the Sahelian or Sahelo-Sudanian type, thereby attracting a growing number of animals which have become settled there to a greater or lesser degree. One of the consequences has been the transformation of the landscape by trampling, overgrazing and indiscriminate trimming on the part of herdsmen. This emerges most clearly in areas around boreholes and watering points, which during the dry season are characterized by the gradual disappearance of the grass stratum. The disappearance becomes total in the immediate surrounding area, where the ligneous plant cover is almost entirely destroyed or exists only in the form of stunted, enfeebled trees and shrubs, constantly nibbled away by animals. The landscape takes on a desolate appearance, which has been aggravated by the sand-storms and drought of recent years.

Since 1975 the Service des Eaux et Forets du Sénégal has launched a pastoral reafforestation programme round the Mbidi borehole, after an initial experiment involving the planting of eucalyptus (Acacia senegal (L) Wild). The programme was intended to stimulate the development of an integrated management system for the population foci constituted by the Ferlo boreholes, using species which could adapt to the climatic conditions of the area, and following methods which remained to be defined. The programme was extended in the following years to boreholes at Tatqui, Vindou Tingoli, Labgar, etc, which are located in the sandy parts of the Ferlo.

The system was thus intended to involve not only water and grassland, but also the browse provided by ligneous plants which would be planted to provide shade for the animals, to curb wind erosion, and to improve and make more hospitable the environment surrounding the boreholes.

The reafforestation programme required the total protection of the zone planted for at least five years, prohibiting the presence of all animals, in order to succeed. One would have expected a further transformation of the grass stratum to occur as a result. In fact, up till then, trampling and manuring (faeces and urine), which increased in intensity nearer the borehole, had brought about changes in the grass stratum.

The initial observations to which it was subject had shown that this substitution pasture on sandy soil (Valenza, 1975) was qualitatively and quantitatively better. This could be seen merely by travelling round the boreholes in the sandy part of the Ferlo at the end of the wet season, when it was clear that the grass stratum was more abundant and higher, between 0.5 and 1 km, than further away, even if more so in a low rainfall year. Dry matter yields and total nitrogen content were distinctly higher.

Subsequent observations (Valenza, 1980) confirmed these yields and further showed:

a) that beyond 4/5 km the recuperation of the grass stratum was strictly dependent on rainfall;

b) the unfavourable effects of trampling were at their maximum at about 2.5 km (DM productivity was frequently minimal and density sometimes lower);

c) the nitrogen quota provided by dunging more than compensated for the unfavourable effects which trampling might have had near the borehole and promoted vegetation with an excellent feed value, which was unfortunately very little utilized since it was rapidly soiled and trampled after the end of the rains;

d) only the vegetation within a radius of 200-300 m around the watering points was really degraded, since it was highly nitrophilous and not consumed by the animals (Cassia obtusifolia L. sp. pl. and Cassis occidentalis L. sp. pl.).

A reafforestation site located between 0.5 and 1.5 km from the borehole and where trampling and dunging would be prohibited for a minimum of 4/5 years would thus have every chance of bringing about new changes in the grass stratum, which had hitherto seemed rather unfavourable.

Hence, since 1976, a series of observations has been carried out for the various reafforested boreholes, intended to monitor the development of the grass stratum in order to arrive at a definition of the optimum utilization conditions for this improved environment. Various utilization methods could be envisaged for the development zone following the obligatory prohibition period, for example:

b) opening the site to animals only at the end of the dry season; the site would then act as a reserve supply of standing dry grass, which would benefit from dunging;

c) opening the site to animals at the beginning of the dry season, after cutting the green vegetation on the site, which would still benefit from dunging;

d) closure of the site, with utilization of grass by cutting and carrying, but with the suppression of dunging and transportation of prunings.

Observations of this kind can only be carried out at Vindou Tingoli and Mbidi, where the rainfall conditions since 1976 have enabled the grass cover to recuperate, which was not the case at Tessekre and Labgar in 1978 and 1979.

Only the botanic composition could be monitored and not productivity, since the various kinds of work carried out in the reafforested parts during the first two years to ensure the success of the operation (subsoiling, weeding, disk-harrowing, etc) had led to widely differing conditions in the area, making any comparative measurement of productivity quote impossible.

However, from the botanical viewpoint, in the very first year it was noted that the flora had become richer, more particularly in species other than grasses and legumes, although there was a drop in the number of stocks to the linear metre, or in the density, (see Table 1) and in the average height of the vegetation.

Table 1. Vegetation density.

Although grasses dominate by a wide margin whatever the area and year, the species by which they were represented were no longer the same, especially at Vindou Tingoli; within the reafforested site no longer the same, especially at Vindou Tingoli; within the reafforested site there was a drop in the level of Cenchrus biflorus Roxb. and an increase in Aristida mutabilis Trin. and Rupr. and Schoenefeldia gracilis Kunth.

It is therefore likely that a drop in density, and the substitution of high-producing species by others which are less productive, leads to a net decrease in the overall herbaceous biomass. But only comparative measurements, which in all probability will be made during the next season, will really be able to indicate whether this is true.

It therefore seems likely that the suspension of the nitrogen quota supplied by faeces and urine together with the suspension of trampling, as a result of total protection of an undergoing reafforestation, leads to qualitative and quantitative changes in the grass stratum which are not very favourable. In all probability there is a case for maintaining these quotas, or at least for encouraging them during a certain part of the year, as soon as the necessary period of protection for browse plants is over. This would enable considerable amounts of grass with a good feed value to be produced. However, there is no doubt that although browse plants need to be protected for a certain period, their utilization, especially in the case of browse trees, should be managed rationally, not directly by animals but rather by herdsmen, who would prune them according to the appropriate techniques for assuring their maintenance.

A utilization plan could be as follows, once the operation has been a success; total protection of the area from July to December, with a cut taken from the grass stratum at the end of the rainy season, when the climatic conditions still enable a large quantity of hay with good protein and energy values to be harvested (cutting at the optimum mornent would involve too many risks); opening of the area to animals between January and July; these would benefit by the foliage and fruit of correctly pruned branches, and would provide manure for the following season.

Admittedly, there are many considerable problems to be overcome: how to give efficient protection to the site while enabling it to be opened or closed easily at minimum cost? Who would cut the grass and which animals would be allowed to spend some time grazing the area?

However, this kind of plan or something similar, enabling the direct or indirect utilization by the animal of a grass production, to the improvement of which it would have contributed both qualitatively and quantitatively, and of both the leaves and fruit of trees also intended to rehabilitate the environment around boreholes, would constitute an attractive tree/grass/animal combination.

References

Valenza, J. (1975). 'Les pâturages naturels de la zone sylvo-pastorale du Sahel Sénégalais, vingt ans après la mise en valeur'. In: Colloque sur l'inventaire et la cartographie des pâturages tropicaux africains. Bamako, 3–8 March, ILCA.

Valenza, J. (1980). 'Surveillance continue de pâturages naturels saheliens Sénégalais. Résultats de 1974 à 1978'. (in press). Rev. Elev. Méd. Vét. Pays Trop.