The role of browse in the Sahelian and Sudanian zones**

H.N. Le Houérou

       Principal Scientist 
International Livestock Centre for Africa

1. Introduction

Bioclimatic Classification of the Sahelian and Sudanian zones

3. The main plant formations

3.1 Vegetation in the southern and central Sahara

3.2 The steppes of the Saharo-Sahelian zone

3.3 Mimosoideae and annual grass-scrub of the Sahelian zone

3.4. The Combretaceae savanna in the Sudano Sahelian zone (400 < 600)

3.5. The northern Sudanian savanna (600 < R < 800)

3.6. The southern Sudanian savanna (800 < R < 1200)

4. Browse species

4.1 General

4.1 Main species

4.2 Secondary species

4.3 Common woody species, not usually consumed

5. Forage production of browse species

5.1 Individual production of trees and shrubs

5.2 Production from plant association

6. Browse plantations in Sahelian and Sudanian zones

7. Biology multiplication utilization

Propagation by cuttings

8. Development of Sahelian ligneous populations, and middleterm consequences

9. Shade, a screen function

10. Other uses

11. Towards an ecological management of the Sahelian ecosystems

References

1. Introduction

Forage trees and shrubs play an essential and multiple role in the balance of the Sahelian and Sudanian ecosystems exploited by man and his animals. This role becomes more important as the dry season grows longer, and decreases as the mean annual rainfall increases. It therefore grows less important from north to south according to the rainfall gradient, which is about 1 mm per km, or 110 mm per each degree of latitude.

The main contributions of ligneous species to the lives of people and animals in the Sahelian and Sudanian zones are:

b) to produce firewood and charcoal, which represent over 90% of the energy consumed by Sahelian and Sudanian populations;

c) to supply wood for building and fencing;

d) to produce wood and fibre for making tools and utensils;

e) to produce fibres for clothing, wickerwork, rope and other uses;

f) to produce various foodstuffs for human consumption (fruit, spices, fat, etc);

g) to produce medicines, dyes, tannin and other material;

h) to provide shade and act as a micro-climate for plants, animals and soils and to prevent wind and water erosion;

i) to provide a means of increasing or maintaining soil fertility and productivity and the long-term balance of highly sensitive ecosystems.

However, trees and shrubs are seriously threatened, especially in the Sahelian zone, owing to the combination of a number of natural and anthropogenic factors:

b) the fast growth of human and animal populations, leading to overexploitation;

c) the tendency of previously nomadic or transhumant populations to become sedentary leading to a constantly increasing pressure by man and his animals;

d) the development of bush-clearing and the fast growing expansion of cultivated areas; 

e) the reduction or total disappearance of fallows with the result that browse is gradually eliminated from cultivated areas (except in the traditional well-balanced agro-pastoral or agro-forestry systems, such as those with Acacia albida, the shea butter tree (Butyrospermum paradoxa) nere (Parkia biglobosa), Borassus palm (Borassus aethiopum), baobab (Adansonia digitata) etc., which are usually found in the Sudanian zone).

From a strictly pastoral point of view, and with no supplementation being given, browse should represent at least 20% of livestock diets during the dry season in the Sahelian and northern Sudanian zones. Ideally the ration should reach 30%. These feeding requirements correspond to densities of 200 to 2000 browse trees shrubs per ha, i.e. a plant cover of 525% of the land surface, depending on rainfall and grass cover productivity.

The healthy management of Sahelian and Sudanian ecosystems thus depends on the action taken to maintain the balance between:

b) trees, shrubs and undershrubs¹;

c) the various ranges of ages within each specific population, so as to maintain a well-balanced and perennial vegetation cover.

¹shrub = a ligneous plant with only one trunk at the base and generally bearing low branches having a height less than 5 m; undershrub= a ligneous plant with a multiple trunk at base and a size ranging from 1-5 m.

Browse tree/shrub stands offer a real opportunity for upgrading the soil and improving micro-climates and livestock production conditions, particularly in the Sudanian zone. These techniques, currently well-advanced in the Mediterranean arid and subhumid zones, have only rarely been investigated and tested in the tropics until now, except for experiments with Acacia albida in West-Africa and A. Senegal in Sudan.

More effective research should be undertaken in the following fields;

b) browse nutritive value and utilization for animal feeds;

c) establishment management and utilization of native and exotic species plantations and their integration into pastoral and agro-pastoral systems.

Table 1. Shows the detail of the various tropical climates

Zones	Sub-climates	Ecological Zones	Rainfall	Length of the dry season (in months)
7	Desert	Saharo-Sindian	R < 100	RS Σ 1
6b	Arid	Saharo-Sahelian	100 < R < 200	1 < RS < 3
6a	Arid	Sahelian s.s.	200 < R < 400	2 < RS < 4
5	Semi-arid	Sudano-Sahelian	400 < R < 600	3 < RS < 5
4	Subhumid	North-Sudanian (& South-Miombo)	600 < R < 800	4 < RS < 6
3	Humid	South-Sudanian (& North-Miombo)	800 < R < 1200	5 < RS < 7
2	Very humid	North Guinean North Congolese	1200 < R < 1500	7 < RS < 10
1	Pluvial	South Guinean South Congolese	1500 < R	10 < RS

Table 2.Tropical climates: distribution of livestock, vegetation and land use

Zone	Sub-climate	Vegetation	Animals	Land use
7	Desert	Punched vegetation Perennial grasses	Camels, goats, some sheep	Long-range nomadism, no crops without irrigation
6b	Arid	Evenly spread vegetation perennial grasses— Mimosoideae scrub in low-lying areas	Camels, goats, sheep, cattle during rainy season	Nomadism and transhumance. no crops without irrigation
6a	Arid	Evenly spread vegetation —Mimosoideae and animal grass shrub	Cattle (zebu), sheep, camels	Transhumance, a few subsistence millet crops
5	Semi-arid	Savanna with Combretaceae and annual grasses; some perennial grasses in lowlying areas	Cattle (zebu) sheep, goats, a few camels	Transhumance, sedentary agriculture — millet, cow pea fast-growing, groundnuts, no fodder crop
4	Sub-humid	Savanna and open woodland with Khaya, Parkia, Butyrospermanus and Andropogon gayanus	Cattle (zebu) sheep, goats	Sedentary agriculture and transhumance herds. Millet, Sorghum, Groundnuts, cowpea fodder crops and sowr pastures possible
3	Humid	Open woodland and savanna, with Daniella, Uapaca, Crosopterix, Isoberlinia Burbea-Gardenia, Perennial grasses: Hypenthelia, Andropogon	Cattle (zebu and taurine) sheep and goats. Moderate Glossina infestation	Sedentary agriculture Sorghum Groundnuts, Cotton, Maize, Tobacco, Sweet potatoes, Cassava, Mangoes, Cashew nuts, pasture and fodder crops. Husbandry limited by Trypanosomiasis
2	Very humid	Forest, derived savanna with perennial grasses Panicum maximum	Cattle (trypanotolerant taurine) trypanotolerant dwarf sheep and goats; considerable Glossina infestation	Nearly all tropical crops: Sorghum Maize Cassava, Yam, Banana, Sugar Cane, Rice, Coffee Timber production: little animal production (Trypanosomiasis)
1	Pluvial	Rain forest	A few trypanotolerant cattle and dwarf goats	Oil palm, Hevea, Cocoa, Coffee, Timber production

There can be no doubt that rational management of Sahelian and Sudanian savanna involves priority action consisting of three interdependent measures:

b) a disease control input;

c)  reforestation.

Bioclimatic Classification of the Sahelian and Sudanian zones

The Sahelian and Sudanian zones cover a belt which is 1000 to 1200 km wide and 6000 km long. It lies south of the Sahara, crossing the African continent from the Atlantic Ocean to the Nile Valley. Rainfall ranges from 100 mm on the verge of the Sahara to more than 1200 mm on the border of the Guinean zone. Isohyets run in an E. W. direction nearly parallel to the equator, with a mean inclination of 1.8° (4%) towards the south east, so that each isohyet is 2.0° or 220 km further south on the Nile Valley side than on the Atlantic coast (the 100 and 1200 mm isohyets are on the latitudes 10-18 °N in the west and 8-16°N in the east respectively).

Most ecologists and bioclimatologists have now agreed, on the whole (with a few minor qualifications), to the following classification (Koeppen,1931; Chevallier, 1933; Trochain, 1940, 1952,1969; Aubreville, 1949; Keay, 1959; Rodier, 1964; Boudet, 1970; Le Houérou, 1976, 1977; Le Houérou et al, 1980): the zone as a whole is characterized by a tropical climate with a monomodal rainfall regime and one dry season, contrasting with the Guinean and Congolese zones further south, which are characterized by an equatorial climate with a bimodal rainfall regime and two dry seasons, or no dry season at all.

It is worth noting that there is a semi-arid and subhumid equatorial enclave in the Gulf of Guinea in the coastal and subcoastal zones of Ghana and Togo, with rainfall of 500-800 mm (Accra, Lomn) and a 4–6 month dry season. This anomaly is caused by cold sea currents and "Upswelling" phenomena on this part of the coast in the Gulf of Guinea. As regards browse, this atypical zone is characterized by the following species (R. Rose-Innes et Mabey, 1964): Antiaris africana (Moraceae), Baphia nitida (Fabaceae), Capparis erythrocarpos (Capparidaceae), Capparis thonningii (Capparidaceae), Dichapetalum guineense (Chailletiaceae), Fragara xanthoryloides (Rutaceae), Grewia carpinifolia (Tiliaceae), Griffonia simpliciflora (Casalpiniaceae), Milletia thoningii (Fabaceae), Ritchie reflexy (Capparidaceae), Tiliacora warneckii (Menispermaceae).

to which can be added the following grasses:
Andropogon canaliculatus, Botriochloa intennedia, Brachiaria falcifera, Ctenium newtroni, Heteropogon contortus, Schizachyrium schweinfurthii, Schizachyrium semiberbe, Setaria sphacelata, Sporobolus pyramidalis, Vetiveria fulvibarbis.

3. The main plant formations

3.1 Vegetation in the southern and central Sahara

(R < 100 mm) is characterized by perennial bunched vegetation located along watercourses. A number of trees/shrubs used to varying degrees for browse are found along wadis, in lower areas and on cliffs: Acacia raddiana, Acacia ehrenbergiana, Capparis decidua, Pergularia tomentosa, Cornulaca monacantha, Nucularia perrini, Artemisia tilhoana, Salvadora persica, Ziziphus saharae, Solenostemma argel, Moringa peregrina, Maerua crassifolia, Balanites aegyptiaca, Ochradenus baccatus, Aerva persica, Traganum nudatum, Olea lapperini, Ficus salicifolia, Grewia tehax, Tamarix sp. pl., Calotropis procera, Leptadenia pyrotechnica.

Among these browse plants a few perennial grasses may be found:

Panicum turgidum, Stipagrostis pungens, Lasiurus hirsutus, Pennisetum dichotomum, as well as many annual ones after the rains which form the "aacheb", known also as "ghizou" in northwestern Sudan.

3.2 The steppes of the Saharo-Sahelian zone

Are very similar to the vegetation found in the Saharian wadis. However, the vegetation of the steppes is evenly spread unlike the latter. The main browse species are:

Acacia tortilis subsp. raddiana, Acacia ehrenbergiana, Grewia tenax, Salvadora persica, Leptadenia pyrotechnica, Maerua crassifolia, Cordia sinensis, Boscia senegalensis, Capparis decidua, Balanites aegyptiaca, Hyphaene thebaica.

Perennial grasses are important:

Panicum turgidum, Cympopogon proximus, Aristida pallida, Lasiurus hirsutus, Aristida papposa, Aristida longiflora, as well as a desertic psammophileous Cyperaceae: Cyperus conglomeratus.

Here and there, on shallow soils, traces remain of stands of Chrysopogon sucheri and Cenchrus ciliaris (Adrar, Air, Dj. Mara).

3.3 Mimosoideae and annual grass-scrub of the Sahelian zone

(in the strict sense) (200 < R < 400) is a very open formation where trees and shrubs predominate:
Acacia tortilis subsp. raddiana, Acaia ehrenbergiana, Acacia laeta, Acacia senegal, Balanites aegyptiaca, Ziziphus mauritiana, Acacia nubica (Sudan), Acacia mellifera (Sudan).

Lower areas subject to flooding and areas around ponds have been invaded by species of a more Sudanian type:
Feretia apodanthera, Acacia ataxacantha, Lannea acida, Dalbergia melanoxylon, Amogeissus leiocarpus, Mitragyna inermis, Terminalia avicennoides, Hyphaene thebaica, Maytenus senegalensis.

Grass cover is dominated by annual grasses, among which the main species are:

Aristida mutabilis, Aristida funiculata, Aristida adscensionis, Dactyloctenium aegyptium, Shoenefeldia gracilis, Eragrostis tremula, Cenchrus biflorus, Cenchrus prieurii.

3.4. The Combretaceae savanna in the Sudano Sahelian zone  (400 < 600)

is characterized by the predominance of deciduous mesophyllic shrubs of the Combretaceae family:
C. glutinosum, C. nigricans, C. ghazalense, Terminalia avicennoides, C. molle, C. micranthum, C. aculeatum, Guiera senegalensis, Anogeissus leiocarpus.

to which Sahelian elements are added such as:

Cadaba farinosa, Cadaba glutinosa, Grewia bicolor, Commiphora africana, Balanites aegyptiaca, Acacia senegal, Acacia laeta, Piliostigma reticulata, Bauhinia rufescens,

together with Sudanian infiltrators such as:

Acacia seyal, Acacia sieberiana, Sterculia setigera, Borassus aethiopum, Sclerocarya birrea, Bomba costatum, Pterocarpus lucens.

Table 3.Climatic distribution of browse species in the Sahelian and Sudanian zones

^aIntroduced species:

+ Species common in the zone under review

(+) Species rare or located only in particular spots (humid low areas with shallow soils and very dry environments)

The grass cover consists primarily of annual grasses:
Aristida mutabilis, Cenchrus biflorus, Andropogon pseudapricus, Ctenium elegans, Elionurus elegans, Schoenefeldia gracilis, Diheteropogon hagerupii, Loudetia togoensis, Pennisetum pedicellatum, Schizachyrium exile.

Lower and damper areas support a few perennial grasses:
Andropogon gayanus, Panicum anabaptistum, Cymbopogon giganteus, Vetiveria nigritana, Eragrostis barteri, Vetiveria fulvibarbis.

3.5. The northern Sudanian savanna (600 < R < 800)

is characterized by a relatively high tree and shrub cover averaging 2–0 to 50% and the predominance of mesophyllic browse species:
Khaya senegalensis, Bombax costatum, Borassus aethiopum, Pterocarpus erinaceus, Burkea africana, Bridelia ferruginea, Butyrospermum paradoxa, Parkia biglobosa, Piliostigma thonningii, Tenninalia avicennoides, Detarium microcarpum.

Perennial grasses provide substantial cover:
Andropogon gayanus, Andropogon ascinodis, Andropogon tectorum, Hyperthelia dissoluta, Hyparrhenia smithiana.
as well as the same annual grasses as found in the Sahelo-Sudanian zone:
Diheteropogon hagerupii, Loudetia togoensis, Pennisetum pedicellatum, Andropogon pseudapricus, Ctenium elegans.

3.6. The southern Sudanian savanna (800 < R < 1200)

is characterized by a more substantial tree cover and the infiltration of species related to the Guinean zone. Among the typical tree and shrub species, the following can be mentioned:

Tertninalia laxfliora, Terminalia macroptera, Lannea acida, Burkea africana, Bridelia ferruginea, Crossopteryx febrifuga, Anogeissus leiocarpus, Pericopsi laxiflora, Gardenia erubescens, Uapaca togoensis, Daniellia oliveri, Isoberlinia doka.
and among perennial grasses:
Andropogon gayanus, Andropogon tectorum, Andropogon ascinodis, Hyparthelia dissoluta, Dihetoropogon amplectens, Loudetia simplex

4. Browse species

4.1 General

For many reasons it is often difficult to determine a browse species. These reasons may relate to the phenological stage of the plant, season, to the feeding habits and physiological condition of the animals, to herd composition or the composition of available pasture, to grazing pressure, or to whether the browse species concerned is abundant or rare, etc. As a result different or contradictory indications can be found between the various authors, as well as sometimes between different publications by the same author.

At a first step, woody species can be classified in three broad categories:

b) species never consumed;

c) species consumed to a greater or lesser degree according to circumstances.

The species in the first two classes are the fewest (about 50 in each group); those in the third group are by far the most numerous, and in the Sahelian and Sudanian zones a hundred or so common species can be counted.

It should be noted that the nutritive value is totally independent of palatability and quantities consumed, a situation which makes an accurate estimation of the real browse value of a plant difficult, since the quantities consumed are usually not known for the area under review. Some species, such as Boscia senegalensis are extremely rich in nitrogenous elements, though little consumed. Others such as Combretum aculeatum, Grewia tenax, Stereospermum kunthianum or Oxytenanthera abyssinica are highly palatable, especially in their early stages, despite a lower or even very poor nutritive value. Some species with a good nutritive value as regards their chemical composition are totally neglected, such as Calotropis procera.

In the following list, browses have been classed in two categories: main and secondary species.

The main species are considered by most authors either as good browse, palatable to most animals, widely distributed geographically and common through most of their distribution area, or else as introduced or native species of real interest for planting as forage reserves.

The secondary species are either occasionally consumed by livestock, or restricted to a small area, or quite rare, thus contributing only marginally to livestock feeds.

4.1 Main species

Burseraceae

Commiphora africana is a typical Sahelian species that can be found in the arid zones of eastern and southern Africa and even in India. It is browsed a great deal for a few weeks at the end of the dry season and at the onset of the rains, on account of its early foliation. But its leaves fall off as soon as the rains are over. Its nutritive value ranges from average to good (814%) crude protein; 0.15 to 0.81% phosphorus, with a slightly high Ca/P ratio: 5 to 6). For more information about Commiphora africana, see Poupon (1977) and Clanet and Gillet (1980).

Capparidaceae

The Capparidaceae family contains the best browse in tropical Africa owing to its high protein and silica-free mineral content. Many of these species are highly palatable to most domesticated and wild herbivorous animals. Among the best species, the following Sahelian ones should be mentioned:
Maerua crassifolia, Maerua angustifolia, Crataeva adansoni (C. religiosa), Boscia salicifolia, Cadaba farinosa, Cabada glutinosa, Cadaba rotundifolia, Capparis decidua.
and the Sudanian species:
Maerua oblongifolia, Maerua angolensis, Ritcheia reflexa, Capparis corymbosa, Capparis tomentosa, Capparis erythrocarpos.

The main composition are as follows (Le Houérou, 1979):

Crude protein 21% (9–34)
Mineral protein 21% (8–28)
P. 0,11% (0,04–0.17)
Digestible protein/FU 180 (93–281)
Net energy 5.6 MJ (4.0–6.9)

The same characters can be found in slightly different species in the arid and semi-arid zone of East Africa (Le Houérou et Corrà, 1980):

Boscia minimifolia, Boscia albitrunca, Boscia coriacea, Maerua parvifolia, Maerua triphylla, Cadaba farinosa.

Pastoral research and experimentation in the Sahelian and Sudanian zones should give priority to the domestication and multiplication of these species. The state of knowledge on these plants is very poor as regards their biology, growth, productivity and utilization potential. Some of the least palatable such as Boscia senegalensis, have a very high protein content (30%), the equivalent of many local concentrates. Others, such as Cadaba farinosa, contain as much as 30% non siliceous minerals, thereby providing an effective "salt cure". They may be an important source of trace-elements in animal feeding but this factor has not been investigated.

Combretaceae

Among the many representatives of this family, only C. aculeatum should be classified as a main species due to its palatability, its large distribution area and its abundance. This somewhat tendrilous undershrub has been tested for multiplication in plantations. The trials have been promising in the Sudano-Sahelian zone: the germination ratio is quite high and the cutting capacity is good. The nutritive value is also good (Le Houérou, 1979):

Crude protein 16% (7–30)
Minerals 10% (7–12)
P 0.23 (0.10–0.50)
Digestible protein/FU 137 (45–298)
Net energy 5.6 MJ (4.6–6.3)

Combretum aculeatum regenerates vigorously when protected from overbrowsing. Its rather high germination rate (60–80%) and easy multiplication from root stock make this species a favourable future prospect for planting as browse hedges in the Sahelian and northern Sudanian agricultural zones.

Leguminoseae

Cesalpinioideae

Afzelia africana is a Sudanian species found in wooded savanna, frequent on gravel soils. Foliation occurs at the beginning of the second half of the dry season, in February (Toutain,1980). Young leaves are palatable to cattle and offer a good forage value (Le Houérou, 1979):

Crude protein 14% DM (12–18)
Net energy 4.5 MJ (3–6)
Digestible protein/FU 160 (100–195)
P 0.16

Branches are pruned by shepherds to make them available to animals. This species is able to produce tall trees with timber which is valued by foresters.

Griffonia simpliciflora is a shrub 1-4 m high, found in the derived savanna and fallows in the subhumid Guinean zone, with a rainfall range of 600-1000 mm and an annual dry season of 5-6 months, and common in the coastal and subcoastal plains of Ghana and Togo. It is often associated with Macroterme termitaria (Rose-Innes, 1964). This species is largely used by the local trypanotolerant humpless dwarf cattle (West African Shorthorns) under the traditional production system, especially on the Accra plain (Rose-Innes, ibid).

The utilization of this species by local cattle has been the object of detailed studies over several years (Rose-Innes and Mabey,1964–1966). It can be concluded that Grdffonia simplicifolia is an excellent browse species which compares favourably with the best classical fodders:

Crude protein 18% DM
Net energy 5.7 MJ kg DM
Dig. value DM 69%a
DM intake 2.43 per 100 kg liveweight
Crude protein D value = 81%^a
Mabey and Rose-Innes, 1964.

Daniella olivieri is a tree species of the Guineo-Sudanian savanna. Its shoots are frequently found on fallow land. The young leaves and twigs are very palatable and represent an excellent browse (Toutain, 1980; Le Houérou, 1979):

Crude protein 15% DM (8–23)
Net energy 5.4 MJ (3.4–7.0)
Digestible protein/FU 120 (65–190)
P 0.25 (0.16–0.42)

Bauhinia rufescens is a Sudano-Sahelian shrub or undershrub, reaching deep into the north Sudanian zone. It can be found on widely differing types of soil. Leaves are consumed by small ruminants and to a smaller extent by cattle. The fruit is consumed by all herbivorous animals especially, while green: Seeds have an average germination rate (30-50%) after hot water treatment).

Bauhinia rufescens is extremely resistant to browsing, produces large amounts of seeds for a long period during the dry season and regenerates vigorously when protected from browsing. It appears to be a real asset in terms of artificial regeneration, for establishing hedges between fields and on Sahelian and Sudanese fallows, together with Combretum aculeatum and Ziziphus mauritania. It has a good nutritive value (Le Houérou, 1979):

Crude protein 13.5% DM (11–17)
Net energy 5.4 (3.2–7.1)
Digestible protein/FU 0.19 (0.15–0.27)
Digestibility DM (leaves) 51.0% (Dicko-Touré, 1979)

Tamarindus indica is a Sudanian tree which spreads into Sahelo-Soudanian zone, where it is sometimes planted on account of its dense shade (a palaver-tree) and the quality of its fruit. The latter is made into a pleasant, laxative and refreshing drink. Leaves are moderately palatable when fresh, but only to small ruminants. The fruit is palatable to all animals and to man. Leaves and fruit have an average nutritive value:

Crude protein 11% DM (5–25)
Net energy 6.9e MJ (6.6–7.4)
Digestible protein/FU 81 (23–204)
P 0.07 (0.04–0.10)

Fabacoideae (or Papilionoideae)

Baphia nitida is a 1–4 m high shrub of the Guinean subhumid zone in Ghana, with mean annual rainfall of 600-900 mm and a 5-6 month annual dry season (Rose-Innes and Mabey, 1964). It grows preferably in damp low-lying areas and where termiteries are plentiful. Its frequency increases in secondary forests as rainfall rises. The forage value of this species is very good (Rose-Innes and Mabey, 1964):

Crude protein 21%
D value 54% DM
Net energy 5.7 MJ kg DM
P 0.13% DM

Digestibility DM 53.8%
A related species, B. bequaertii, represents one of the best and commonest browse species of miombo in Zambia (Lawton, 1968, 1980), with 22% crude protein and 0.3% P.

Milletia thonningii is a 10 m high tree found in the Guinean subhumid zones, on coastal and subcoastal plains in Ghana where rainfall reaches 600-1000 mm and there is a 5–6 month annual dry season. It can be found in association with Macroterrnes termitaria in secondary open formations, where it grows in clumps (Rose-Innes and Mabey, 1964).

Nutritive value:
Crude protein 19% DM
Net energy 4.9 MJ kg DM
Digestible protein/FU 201
P 0.10

Pterocarpus lucens, P. erinaceus, P. santaloides. The first of these species is Sahelian, the second one Soudanian and the third Guineo-Sudanian. These three represent an excellent fodder often sold at market during the dry season for feeding or fattening sheep, dairy cattle and prestige animals (horses).

Fallen leaves are palatable to cattle and other domesticated herbivorous animals. Trees are often pruned and lopped. Unfortunately the leaves fall quite early in the first half of the dry season. But pruning can make the foliage phenophase much longer (Cissé, in Hiernaux et al, 1979). The nutritive value is virtually the same for the three species:

Crude protein 15% DM (10–12)
Net energy 5.2 MJ (2.9–7.2)
Digestible protein/FU 135 (70–240)
P 0.15 (0.08.0.27)

Unfortunately P. lucens regenerates very poorly in the Sahelian zone, seed germinability averaging zero despite the various treatments applied.

Lonchocarpus laxiflorus is a small tree of the Sudanian savanna, the leaves of which are very palatable to animals; the fodder values are similar to those of Pterocarpus, but very few analyses are available:

Crude protein 18% DM
Net energy 4.8 MJ
Digestible protein/FU 191
P 0.13

Mimosoideae

Acacia tortilis subsp. raddiana, Acacia tortilis subsp. tortilis. The second sub-species does not exist in the western Sahel, but only in Sudan and East Africa.

The species as a whole is common in the arid and desert tropical and sub-tropical zones. In the Sahel its southern border is around the isohyets of 300 to 400 mm; it is essentially a Saharo-Sahelian species; it relays towards the North Faidherbia albida whose pastoral role can compare with it. Multiplication is quite easy and has allowed important plantations in Senegal, Sudan, Israel, North Africa, and India with rainfall of 150 to 300 mm. At Birkaner (Rajasthan) as in Mbidi in Senegal, with rainfall of 200-300 mm, A. tortilis is a very fast growing species compared with other arid-zone species. Leaf and pod nutritive value is excellent:

Crude protein 16% DM (13–19)
Net energy 6.1 MJ (3.6–7.6)
Digestible protein/FU 132 (69–173)
P 0.20 (0.12–0.26)

Acacia seyal is a Sahelo-Sudanian species found between the 400 and 800 mm isohyets; its optimum ecological conditions are alluvial soils of a medium to fine texture between the 500 and 700 mm isohyets. Foliage and pods are palatable to livestock and made available to them through pruning, lopping and pollarding. It is often abundant along tracks and roads (dromophileous species), probably due to the large amounts of seeds deposited in faeces along transhumance routes. Leaves and pods have an excellent fodder value:

Crude protein 18.5% DM (11–29)
Net energy 6.5 MJ (3.9–7.6)
Digestible protein/FU 153 (67–237)
P 0.27 (0.14–0.34)

This species will be the object of a detailed review further on, in the chapter on browse management.

Acacia senegal is a typical Sahelian shrub with optimum ecological conditions occurring on sandy soils and with a mean annual rainfall of 300–500 mm. However it may occur on clayey low-lying areas with vertisols, particularly in the Sudan. Being of economic interest, A. senegal has frequently been studied fairly thoroughly, by Giffard, Depierre, Michou, Ross, Gerakis and Tsangatakis, Seif el Din, Obeid, Poupon. Planting in Sahel environments¹ does not present very difficult technical problems and seems economical where mixed gum and browse utilization is planned (Valenza and Diallo, 1980). Leaves and pods have a fodder value similar to other Acacia browses:

Crude protein 22% DM (13–29)
Net energy 5.8 MJ (4.8–7.6)
Digestible protein/FU 206 (87–305)
P 0.20 (0.10–0.30)

¹Plantation costs with a density of 600 plants/ha in Mbidi (Senegal) -350 mm - were US $300/ha (60.000 CFAF), for an expected gum harvest of US $30/ha/year for the producer.

Faidherbia albida (= Acacia albida)

This species, the classification of which has not been undertaken until recent years (Vassal, 1967), has a number of morphological, ontological and cytological characters which clearly distinguish it from the Acacia and more logically relate it to a monospecific genus of the Ingeae family (Albizzia Enterolobium, Pithecellobium), linking it to the Acaciae family, as A. Chevalier had forecast as early as 1934. It is an essentially Sudanian species, with optimum ecological conditions occurring on deep sandy soils between the 600 and 800 mm isohyets. To the north it extends as far as the Sahara along watercourses. In the Sahelian zone, like the Dum palm-tree (Hyphaene thebaica), it is a phreatophyte with special characteristics. Its ecology is similar in western and southern Africa. It grows as high as 1800-2000 m in the Ethiopian Rift Valley, where it is abundant, in the Blue Nile Valley and also in northern Somalia, and is even found at 2300 m locally on Jebel Mara in Sudan (Wickens, 1969). Botanists have put forward a host of conjectures and theories (Aubreville, Lebrun, Trochain, Ross, Brenan, Wickens, Vassal, Porteres etc.) to explain the abnormal physiology of this curious species, which loses its foliage during the rainy season and keeps it throughout the dry season (though this appears less clearly under equatorial climates with a bimodal rainfall) unlike most, although not all, other deciduous species.

The agro-pastoral systems developed by several African peasant societies based on apple-ring exploitation and millet and sorghum crops, seem to have arisen independently: for example, the Galla and Arussi farmers in the Ethiopian Rift Valley, have developed a park-like landscape similar to that of the Sereres in Senegal. The agro-pastoral system and its advantages in terms of preserving soil fertility have been the object of very detailed research studies in the fields of agrology, pedalogy, microbiology and bioclimatology (Charreau and Vidal, 1965; Charreau and Nicou, 1971; Giffard, 1964, 1972; Jung, 1970; Schoch, 1971; Dancette et Poulain, 1969; Radwanski and Wickens, 1967; Wickens, 1969).

From a pastoral point of view, Faidherbia albida makes excellent browse, as many authors have indicated (Curasson, 1953; Boudet, 1962; 1969; Bartha, 1970; Peyre de Fabregues, 1963, 1967, 1969, etc.). The fruit is marketed in Sahelian and Sudanian countries, for feeding and fattening sheep and prestige animals, and for family milk production. One kilo of dry pods was sold for 25 MF (=12.5 CFAF= 0.07 US $) on Malian markets in 1978 (Mopti, Segou). The nutritive value is as follows:

	Leaves	Pods
Crude protein	15–20%	10 –15% DM
Net energy	6– 8 MJ	5–7 MJ
Digestible protein/FU	100–180	20–80
P	0.20–0.30	0.10–0.20
Digestibility of DM (Dicko-Touré, 1979)	53.03	50.46

Pod production on unpruned adult trees ranges from 50 to 150 kg DM/tree/year. In fact, since trees are nearly always pruned periodically, pod production is much lower, 10-20 kg/ tree/year, with a similar amount for leaves.

Leucaena leucocephala, a tropical Mimosoideae from Central America, is still seldom utilized in West Africa though it offers very promising possibilities for the Sudanian and Guinean zones, due to its exceptionally good forage quality (equal to or higher than alfalfa and its high productivity in areas with all the necessary ecological requirement (R > 800 mm; rainy season > 5 months; minimum temperature of coldest month > 12°C; altitude < 1600 m).

Intensive forage plantations have been introduced for meal production from Leucaena leaves whose dietetic traits are very similar to those of alfalfa-leaf meal though slightly higher. Plantations of this kind have been established in Malawi (see the contributions of Beale and Savory to this symposium). They are being introduced in many African countries. The utilization of Leucaena as forage offers excellent prospects in the African humid tropics, in particular in the southern Sudanian and Guineo-Congolese zones, as stated by Audru (1980).

The question of toxicity for ruminants owing to the mimosine content is a fictional problem since varieties with a low mimosine content are used (Cunningham) and since if Leucaena forage is utilized in a rational basis, i.e. as a protein supplement, toxicity risks are almost nil for varieties with a low mimosine content, such as cultivars Salvador and Peru, or where Leucaena represents less than 30% of the daily intake (in DM), more than enough to ensure a well-balanced diet with roughage such as crop by-products or rangeland straw.

The nutritive value of leaves and meal is as follows:
Crude protein 25% DM (12–31)
Net energy 7.2 MJ (6.8 –7.7)
Digestible protein/FU 184 (150–275)
a carotene 0.053°/a (536 mg/kg DM)
Lysine 50 mg/g/C. Protein
Apparent digestibility of O.M. 60% (50–70)

Prosopis juliflora (P. dulcis)

This species is often confused with three others, P. chilensis, P. glandulosa and P. velutina, since the classification and taxonomy of this group were a complete muddle until Burkart recently revised them (1976). The four species (sometimes considered as subspecies or varieties) include spiny and spineless forms. P. glandulosa from Mexico and P. velutina from the southern USA are considered dangerous weeds which invade pastures, and the literature on the various means of keeping them under control are plentiful, since it once invaded over 30 millions/ha of rangeland from Texas to Southern California, costing several hundred million dollars to eradicate.

It appears that most of the plantations established in West Africa and Sudan actually consist of P. juliflora, a Central American and Caribbean native species. It adapts quite well to the Sudanian zone but needs either a shallow water table or a coastal or subcoastal climate (Cap-Verdian climate) or both, before it will thrive in a Sahelian zone. Such is the case, for example, in the lower Senegal Valley, the Cap Verde peninsula, the area around Nouakchott, or the Cap Verde Islands, where it thrives with rainfall reaching 150-200 mm. Hence there is unfortunately no chance that this species will grow as a weed in the Sahelian zone as it does in other arid zones (some areas in Rajasthan (Jodhpur), where rainfall reaches 300–500 mm).

Leaves are moderately palatable to animals, but goats and camels are rather fond of them. Pods have a good forage value, especially as regards energy, and are consumed by all animals and occasionally by man, on account of their high sugar content.

The nutritive value is as follows:

	Leaves	Fruit
Crude protein	19% DM (13–23)	12% DM (9–14)
Net energy	5.8 MJ (3.5–6.4)	6.0 MJ (5.2–7.1)
P	0.16 (0.13–0.21)	0.16 (0.13–0.20)

Meliaceae

Khaya senegalensis is a beautiful tree common throughout the Sudanian zone of which it is typical. It has often been planted as an ornamental or avenue tree. It produces excellent industrial timber (Senegalese mahogany). In many Sudanian zones, branches are pruned or pollarded to be fed to livestock in the dry season: Mali, Upper-Volta, Ivory Coast and Nigeria, among others. Leaf-bearing twigs are sold in towns for feeding to fattening sheep and dairy cattle for example in Bamako.

The nutritive value of young leaves is good:
Crude protein 15% DM
Net energy 6.2 MJ kg DM
Digestible protein/FU 125
P 0.16

Moraceae

Ficus gnaphalocarpa. Some fig trees in the Sudanian and Guinean zones are consumed by livestock (leaves and fruit). The main species is G. gnaphalocarpa. It is mentioned by many authors, and was experimentally studied by Rose-Innes in Ghana. The nutritive value (leaves) is as follows:

Crude protein 9.0% DM
Net energy 7.3 MJ kg DM
P 0.14
Digestible protein/FU 45

Another Guinean Moraceae (Antiaris africana) has a similar forage value (Rose-Innes, 1966) with a dry matter digestibility ratio of 64% and 77% for crude protein and a daily intake of 2.27 kg DM per 100 kg liveweight for dwarf shorthorn breeds of West Africa (Mabey and Rose-Innes, 1966).

Rhamnaceae

Ziziphus mauritania is a typically Sahelian tree 10–15 m in height. In the natural state it has a large dense foliage crown, although it will rarely be seen in this form except in protected areas. Usually it is a multistemmed tree 1–3 m high on high undershrub, growing in somewhat intricate bushes owing to its over-utilization. Stumps put out thriving shoots and it successfully withstands the repeated crippling attacks made by shepherds and goats.

Leaves and fruit are consumed by camels and small ruminants, and to a lesser extent by cattle and monogastric animals. The fruit is consumed by camels, small ruminants and occasionally by man. The nutritive value (leaves) is as follows:

Crude protein 15.5% D (11.1–26.4)
Net energy 6.6 MJ (5.5–7.3)
Digestible protein/FU 109 (67–221)
P 0.16 (0.13–0.21)
Digestibility of DM (leaves) 51.24% (Dicko-Touré, 1979)

Rubiaceae

Feretia apodanthera (= F. canthioides)

This bush-like shrub of Sahaelian and Sudanian zones is located in the Sahel, in low-lying areas where the soil is temporarily waterlogged during the rainy season, on pond fringes, etc. Its foliage and young twigs are palatable to livestock. The nutritive value is as follows:

Crude protein 11% DM (7-14)

Net energy 6.5 M 5 kg DM (4.6-7.8) Digestible protein/FU 87 (41-137)

P 0.14 (0.07-0.20)

Gardenia ternifolia, G. erubescens, G. aqualla

These three Sudanian and Guineo-Sudanian shrubs are palatable to livestock but have only an average to poor feeding value:

Crude protein 7.5% DM (5-12) 
Net energy 6.1 MJ (4.6-6.7)
Digestible protein/FU 45 (14-90) 
P 0.15 (0.05-0.35)

Salvadoraceae

Salvadora persica is a Saharan or sub-Saharan shrub or undershrub, more or less crassulaceous phreatophyte and halophyte. It is rarely found in conditions where rainfall is higher than 200 mm except on really saline soils in the Sahel. Its range extends into East Africa and the Middle East. A variant species, S. oleoides, can be found under rather similar conditions in Rajasthan. Thanks to its high mineral content, S. persica represents a "salt-cure" in its own right. The nutritive value of leaves is as follows:

Crude protein 13% DM (10–17)
Net energy 4.8 MJ kg DM (3.2–-6.0)
Digestible protein/FU 137 (108–-193) 
P 0.10 (0.08–-0.13)

Silica-free minerals 29% DM (20–-36)

Tiliaceae

The Sahelian and Sudanian forage Tiliaceae, belong to the Grewia genus widely spread in the arid and semi-arid tropical zones of Africa. The main species is indisputably G. bicolor, also well represented in East Africa. G. tenax extends into the Sahara but is of limited interest owing to its very short leafy phenophase. G. bicolor is common between the isohyets 200 and 800 mm, especially in low-lying areas, or in association with termitaria. Its foliage is palatable to all herbivores in the dry season. The nutritive value is average to good:

Crude protein 11% DM (4–20)
Net energy 6.2 MJ kg DM (5.6–6.8) Digestible protein/FU 77 (25–154)
P 0.14% DM (0.09–0.20)
D.M. Digestibility (G. carpinifolia) 69.5%a C.P. Dig. 77.8%.

^a(Mabey and Rose-Innes, 1965)

Other species are very palatable but rather rare: G. villosa or G. carpinifolia. The latter has been studied by Rose-Innes and Mabey (1966) with the following findings:

Digestibility 69.5% DM
Crude protein 18.0
Daily intake/DM 1.82% live weight
Net energy 6.6. MJ kg DM
Digestible protein/FU 134
P 0.10%

Ulmaceae

Celtis integrifolia is a Sudanian tree that can also be found in the Sahel in humid low-lying areas up to the 400 mm isohyet; it spreads as far as East Africa. Like its Mediterranean congener, C. australis, its foliage represents a food forage with a high mineral content, palatable to all animals during the dry season, in West and East Africa. The nutritive value is as follows:

Crude protein 11% DM
Mineral 25% DM (with 50% Si02)
P 0.20 DM

Verbenaceae

In the southern-Sudanian and Guinean zones, some Vitex species, V. madiensis, V. doniana and V. cuneata, are palatable to cattle in the dry season (Piot, 1969, 1970) and have a fair forage value:

Crude protein 12% DM
Net energy 5.4 MJ kg DM Digestible protein/FU 98
P 0.23% DM

Zygophyllaceae

Balanites aegyptiaca is perhaps the most typical tree or shrub in the Sahel, sometimes classified in the Simaroubaceae, Zygophyllaceae or Balanitaceae families. It extends throughout the driest environments of the northern Sudanian zone and as far as the centre of the Sahara along the main wadi bottoms. In the Sahel, it settles on all soils and under any topographical conditions. Its multiplication appears to be related to man's activities: it is always more plentiful around past or present human settlements. The leaves, which fall as early as January in the Sahel and the chlorophyllous twigs are palatable to both domesticated and wild herbivores. The fruit is also palatable, the kernels containing 40% of edible oil which, once extracted, yields cakes similar to groudnut cakes with 50% protein and 36% glucose. The fruit and bark contain a hydrosoluble ichtyotoxic saponoside toxicant for Bullinus and Planorbis Gasteropods, bilharzia vectors (Wickens, 1980). Nutritive value (leaves and twigs):

Crude protein 15% DM (6–24)
Net energy 6.1 MJ kg DM (5.5–6)
Digestible protein/ FU 100(20–236)
P0.11 (0.03–0.20)

4.2 Secondary species

Secondary browse species are very plentiful in the Sahelian and Sudanian zones. It will be sufficient here to merely give a list of them, and the reader is asked to refer to Toutain's study (1980) for the Sudanian zone and to the present author's two reports of 1979 for the Sahelian zone, the chemical components and the feeding value respectively.

Anacardiaceae

Lannea acida-L. humilis, Sclerocarya birrea are Sudanian and Sahelo-Sudanian species consumed by livestock to a fair degree.

Mangifera indica (mango-tree) is a southern Sudanian and Guinean species whose leaves and fruit are eaten by livestock (Toutain, 1980; Dicko-Touré, 1978).

Araliaceae

Cussonia kirkii (= C. barteri) is a Sudanian species locally utilized by livestock).

Asclepiadaceae

Laptadenia pyrotechnica is a Saharan and Sahelo-Saharan species, while L. hastata is Sahelo-Sudanian. The former is consumed by camels and the latter by donkeys and to a lesser extent by goats.

Bignoniaceae

Stereospermum kunthianum is a Sudanian or Southern Sahelian small tree or shrub sometimes consumed in both West and East Africa, though of a poor forage value.

Bombacaceae

This family comprises three species browsed to a greater or lesser degree: the baobab Adansonia digitata, the false kapok tree Bombax costatum, and the silk cotton-tree Ceiba pentandra. The baobab is a southern Sahelian and northern Sudanian species with an ecologic optimum between the 500 and 1000 mm isohyets. See Wickens (1979) for its multiple utilization. The leaves are moderately consumed by livestock but the fruit pulp which is very rich in vitamin C, is palatable to many animals among which small ruminants, monkeys and man. Fallen dry leaves are sometimes eaten by livestock. Green leaves are used in cooking.

The false kapok tree is an essentially Sudanian species and its fallen flowers are readily consumed, though of a poor feeding value.

The silk cotton-tree, a Guineo-Sudanian species, is virtually untouched by livestock.

Capparidacese

Boscia senegalensis, though virtually unpalatable, is very rich in protein (30–35%DM). Research should be carried out on the utilization of this Sahelian undershrub (palatability, utilization of dry ground leaves, cultivation etc.).

Celastraceae

Maytenus senegalensis (= Gymnosporia senegalensis) a Sahelo-Sudanian shrub, is sometimes substantially browsed though of a poor nutritive value. The same is true for other species of a similar genus in East Africa.

Chailletiaceae

Dichapetalum guineneense, studied by Rose-Innes in the subhumid zone in Ghana, has an indisputable forage value.

Combretaceae

A certain number of Combretaceae, mainly Sudanian, have some forage value especially:

Anogeissus leicarpus, Guiera senegalensis, Combretum geitonophyllum, Terrninalia avicennoides, Terminalia macroptera.Guiera, very abundant on sandy soil fallows between the 500 and 800 mm isohyets, is sometimes considered as a forage species (particularly in Senegal) and sometimes found unpalatable (Nigeria). There may be populations with different levels of palatability.

Ebenaceae

Diospyros mespiliformis is a Sudanian species invading humid low-lying areas in the Sahel.

Euphorbiaceae

Hymenocarida acida, a Sudanian shrub, is found in the Sahel in low lying areas. Its folliage, which has a good feed value, is eaten by livestock. Securinega virosa, a Sudanian shrub, consumed to some degree.

Graminaceae

Oxytenanthera abyssinica, a bamboo whose young leaves and twigs are palatable, has a poor forage value.

Leguminoseae

Among the Cesalpinioideae, Piliostigma reticulata and P. thonningii may be mentioned, the former Sahelo-Soudanian and the latter Sudanian. The pods are consumed in both cases. Cassia sieberfana. The pods of this otherwise unpalatable shrub are consumed by ruminants. Isoberlinia doka, a Guineo-Sudanian species, is sometimes considered as a good browse, though it has not yet been the object of more detailed study, as far as the present author is aware.

Mimosoideae

The species in this sub-family play an important part in the Sahelian and Sudanian zones. Beside the main species already mentioned, some others can be noted:

A. Sahelian zone: Acacia nilotica adansoni, Acacia tomentosa, Acacia ehrenbergiana, Acacia mellifera, Acacia nubica, Acacia laeta, Dichostachys cinerea, B. Sudanian zone: Albizzia amara, Albizzia chevallieri, Albizzia zygia, Acacia ataxacantha, Acacia macrostachya, Acacia dudgeoni, Acacia siberiana, Prosopis africana.

Other species have been introduced, among which the following: in the Sahelian zone (Le Houérou, 1980; Lepape, 1980): Prosopis julijflora² Parkinsonia aculeata (Cesalpinioidease), Prosopis chilensis; and in the Sudanian zone (Boudet et Toutain, 1980; Toutain, 1980; Le Houérou, 1980): Pithecellobium dulce, Leucaena leucocephala and Pithecellobium saman.

²Despite Burkart's recent monograph (1976), the taxonomy of this group is still very confused.

Beside these species which look highly advantageous, the recent and promising Senegalese introductions of phyllodinous Australian Acacias may be mentioned (Hamel, 1980): A. linarioides, A. bivenosa, A. tumida, A. pyrifolia, A. plectocarpa, A. holosericea, A. salicina, A. coriacea, A. sclerosperma.

Further confirmation concerning their adaptation to the Sahelian zone, their palatability and their nutritive value is still required but preliminary results have justifiably given rise to optimism concerning both forage and firewood production, as well as erosion control or utilization as windbreaks (Hamel, ibid).

Papilionoideae (= Fabacoideae)

Dalbergia melanoxylon, a Sudanian species, is found in the Sahel in more humid places; it suffered much from droughts between 1970 and 1974 (Poupon, 1979).

Dalbergia sissoo, an Indian species, gives one of the best performances for Sahelo-Sudanian afforestation. It is known as a good browse in its native country.

Among the Papilionoideae a number of Sahelian chamaephytes should be mentioned on account of the forage value attributed to them by some authors. Further research should be carried out on these species:
Indigofera arenaria, I. bracteola, I leprieurei, I prieureana, I spinosa, I oblongifolia, Crotalaria podocarpa, C. arenaria, C. atrorubens, C. barkae, C. microcarpa, C. macrocalyx, Tephrosia purpurea, I quartiniana, I linearis, I bracteolata, I obcordata, Aeschynomene crassicaulis, A. indica, A pfundii, Stylosanthes scabra (introduced), S. viscosa (introduced), S. subserisea (introduced), Crotalaria thebaica, C. Saharae, C. aevptiaca, C. vialattei, Sesbania leptocarpa, S. pachycharpa, S. sesban, Psoralesa plicata, Cajanus, cajan (introduced), Stylosanthes hamata verano, S. guyanensis, S. erecta, Stylosanthes fruticosa, Desmanthus virgatus, Rhynchosia minima, R. memnonia.

All these species have been indicated as good fodder in various studies; preliminary surveys followed by systematic experimentations should be carried out to determine the agronomic potential of these species. This opinion is reinforced by the fact that in terms of both the number of species present and their abundance the arid and semi-arid zones are poor in perennial forage legumes. Moreover, the research carried out by CSIRO Australian agronomists on local Mediterranean and tropical South American flora has enabled some perennial forage legumes of the semi-arid zones to be selected, although they were formerly considered as weeds. These include:

Stylosanthes hamata, s. viscosa, S. subsricea, S. scabra, S. fruticosa, S. erecta, and of course, Leucaena leucocephala, of all which plants may also be of value in the southern Sahelian and Sudanian zones, especially for improving fallow land. Australian achievements in this area, using Mediterranean native (Medicago, Trifolium) or tropical (Stylosanthes, Macroptylium, Macrotyloma, Desmodium, Centrosema, etc.) species should not be omitted, since they started a real "green revolution". Afro-tropical flora have been little explored in this connection and only as regards the East African highlands.

Rhamnaceae

The Rhamnaceae offer a list of potential valuable species, but these are of no importance for the moment because they are relatively rare:

Ziziphus jujuba, Z. pseud ojujuba, Z. abyssinica, Z. mucronata, Z. spina-christi. It should be mentioned that a jujube from northeast Brazil, Z. joazeiro, is locally considered to be one of the best browses available.

Rubiaceae

Mytragyna inermis is a shrub associated with the Sudano-Guinean zone but which is found in the Sahel in humid places. Leaves and young twigs are palatable to small ruminants. Forage value is very good.

Sapotaceae

Butyrospermum paradoxum (=Vitellaria paradoxa). Young shoots and dry leaves of the shea butter tree, a typically Sudanian tree, are consumed and represent a good forage according to Toutain (1980).

Sterculiaceae

Sterculia setigera; the consumption of young leaves and fallen dry leaves of this small Sahelo-Sudanian tree has sometimes been noticed. The value of this forage is poor.

Tiliaceae

Many Tiliaceae, particularly Grewia villosa, G. tenax, G. flavescens, G. mollis, contribute to a fairly large extent to livestock feeds, although they are less important than G. bicolor. G. villosa, common in East Africa, seems to be more palatable there than in the Sahelian and Sudanian zones, where it is less common.

4.3 Common woody species, not usually consumed

Adenium obesum, Annona senegalensis, Bridelia ferruginea, Calotrpi procera, Cissus spp., Crossopterixfebrifuga, Detarium microcarpum, Diospyros mespiliformis, Erythrina senegalensis, Euphorbia balsamifera, Ficus spp., Pergularia tomentosa, Cocculus pendulus, Combretum glutinosum, C. micranthum, C. molle, C. nigricans, Securinega virosa, Sterculia setigera, Tapinanthus spp., Pitex spp., Ximenia americana.

5. Forage production of browse species

5.1 Individual production of trees and shrubs

The individual production of trees and shrubs has been the object of detailed and timely studies under the ORSTOM programme at Fété-Olé in the Sahelian zone of Senegal (Poupon, 1976, 1977, 1979; Bille, 1977), and as part of the ILCA programme in the Sahelo-Sudanian zone at Niono in Mali (Cissé and Hiernaux et al,1970,1979; Cissé,1980). Other studies are being carried out in the Sahelian and Sahelo-Sudanian zones in Upper-Volta (Nebout and Toutain, 1978; Grouzis and Sicot, 1980). Several contributions to the present symposium relate these studies (Cissé, Bille, Grouzis and Sicot) so only some of the conclusions arising from them will be formulated here. Correlations between leaf biomass and trunk circumference (or diameter) are satisfactory (0.86<r<0.98). Predictive equations naturally vary from one species to another, and also according to the ecological zones under review. Probably they also vary according to specific populations, so that working out a predictive equation for a given species for the whole Sahelian or Sudanian zone, does not seem to be possible at present. Predictive equations are linear: (log y= a) log x + b) or exponential (y= ax^b) where y= leaf biomass, x = stem circumference and a and b are specific site constants.

A relatively limited number of species has been studied: 
Acacia senegal, Acacia seyal, Acacia tortilis, Adansonia digitata, Balanites aegyptiaca, Boscia senegalensis, Combretum aculeatum, Commiphora africana, Faidherbia albida, Grewia bicolor, Guiera senegalensis, Pterocarpus lucens, Ziziphus mauritiana.

Mean yields show the following figures:

a) Fété-Olé(1971-77)—long-term mean rainfall: 340 mm; rainfall over the period of measurements: 220 mm.Data calculated from figures published by Poupon (1979). N.B. These figures are certainly lower than long-term means, since they were obtained over a period with a very poor rainfall: less than 100 mm for two years (1972-1977) and three years showing a deficit of 40% (1970, 1971, 1973).

Fruit production is also related to the various allometric parameters, similarly to leaf production (trunk circumference, height, crown surface, biovolume etc.)

In the Niono area, Cissé obtained the following figures:

Faidherbia albida unpruned	10.0 kg/tree/year
Faidherbia albida pruned	6.0 "    "    "
Acacia seyal	0.7 "    "     "
Pterocarpus lucens	1.8 "    "    "

At Fété-Olé Poupon gives the following figures (1971–77):

Total sampling area	0.013 kg/tree/year
Commiphora africana	0.090 "     "     "
Balanites aegyptiacea	0.540 "     "     "
Grewia bicolor	0.760 "     "     "
Boseia senegalensis	0.043 "     "     "
Acacia senegal	0.054 "     "     "
Guiera senegalensis	0.011 "     "     "

i.e. 11.9 kg/ha/year for 841 individuals/ha

It should be noted that the figures for pod production given in the literature for Faidherbia albida (Charreau and Vidal, 1965; Giffard, 1971; Radwanski and Wickens, 1967; Wickens, 1969; Le Houérou,1980), and varying from 50 to 150 kg/tree/year were obtained on unpruned tall trees. These figures are not very reliable due to the pinpoint measurements in time and space through which they were obtained. When studying production for a total population and over several years, more modest figures are obtained, of the order of 10–20 kg per tree and per year (Cissé, 1979), for example, in the Segou district (750 mm).

Determining the fruit production of Acacia, especially A. tortilis, A. seyal and A. albida, seems extremely important. Total net production in FU maybe higher with fruit than with leaf or mixed utilization. But as far as the present author is aware, this theory is still to be verified. The implications for optimization of stand management would naturally be enormous. F albida pods were being sold on Malian markets at 25 ME ($ 0.06 US) per kg in 1979, i. e. 32 MF/FU, which makes it a cheap concentrate.

5.2 Production from plant association

Determining this production implies relevant studies such as those mentioned above, as well as a demographic study of the populations, their phytosociological definition and their cartography (for the latter, see Hiernaux's communication to this symposium).

Unfortunately there are few data on the forage production of browse associations in the Sahelian and Sudanian zones. This shortage of information may be explained in several ways: one of the main reasons relates to the difficulties of this subject. It requires long, painstaking and numerous measurements, which are in any case not very accurate. Research carried out over recent years, especially in Senegal (Bills, 1977; Poupon, 1976, 1979), Mali (Cissé, 1978, 1979, 1980), Upper Volta (Nebout and Toutain, ), Ivory Coast (Menaut, 1977) and Cameroon (Piot, 1969), has nevertheless permitted an overall estimation, something which was impossible only five years ago. It should be mentioned that these pinpoint studies have never been extended on a regional basis, except in the case of Hiernaux's work (1980) in the central zone of Mali. Taking these various studies as a basis, a mean estimation for consumable browse can be obtained:

1 kg DM/mm/ha/year (Le Houérou, l979), which is the equivalent of:

150 kg DM/mm/ha/year	in the Saharo-Sahelian zone
300 "    "     "    "    "	in the Sahelian s.s. zone
500 "    "     "    "    "	in the Sahelo-Sudanian zone
700 "    "     "    "    "	in the northern Sudanian zone
1000 "  "     "    "    "	in the southern Sudanian zone

This estimation is slightly inferior to Bille's (1980) and to Hieranaux's (1980) and also to that found for Mediterranean North Africa (1.4 kg DM/ha/mm/year). (Le Houérou 1979; Floret and Le Floch, 1980). This estimate is based on the hypothesis of a utilisation coefficient of 50% for deciduous biomass. Of course this coefficient may vary considerably in terms of vegetation structure, animal species and the management practices of herdsmen (lopping, pruning, pollarding, etc.).

For example at Niono (550 mm), Hieranux has estimated the total deciduous production at 1000 kg/ha/year/DM on average, i.e. 20 kg DM/ha/mm/year, with deviation ranging from 21 kg/ha/year for open associations of Combretum ghazalense and Sclerocarrya birrea on sands, to 3536 kg/ha/year for virtually enclosed associations of Pterocarpus lucens on clay.

If daily requirements of 1 g crude protein per kg of liveweight and per day (maintenance, trekking, growth) are accepted, a figure of 275j250g=68.7 kg of CP per TLU for the length of the dry season is obtained. The mean CP content is 125 g per kg DM for the whole of West African browse (Le Houérou, 1980), so 1 TLU should consume 2 kg of browse per day, i.e.= 32% of its daily intake, assuming

that the balance of the diet contains no digestible protein whatsoever, which is not always true. Each TLU should thus consume 2752=550 kg of browse for 1168 kg of grass during the dry season. In the well-balanced (non-degraded) pastoral ecosystems of the Sahelo-Sudanian area, consumable browse biomass represents nearly half of grass biomass (Boudet, 1970; Hieranux, 1980)

The figures have been confirmed experimentally in Senegal (Blancou et al, 1978), where the mean browse content of fistulated cattle is 25% (5–45) during the dry season.

This figure fits perfectly with the estimate of 32% given above, the fact that the herbaceous part of the total intake may not be entirely lacking in protein being taken into account.

The same argument can be applied for phosphorus and carotene. Dry season straws contain an average of 0.05% P, whereas 0.12% is required (Le Houérou, 1979