H.N. Le Houérou
Principal Scientist, International Livestock Centre for Africa
2.1 Arid zone with a cold winter climate (central and southwestern Asia):
2.2 Arid zones with a temperate climate:
2.3 Semi-arid Mediterranean areas (400 < P < 600 mm):
2.4 Arid Mediterranean areas (100 < P < 400 mm):
2.5 Semi-arid and arid tropical areas:
2.6 Sub-humid and humid tropical areas:
9. Enemies, pests and parasites
10. Exploration, evaluation and utilization of genetic resources
11. Gaps in knowledge and research priorities
The precise extent of areas covered by plantations of ligneous species suitable for browse throughout the world is not known, but it is certain that they amount to millions of hectares.
Amongst the most frequently cultivated species the following spineless cacti should be mentioned: Opuntia ficus indica f. inermis, O. inermis, O. robusta, O. fuscicaulis, Nopalea cochenillifera.
Spineless cacti plantations suitable for browse cover over 300,000 ha in NE Brazil, probably nearly 200,000 ha. in N. Africa, 100,000 ha in Sicily and considerable areas in S. Africa, S.W. Madagascar, Mexico and Texas. The honey locust tree, Gleditschia triacanthos, and the false acacia, Robinia pseudoacacia, are planted in arid areas with a temperate climate and play a by no means inconsiderable role in browse supply.
The carob tree in the Mediterranean area should also be noted, as well as the mulberry tree in various tropical, subtropical, Mediterranean and sub-Mediterranean-climates, while Leucaena leucocephala is expanding fast in humid tropical areas, as also are the phyllodineous Australian acacias in various countries, especially around the Mediterranean, Atriplex species in several arid Mediterranean, north and south American areas, and the saaul or Haloxylon species and Calligonum species in arid areas of Asia. Prosopis and Parkinsonia spp. in south America (Chile), India and some of the hotter arid zones of the world, and finally the African acacias, especially Faidherbia albida, A. senegal, A. tortilis, A. nilotica, as well as other species, including Mediterranean and tropical legumes, have an undoubted value in terms of animal feed, especially for marginal agricultural areas in the arid or montane zones. These species include Medicago arborea, Coronilla glauca, Hedysarum argentatum, Cassia sturtii, Pithecellobium dulce, P. saman ( = Samanea saman), Tipuana speciosa ( = Macarium tipu = Tipuana tipu). However, these species are not yet planted over large areas.
Finally, the olive tree should not be omitted. It covers approximately 8 million ha in the Mediterranean basin (of which 3 million lie in North Africa), S. America and California, while its branches and leaves after pruning are distributed to livestock, at least in Mediterranean areas.
The same also applies to American vines such as Vitis rupestris, V. berlandieri, V. riparia and their hybrids, which serve as rootstocks for cultivated vines (V. vitifera) since the phylloxera crises of 1850–1880. Their prostrate habit, their good ground cover and palatability make them ideal species for combating erosion in montane livestock production areas.
The choice of species depends primarily on the ecological and specially the bio-climatic conditions of the areas to be planted. The conditions can be summarized in rough terms as follows:
Haloxylon persicum, Haloxylon aphyllum, Calligonum polygonoides, Calligonum spp. (C. arborescens, C. caput-medusae, C. pellucidum, C. setosum, C. clatum and C. eriopodum), Salsola paletskiana, Salsola ritcheri.
Robinia pseudoacacia, Eleagnus angustifolia.
Acacia cyanophylla, Ceratonia siliqua, Gleiditschia triacanthos, Medicago arborea, Coronilla glauca, Morus alba, Vitis spp. Opuntia ficus indica, Eleagnus angustifolia.
Acacia cyanophylla, Acacia salicina, Acacia ligulata, Acacia victoriae, Acacia aneura, Opuntia ficus indica, Atriplex nummularia, Calligonum comosum, Calligonum azel, Calligonum arich, Periploca laevigata, Chenopodium auricomum, Artemisia herba alba, Prosopis juliflora, Atriplex canescens, A. halimus, A. lentiformis, A. semibaccata, A. glauca, A. repanda, A. atacamensis, Prosopis chilensis, Parkinsonia aculeata, Maireana brevifolia, M. sedifolia, M. pyramidata, M. astrotricha, Cassia nemophila var. coriacea (=C. sturtii).
Acacia senegal, Faidherbia albida, Acacia nilotica subsp. indica, Acacia tortilis subsp. tortilis subsp. raddiana, subsp. spirocarpa subsp. heteracantha, Parkinsonia aculeata, Desmanthus virgatus, a. bivenosa, A. linaroides, A. tumida, Combretum aculeatum, Bauhinia rufescens, Ziziphus mauritiana, Zizphus mucronata, Z. spina-Christi, Z. joazeiro, Nopalea cochenillifera.
Leucaena leucocephla (= L. glauca), Samanea saman (= Pithecellobium saman), Pithocellobium dulce, Morus alba.
Morus alba, Opuntia ficus indica, Nopalea cochenillifera, Atriplex nummularia, Atriplex halimus, Atriplex canescens, Ormocarpum trichocarpum, Canthium bogoensis.
These broad categories should be subdivided on account of the wide diversity of local bio-climate in terms not only of temperature but also of rainfall and humidity. The latter in particular is likely to play a very important part, and some examples are given in what follows.
Dry tropical regions are not all equal in terms of ecology, especially as a function of the rainfall regime, which can be mono-modal or bimodal and of air humidity, which may be higher or lower. Cacti and Atriplex species, for example, cannot be established in the Sahel zone, even with rainfall reaching 400–600 mm. On the other hand, they are widespread in the Cape Verde peninsula, in the Cape Verde islands, in East Africa, as well as in NE Brazil, with rainfalls lower than 400 mm. However, in Cape Verde, East Africa and NE Brazil average daily air humidity is never lower than 40%, whereas it is lower than this level for over 6 months each year in the Sahel.
Another example may be taken from the Mediterranean zone. Cacti do not become established over 1200 m in altitude, or more precisely, wherever average minimum temperatures in January are lower than 1°C. On the other hand, the mulberry and the honey-locust and the Russian olive withstand very low winter temperatures. Phyllodineous Australian acacias are sensitive to frost, while Atriplex species are not, although the resistance to drought is comparable.
Obviously, the nature of the soil also plays an important part; Atriplex varieties with the exception of A. canescens require loamy to clayey soils with an alkaline reaction, while phyllodineous Acacias need sandy soils or at least well drained soils, as also do cacti; the oleaster is much better at withstanding clay soils and temporary water logging than the cultivated olive. The white saxaul (Haloxylon persicum) requires sandy or even duny conditions while the black variety (H. aphyllum) prefers loamy soils with some salt content, etc. Faidherbia albida needs deep well-drained soils, preferably sandy (e.g. dior soils), while A. senegal, although preferring sandy conditions, can, if need be, adapt to vertisols. A. nilotica and A. seyal, on the other hand, behave entirely differently, the former preferring clayey riverbank conditions while the latter is more inclined to open depressions where clay is present. Many further examples could be given.
The choice of species also depends on the production system envisaged, for example: pure pastoralism, transhumance, sedentary systems, agropastoral systems, arable farming, extensive or intensive systems. The type of system in turn depends on socio-economic factors such as the abundance or scarcity of labour, its quality and its cost. Generally speaking plantations of browse trees and shrubs are better adapted to sedentary semi-intensive systems where labour is plentiful, relatively inexpensive and where the level of management of range and herds can be assessed as medium to good involving fencing, control of stocking rates and grazing rotation.
However, in some cases where animal products of local origin reach very high prices, which are of course artificial, such as some of the oil producing countries, it is possible to establish plantations at very high establishment and utilization costs.
Establishment techniques depend on the species under consideration and on local ecological conditions. The main methods used are:
a) direct drilling;b) planting out of young plants raised in the nursery;
c) planting rootstocks;
d) planting out cuttings, before or after the roots have been set;
d) grafting.
Direct drilling is used only for a small number of species, generally those with low height and a high rate of germination with rapid development from the seedling stage. This is the case for: Atriplex semibaccata, Atriplex glauca, Atriplex canescens (seeds removed from their wings), Haloxylon persicum, Haloxylon aphyllum, Artemisia herba alba.
Soil preparation generally takes the form of contoured furrows with a greater or lesser amount of space between them so as to encourage rainwater penetration to the roots of the young plants.
Some species require preparatory treatment, amongst which Atriplex canescens for which the seed wings are eliminated by hammer mill so as both to remove the inhibition caused by sodium chloride and to allow mechanized seed drilling (Springfield, 1967). Direct mechanized drilling was also used by Orev (1972) in Israel and Malcolm et al (1980), (included in the proceedings of this symposium) in Australia. The latter developed a niche-seeder for the direct mechanized drilling of Atriplex and Maireana in western Australia; the trials carried out with this experimental implement are the subject of one of the papers presented at this symposium.
Direct drilling of Haloxylon persicum has been successfully carried out in Iran over relatively large areas and at very low rainfall (80–150 mm) in the Kerman region for example (Le Houérou, 1975).
The advantage of direct drilling is obviously its low cost price.
However, planting out young plants raised in the nursery, although much more expensive, is often preferred, especially in arid areas, since the chances of success are far higher for the reason that competition between the trees and shrubs planted can be more easily reduced or eliminated and that planting densities are low, so that it is possible to provide one or more watering which will help the young plants to recover. The best technique is to concentrate runoff waters on the beds to be planted several months before planting out, so as to ensure that the minimum necessary reserves of water are in the soil. This is best achieved by means of banks with gently sloping sides or by means of blind ditches, etc.
The method for producing young plants in the nursery is the same as used in all forestry nurseries. The young plants should be about 75 to 100 days old when they are transplanted: they should not exceed 20 to 25 cm in height nor have a diameter of over 5 mm at the neck. In the arid zone it is recommended that the resistance of nursery plants should be strengthened by low and infrequent irrigation at least a month before planting out. It is also recommended that the above-ground part of the plant should be cut back to 20 cm, and where appropriate, to trim the roots. The best length for the polyethylene wrappers is 25 cm and their diameter should be 7 cm. The containers are filled with a mixture consisting of one-third sand, one-third loam and one-third dried sheep dung, with 1 kg/m3 of simple super phosphate. The nurseries should be properly sheltered from the wind, a precaution which is too often ignored. Light shading until 10 to 15 days after emergence is often helpful but rarely necessary for arid zone species. Seed scarification before planting is often necessary in order to prevent inhibitions to germination caused by seed coats, especially for Acacia and Prosopis species. This can be carried out mechanically by using scarifiers or by soaking the seeds in boiling water, the proportion in terms of volume being 25 to 50% seeds and 50 to 75% water.
Many species are suitable for propagation by cuttings from the stem or roots, from lignified plant material, from root stalks or from young branches. However, this method, owing to its sometimes high cost, is often reserved for research work or for the initial propagation of ecotypes, populations or cultivars having particular qualities. It is also used in setting up orchards using seeds of dioecious species such as Atriplex nummularia so as to obtain the ideal minimal proportion of males. Propagation by cutting can be practiced in the nursery or out in the field. In the latter case, rooted cuttings may or may not be used. In many cases it will be advantageous to use an ancient horticultural practice (which lay behind the discovery of phytohormones), namely puddling in fresh cow pats or, even better, utilization of synthesizing rhizogenic hormones (Indol Butyric Acid or IBA) (Van Epps and McKell, 1978). An exception to the above is the cactus, for which the usual propagation method is by cuttings. However, it can also be grafted, especially for research purposes or to accelerate propagation of rare or unique varieties or strains.
Propagation by means of branch tendrils is of course the usual method for propagating vines, while rootstocks are one of the most frequently used methods for olive trees.
Preparing the soil for direct drilling depends on current agricultural techniques, consisting of establishing an appropriate seed bed. For trees and shrubs, planting out can be carried out using furrows or holes preferably along contoured banks with a ploughed strip maintained each side of the rows so as to reduce competition from spontaneous vegetation during the early stages of establishment. Competition is often a critical factor in the success or failure of a plantation, especially in the arid zone. With soils having indurated horizons such as lime-crusts or encrustation, iron hardpan and granular (pisolithic) horizons, it is often necessary to carry out ripping or sub-soiling in order to break up the hard layer and help water and root penetration. Sub-soiling can be contoured, following the intended lines of plantation above and below the banks. It is best to carry out sub-soiling one year before planting so as to ensure adequate reserves of water in the soil at the time of planting.
Plant spacing and density depend on the species under consideration, on the development expected and the management and utilization methods planned.
Plantations of Faidherbia albida in millet fields (Pennisetum tiphoideum) sorghum fields (Sorghum sudanense) or groundnut fields (Arachis hypogaea) should use a density of 50 trees to the hectare in rows of 10 × 20 m, for example, thereby avoiding the risk of obstructing mechanized or tractor cultivation. Olive plantations in the North African arid zone use a spacing of 20 × 20 to 25 × 25 m (17 to 25 trees per hectare). Prosopis is planted using spacing varying from 7 × 7 to 20 × 20 m (25 to 200 trees per hectare) according to local conditions, especially depending on the presence or absence of groundwater. Shrubs such as Medicago arborea, Coronilla glauca, Atriplex nummularia, A. halimus, A. lentiformis, A. canescens are planted at densities of 500 to 5000 stocks per hectare depending on environmental aridity, the nature of the soil and the management method (the rate is usually 1000 to 2000 stocks per hectare). In general terms and for a given species, wide spacing encourages fruit production (e.g. Ceratonia, Prosopis, Faidherbia, Gleiditschia), while higher densities encourage the production of leaf biomass per unit area.
In some cases the utilization method imposes a certain spacing: thus in the case of browse cacti to be used in a cut-and-carry system it is necessary to provide room between the rows for the means of transport and harvesting to be used (cart, towing by tractor, lorry, etc), leading in practice to a spacing of 5 to 7 m between the rows, although higher densities would provide greater production. If on the other hand utilization is to take place by animal browsing, higher densities are desirable. But here again it is necessary to leave sufficient space to allow the animals to pass through. Of course there will be a difference according to whether cattle or small ruminants are involved.
Light basic NPK fertilization of 25 to 50 kg per ha restricted to the rows alone provides a spurt to early growth and often enables one or more years to be gained for utilization. However, potassium is quite often superfluous. Some species, such as cacti, show spectacular response to nitrogen fertilizers, which also appreciably increase the nitrogenous content of forage (Monjauze and Le Houérou, 1965). Tunisian peasants producing cactus fruits for market apply about 10 t of sheep dung every 2 to 4 years to their plantation, thereby considerably increasing yields and shortening the waiting time before the first fruit crop is harvested.
Watering immediately after planting out is always beneficial (it makes the soil round the young plants more compact) and is often necessary in arid zones. Watering on two or three subsequent occasions may be necessary, depending on local and seasonal conditions. In some cases in the arid zone starting irrigation, followed by one or two irrigations per annum during the growing season, considerably increases yields, for example for Atriplex, Cacti and Prosopis spp. (Franclet and Le Houérou, 1971; De Kock, 1980; Felker et al, 1980).
For the purpose water which cannot be used in ordinary agriculture because it has too high a salt content can be used, especially on Atriplex varieties (Franclet and Le Houérou, 1971, p. 34).
During the first few years it is always a good idea to reduce or eliminate competition from weeds by ploughing a strip 1 by 2 m wide on each side of the planted rows. This practice allows better establishment in terms of survival percentages and more rapid growth, resulting in earlier utilization which usually compensates more than adequately for the costs (less replanting needed and gains in production of one or more years).
A number of tree species which start with a bushy habit, such as Faidherbia albida, Prosopis, Olea europaea and Ceratonia, require corrective pruning and complete protection from browsing in order to become strong enough to survive independently and develop a trunk.
Other species, on the other hand, need to be cut back so as to remain within reach of the animals (Leucaena, Atriplex nummularia, A. canescens, Medicago arborea and Coronilla glauca). Others with a tendency towards intergrowth need periodic pruning to allow the animals access to the centre of the bush (A. halimus and A. lentiformis).
In most cases it is necessary to enclose plantations so as to avoid damage caused by uncontrolled grazing by livestock and even wild animals. It is often an advantage to use live hedges for the fencing material since they provide better defence, using species such as various spiny cacti (O. dillenii, O. phaeacantha, O. amyclaea, O. rastrera, O. streptacantha, and O. megacantha) or alternatively, Acacia horrida, Aberia caffra, Prosopis cineraria, P. glandulosa, P. velutina, P. juliflora, P. chilensis, Acacia nilotica, A. tortilis, A. caven, A. farnesiana and Acacia seyal. When established in double or triple rows these species rapidly become impenetrable barriers protecting the plantations. Spineless varieties and/or cactoid Euphorbiaceae with rapid development are also used in Africa, such as Euphorbia abyssinica, E. candelabrum, E. tirucalli and E. balsamifera, etc.
The management of a plantation depends on many factors, amongst which the species, the nature of production (fruit or leaves), the nature of utilization (picking or gathering by man or direct browsing by animals or combined solutions such as trimming, polling and lopping, etc), and of course whether the production system is semi-sedentary, extensive or intensive. Obviously it is impossible to take into account here all the combinations which are possible.
Generally speaking browse species are primarily important in terms of providing a feed reserve during annual bridging periods, for example at the end of the dry season or at the end of the winter, and interannual drought periods.
As a result they must be subjected to varied and methodical utilization. In some cases the fruit (Faidheriba albida, Acacia tortilis, Prosopis juliflora and P. velutina) is gathered dry and is stored and occasionally sold. The pods of F. albida were selling in April 1980 at MF 50 (US$ 0.12) per kg on the Malian market (Swift, 1980, pers. comm.) and 45 FCFA (0.23 US$) per kg in Senegal in 1980 (O. Hamel, in litt.). Similar activity can be noted in Mexico with the fruit of Prosopis velutina (Felker, 1980).
Species such as F. albida are subject to mixed utilization involving fruit, leaves and wood. This is made possible by rotational lopping, where by each tree in turn has one main branch out of three or four chopped every 1 to 3 years, as is the case in West Africa, or else branches are trimmed every 5 to 10 years, as is applied in both the Ethiopian Rift Valley and in West Africa. Most species, Atriplex, Phyllodineous acacia, Leucaena, Medicago arborea and Cacti etc., are browsed directly during periods of difficult feed supply or may even be utilized continuously (Leucaena). Animals should of course be barred from browsing during the growing season for shrubs.
Other species are sometimes subject to mixed utilization by trimming and stall feeding as is the case for spineless cacti of North Africa and for Parkinsonia in the Cape Verde Islands as well as the olive and mulberry tree in the Mediterranean. Alternatively the trimmed plant material may by left on the ground for the livestock to eat.
As far as the present author is aware, the intensity of these practices and the intervals at which they are carried out has not been studied systematically with a view to optimizing management. Generally speaking it can also be claimed that homogenous single species plantations are better than mixed plantations. The different species have different biological and edaphic requirements and react differently to utilization, so that it is very difficult to obtain rational management for each one of them when they are mixed together. Mixed Atriplex/Cacturs plantations, for example, always lead rapidly to the elimination of cactus owing to selective browsing. This does not mean to say that species diversity may not be desirable. Diversification of this kind can easily be obtained by having monospecific plantations which are adjacent within the same management unit (farm, ranch, cooperative, etc.).
Species of moderate palatability, such as Atriplex, are generally utilized twice a year. First utilization takes place in spring when the spontaneous species growing between the Atriplex rows are at their maximum production level. At this time the animals consume only those plants which are still green and palatable. During this season Atriplex species are almost completely ignored. The second utilization takes place at the end of summer and in autumn, when the natural grazing grasses are dried and have only a mediocre feed value. At this time the animals concentrate on the Atriplex rows, and the plants are thus subject to almost complete defoliation (Franclet and Le Houérou, 1971). The species used for direct grazing generally need periodic cutting back, either for the purposes of rejuvenating and revigorating of aging plantations, or else to bring the consumable biomass within reach of the animals (or the two reasons at the same time). This is often the case with certain Atriplex varieties (A. halimus, A. lentiformis and A. breweri), whose tendency towards intergrowth fairly rapidly leads to a situation where a large part of the feed biomass is out of reach of the animals, on the inside of the tufts. It should be noted that some species regenerate poorly if cutting back is carried out too close to the neck. This is the case for Atriplex lentiformis (Forti, pers. comm., 1972). Parkinsonia aculeata became senescent at 15 to 20 years, but regenerates vigorously if cut back (Le Houérou, 1980; Lepape, 1980). Shrubs can be cut back mechanically by a rotary dasher or even with a green fodder chopper-blower.
Coppice growth produces an abundance of very palatable forage. It should be utilized carefully and with moderation so as to avoid exhausting the shrubs and killing them off. In the absence of precise data based on systematic trials, it may be estimated that a forage utilization rate of 60% constitutes a maximum which should not be exceeded at each utilization.
The duration of each utilization by browsing should be as short as possible and should not exceed one week as a general rule, so as to permit normal regeneration. Utilization should be sufficiently intense to avoid wastage and provide a consumption of about 60% of available forage. This is particularly important in plantations of spineless cacti utilized by direct browsing, in which the animals, especially sheep, tend to waste the feed (joints which are started and then abandoned and which then rot away). This danger can easily be avoided by providing a heavy instantaneous stocking rate which is lifted after a short period of time. For example, 0.35 ha of cactus with a forage biomass of 30 t/ha of green matter will be consumed in one week by a herd of 250 sheep, with a utilization rate of 60%.
Some species, including Faidherbia, Acacia tortilis, A. nilotica indica, Prosopis spp. and Ceratonia, are primarily used for their fruit. It is then advantageous to gather the ripe fruit which falls to the ground and to store it after air drying. Naturally this means that the animal should be kept off the plantations during the harvest.
Several utilization methods produce at one time or another fairly large quantities of firewood, the value of which is often comparable to the feed value. In the case of Leucaena, which is used for the manufacture of leaf meal, the wood can be used for fuel to provide the energy required for the drying and processing of the products (see the contribution by Beale in the Proceedings of this symposium).
The amount of time which the utilizations last depends on intrinsic factors such as the biology of the species under consideration, as well as extrinsic factors such as the environment, the occurrence of severe droughts, unexpected cold, flooding, etc, but above all on the management and utilization method applied.
Generally speaking trees have a productive life of 100 years or more. Shrubs generally remain productive for less long. Nevertheless I have seen plantations of cactus 80 years old which are still productive, as well as plantations of Atriplex nummularia and of A. halimus and Medicago arborea aged over 40 years which have been utilized every year since their initiation. The worst danger lies in too early a utilization before the plants have reached the adult stage, for example, l to 3 years for Atriplex, Medicago arborea, Coronilla glauca, Leucaena, Phyllodineous acacia etc, 4 to 8 years for Cacti, Prosopis spp., Acacia senegal, 12 to 25 years for larger trees such as Faidherbia, Olea, Ceratonia, Gleiditschia, Robinia and Morus. It should be noted that some species of dwarf mulberry from Japan can be established in very dense plantations with several hundred thousand stocks per hectare. These can be utilized by mowing and cut-and-carry systems (M. Schenk, pers. comm., 1966).
The feed value varies very considerably as a function of the species considered, the parts of the plant concerned (fruit, leaves or branches), the phenological stage of the plant or plant parts when consumed by the animal; to these intrinsic factors may be added others linked to the animal, such as selectivity, ingestibility, digestibility, type, age and the physiological condition of the animal, feeding habits, etc. .
The best method for measuring feed value is to measure animal performance under a feeding regime wholly or partially consisting of the feed to be tested. Current chemical analyses alone are totally inadequate.
Some browse forages are comparable to the best grass feeds, for example Leucaena leucocephala leaves and meal, the leaves of Morus alba and Medicago arborea, as well as several species of acacia (but not all).
Some are extremely rich in protein and/or in non-silicate minerals, such as several of the African Capparidaceae (Maerua, Cadaba, Boscia Crataeva, Capparis,) Salvadora persica etc.
Some species or groups of species are deficient in some elements or too rich in others: cacti are very poor in protein but too rich in oxalates. Atriplex are well furnished with protein but too rich in salts, especially NaCl. For further details see the summary on the feed value of browse forages in the Sahel and Sudanian zone of West Africa included in the proceedings of this symposium, as well as the paper on browse forages in North Africa, and the contributions of Harrington and Wilson and Dicko-Touré on the methods of measuring second production and the feed value of browse forages.
Generally speaking it may be said that browse is rich in protein (12% of crude protein on average), in minerals (10%, of which 8% non-silicate and 2% silicate) in B carotene (over 150 mg/kg, and sometimes over 500 mg/kg, as in the case of Leucaena, for example). The net energy content evaluated on the basis of digestibility averages 3 MJ/kg FM (0.42 FU) and is therefore moderate to low. However it varies very considerably, with a dry matter digestibility coefficient of about 50% on average, varying from less than 30% to over 70% according to the species, the part of the plant and the phenological stage. The net energy content thus varies in the same proportions of 2 to 6 MJ/kg DM (0.28 to 0.86 FU/kg Dm).
The agricultural value of forage trees and shrub plantations as stabilizers of grazed ecosystems is universally acknowledged. The establishment and management of these plantations involves a set of techniques derived from agroforestry, although of course the latter is not limited to those species which are purely of interest for browse purposes. Many species used in agroforestry nevertheless have a browse value. For further details see the contribution on the role of agroforestry in the maintenance and improvement of fertility and productivity of soils in the semi-arid zone, included in the proceedings of this symposium.
It may be generally stated that forage tree and shrub plantations are an efficient and relatively inexpensive method for controlling, reducing or eliminating soil erosion, whether by water or wind.
It has also been shown that plantations increase the organic matter content of the soil and hence improve its structural stability, permeability and as a result its water-preservative role.
In many cases and especially on poor, sandy, siliceous, and moderately leached or acidic soils, plantations play a very important part in the cycles of geobiogenic components such as N, P, K, Ca, Na, Mg, S and sometimes also trace elements such as Zn, Cu, Bo, Mo and Co.
The example of Faidherbia albida in West Africa and of Prosopis cineraria in India are particularly well documented in the respect. Millet harvests (Pennisetum typhoides) are 2.5 to 3 times higher, without chemical fertilization, in fields planted with Faidherbia, as against yields obtained from crops planted in the full face of the wind without being combined with this tree species. In Rajasthan the proportions are roughly the same in millet fields with and without Prosopis. Restoring soil fertility by rotating Acacia senegal and sorghum (Sorghum sudanense) in Sudan is also an agroforestry tradition which is well established and documented. The same may be said of the stable agropastoral systems found in Dehesa in southern Spain and the Montado area of Portugal, in which mixed live
stock raising of sheep and Iberian pigs is made possible by a mixed cropping and grazing system in which acorns are used (Quercus iles, Q. faginea, Q. suber).
In the arid zones a number of browse trees and shrubs are planted to fix and stabilize sand dunes and combat wind erosion and desertification. Amongst them: Acacia cyanophylla, A. salicina, A. ligulata, A. raddiana, A. senegal and A. nilotica subps arabica, as well as Calligonum comosum, Haloxylon persicum, Haloxylon aphyllum, Opuntia ficus-indica and Atriplex canescens.
The reconditioning of saline or alkaline soils rendered such by defective agricultural practices (either dryland or irrigation farming), such as are found in the Australian scalds and on other land made sterile by overcropping, can be carried out by using halophilic browse species such as Atriplex nummularia, A. halimus, A. lentiformis, A. semibaccata, A. glauca, A. vesicaria, A. rhagadioides etc. (Beadle, 1948, 1950; Condon R.W., 1960; Malcolm, 1966, 1969, 1971; Gross, 1952; Franclet and Le Houérou, 1971; Jones, 1966, 1967, 1969; Knowles 1954; Smith and Malcolm, 1959; Stannard and Condon, 1958, 1959; Hamilton and Lang, 1978).
The same species have been used for irrigated forage production using water or soil which is too salty for conventional agriculture, for example by using water with an electrical conductivity of 10 to 20 mmhos/cm, such as the water draining from the Gabes and Gafsa Oases, in 1963-66 (Le Houérou, unpublished).
The agricultural role of browse plantations is not limited to maintenance for the reconditioning of soil stability, fertility and productivity. They also play a very important part in stabilizing and diversifying output. They provide or improve the stability of production by supplying cheap feeds during scarcity or drought periods, enabling herd productivity to be maintained. Naturally this also enables the diversification of production in mixed agropastoral or agrosylvopastoral production systems, and consequently an improvement of the cash flow of the farmer or peasant. The latter thus have a more or less continuous cash income throughout the year instead of a single annual lump sum at the time when the main or only crop is harvested. This is particularly true in the semi-arid zone, where the peasants often practice monoculture and are thus subject to exploitation by speculators, precisely because of this irregular cash flow. Browse forages and agroforestry in general are thus able to play a fairly important indirect part in the socio-economic equilibrium of peasant production systems. Browse plantations are thus a potentially powerful tool in rural reconstruction programmes based on an adapted, balanced agricultural system which is stable and productive in the long term (Monjauze and Le Houérou, 1965).
In contrast to annual or biennial species, or even to grass species in general, ligneous species are characterized by a relatively regular, if not constant, interannual production. As such they provide a stabilizing element in pastoral or agropastoral systems.
This regularity can be explained in terms of the structure and biology of these species. Their root system, which is generally powerful, plays a particularly important role. The roots of trees and shrubs can often penetrate to a depth of 10 m (Atriplex halimus) and sometimes well beyond (Faidherbia albida > 30 m), while live roots of Ziziphus lotus 0.5 cm in diameter were found in the arid zone at a depth of 60 m in southern Morocco (Nègre, 1959).
This powerful root system enables these species to reach levels of the subsoil in which water is present, which are inaccessible to grass species, enabling them in particular to make use of ground water at a fairly deep level (10 to 40 m in many cases). The root systems and sometimes the trunks can also provide an important source of water (Cacti, Baobab, Sterculia, Bombax, Brachychyton).
The perennial nature of these species also enables them to use early or late rainfall or rainfall occurring at unseasonal times, which often represents considerable quantities, reaching and sometimes exceeding 20 to 30%e of annual precipitation. Early, late or unseasonal rainfall cannot generally be used by annual or grass species and in the absence of ligneous plants it is lost by evaporation or leaching.
Other species possess the ability to absorb atmospheric humidity through their phyllodineous or cladodial leaves, especially when atmospheric humidity is close to saturation point (usually during the night). These species then preserve a large proportion of this moisture during the hot hours of the day, by closing their stomata. This is the case for Prosopis (P. juliflora and P. chilensis), especially for P. tamarugo (Sudzuki, 1969), for cacti and probably for Parkinsonia aculeata.
Other species also have a highly dispersed surface root system and are thus able to capture minute quantities of moisture on the surface of the soil (drizzle, dew and hidden condensation). This is the case for olive trees, cacti, Calligonum, Haloxylon and many psammophytes. Browse plantations, usually established on good soil, are often highly productive and production of 20 to 30 t of DM/ha-1/year-1 for spineless cacti have been cited, although they are more usually around 3000 to 10000 kg/ha–1 /year–1 (Monjauze and Le Houérou, 1965). Atriplex plantations in North Africa and the Near East produce 1250 to 5000 kg of DM/ha–1/year–1 of forage (Franclet and Le Houérou, 1971; Le Houérou, 1975). Plantations of phyllodineous acacia (A. cyanophylla, A. salicina, A. victorfae and A. ligulata) have a forage production of 1500 to 6000 kg of DM/ha–1/year– 1.
Plantations of tree Lucerne in the semi-arid zone produce 3000 to 6000 kg of DM/ha–1/year–1 (Hamrouni and Sarson, 1974). Olive trees produce 1000 to 3000 kg of DM/ha-1/year-1 of leaves and twigs (Le Houérou, 1962). Generally speaking well established and managed plantations have an annual per hectare production of 5 to 10 kg of consumable DM for each mm of rain fallen. In the tropical African zone production data on plantations are much more rare and frequently the data are unreliable, having been obtained as isolated occurrences in time and space. A classical example of this is the production of Faidherbia albida pods. The literature gives figures of 50 to 150 kg/tree/year for individual adult trees. But it should be made clear that these figures have been obtained (generally on tall untrimmed trees) by single measurements during a specific year. When a colony of Faidherbia is studied over several years figures which are a great deal more modest are obtained, owing to seasonality and the genetic heterogeneity of the colonies: 7 to 10 kg of DM/ha–1/year–1 (Cissé, 1978,1979 and 1980). Admittedly the colonies studied (Segou, Markala and Mopti) consisted of trees which were subject to periodic trimming. The foliage production, which is about the same as the pod production, should therefore be added. It is therefore highly probable that the interannual average for a nontrimmed colony of Faidherbia is more likely to be in the order of 20 to 25 kg/tree–1/year–1 than the 80 to 100 kg suggested by the literature (in zones receiving 400 to 800 mm of average annual rainfall, thus the southern Sahelian and northern Sudanian zones). At 20 kg/tree/year, at a rate of 50 trees per hectare, production would thus be 1000 kg/ha–1/year–1, i.e. a carrying capacity of 2.5 sheep/ha–1/year–1, or 0.5 TLU/ha–1/ year–1.
In the arid and semi-arid zones of West Africa, plantation shrubs can produce 0.5 to 2 kg per year, or 500 to 2000 kg of consumable DM/ha–1 /year–1 (Le Houérou, 1980; Lepape, 1980; Hamel, 1980). The figures were obtained on Parkinsonia aculeata, Prosopis juliflora, Acacia linarioides, A. holosericea A. pyrifolia and A. tumida, giving 2 to 5 kg of DM/ha-1 /year-1.
In the subhumid and humid African tropics production of Leucaena is from 6 to 12 t of DM/ha–1/year–1 of forage (Savory and Beale, 1980; Taylor, 1980).
In the Guinean derived savanna zone of Ivory Coast, Audru (1980) cited a production system combining Leucaena and Panicum maximum which was economically viable and socially suitable for extension to peasants. It used a carrying capacity of 2 TLU (500 kg) per ha, or 1 TLU/ha when a combination of Leucaena and Brachiaria ruziziensis was used.
Damage in plantations can be important in terms of area and time. The main enemies to plantations are easily domestic animals, especially goats and camels. It is therefore essential to protect plantations by effective enclosures (barbed wire or live hedges). Wild herbivores can be a limiting factor in some areas of East or southern Africa. The main pests encountered are:
Plant parasites: Phoelipaea (Orobanchaceae) on Atriplex, a root parasite; Loranthaceae on Acacia: Tapinanthus spp.
Insects: Acrididae. Weevils (on the fruit of African acacias, especially A. tortilis); Cochenilles: Dactylopius opuntiae on cacti; Lepidoptera: the cactus moth: Cactoblastis cactorum.
Mammals: Rodents' Psammomys obesus on Atriplex and cacti.
Browse species almost always consist of populations which have not been subjected to any genetic selection or manipulation by man. Many of them (although not all) are highly heterogeneous as regards their desirable properties in terms of feed, for example:
a) palatability;b) ratio of leaves to stem;
c) chemical composition and nutritive value;
d) fruit bearing potential and quality of fruit.
Highly interesting preliminary work has been carried out, for example in Greece by Liacos et al on Quercus coccifera (see Proceedings of this symposium). Another example is the selection of an Atriplex halimus ecotype with high palatability in Tunisia (no 70100) by Sarson. Further examples are given by Felker using American Prosopis spp. (see Proceedings of this symposium) where the author found very great differences according to origin as regards attributes such as fruit production, sugar content of fruit, etc. The work of Plummer on Atriplex canescens has shown the extraordinary diversity of this taxon.
It seems obvious that, in the future, attention will have to be focused on the selection of provenance, ecotype or cultivars in accordance with certain criteria relating to productivity, quality, palatability/ingestibility nutritive value, ecological adaptation, amongst the species already cultivated.
But there also exists a relatively high number of species which appear to be of great potential interest but are not yet chosen for planting in North Africa; these are: Artemisia herba alba, Hedysarum argentatum, Cytisus arboreus, C. mollis, Echiochilon fruticosum, Gymnocarpos decander, Withania frutescens, Colutea istria, Cytisus battandieri, C. triflorus, Periploca loevigata, Coronilla valentina, Fraxinus excelsior, and Chenopodium auricomum (Australia).
In tropical arid and semi-arid Africa the following are of interest: Acacia tortilis spp. tortilis, raddiana, spirocarpa, heteracantha, Combretum aculeatum, Bauhinia mfescens, Ziziphus mauritiana, Baphia baequartii, Colophospermum mopane, Brachystegia spiciformis, Maerua crassifolia, Cadaba farinosa, Canthium bogoensis, Ormocarpum trichocarpum, Justicia salvioides, Markhamia obtusifolia, Boscia minimifolia, Cordeauxia edulis, Pterocarpus lucens.
Amongst exotic species there are grounds for researching the species of the arid and semi-arid zones of India and Northeastern Brazil for tropical zones, as well as southern and western Australian species, together with those of California and Central Chile for the Mediterranean zone.
It is also relevant to note that some species which behave remarkably well in their natural habitat have always given mediocre or negative results when removed from this range. This is especially true of the argan tree (Argania sideroxylon) and of the tamarugo (Prosopis tamarugo). Similarly, Maireana sp. (Kochia), although well developed in southern Australia have always given poor results in North Africa. Other species, on the other hand, adapt very well outside their own spontaneous habitat, amongst which many Atriplex, Acacia, Morus and Vitis sp., Prosopis juliflora, Cacti, Parkinsonia and Leucaena. Many of these do not reseed spontaneously outside their natural habitat although they may develop excellently. This is the case for Atriplex nummularia and for most of the phyllodineous Australian acacias. The latter characteristic is at one and the same time a disadvantage, in terms of regenerating plantations, and an advantage, since it avoids the risk of invasion. Prosopis juliflora has become an aggressive invader in some areas of Rajasthan, as also some species of cacti in southwestern Madagascar, southern Africa, eastern Ethiopia and Australia.
The gaps in knowledge are many as regards feed value for many of the species used in managed plantations or natural populations. Knowledge is also inadequate as regards the genetic variability of the main species, their biology and their reaction to various management methods such as trimming, lopping, pruning and cutting back.
For Faidherbia albida, which is without doubt the best known Afro-tropical species, almost nothing is known on the best management and utilization methods. Is it more advantageous to use it for its fruit or for its leaves and wood? What is the optimal periodicity for trimming, lopping and pruning?
Consequently, the priorities for research should be focused on the following:
a) nutritive value, ingestibility, digestibility, animal performance;b) biology and reaction to various management methods;
c) genetic variability and research on strains or clones meeting certain production or adaptation criteria.
Audru J., (1980). 'Les ligneux et sub-ligneux fourragers et fruitiers en zone guinéenne; leurs perspectives d'emploi en élevage'. Colloque, International Ligneux Fourrogers en Afrique, Addis Abéba, CIPEA.
Beadle N.C.W., (1946). 'Saltbushes'. J. Soil Cons. NSW, 2,124–129, 137–141.
Beadle N.C.W., (1946). 'Studies in wind erosion. Part IV: Reclamation of scalds'. J. Soil Cons. NSW, 4, 30–35, 64–68, 123-124, 160–170.
Beadle N.C.W., (1952). 'Studies in halophytes. I: The germination of the seed and establishment of seedlings of five different species of Atriplex in Australia'. Ecology, 33, 49–62.
Beale C.I.A., (1980). `Economic aspects of developing Leucaena as a cash crop. A review of pre-investment studies in Malawi, 1974–79'. International Symposium on Browse in Africa. Addis Ababa, ILCA.
Charreau C. et Vidal P., (1965). 'Influence de l'Acacia albida sur la nutrition et les rendements des mils Pennisetum'. L Agron. Trop. 67, 600–626.
Cissé M.I., (1978-1979). 'Les ligneux'. In: Hiernaux, Cissé et Diarra, Rapport annuel de la section écologie, diff. restr. Bamako, CIPEA/Mali.
Condon R.W., (1960).'Scald reclamation experiments at Trida'. J. Soil Cons. NSW 16, 4, 288–302.
Contreas D., (1978).'El presente Estado de conocimiento sobre el Tamarugo'. Mimeo, Santiago, FAO.
Correa da Souza A., (1963). 'Reviao de conhecimentos sobre as palmas forrageiras'. Inst. perq. Agri., Bol. no. 5 Recife.
De Kock, G.C., (1967). 'Drought resistant fodder crops'. Proceedings Grassland Society South Africa 2, 147–156.
De Kock, G.C., (1980). 'Drought resistant fodder shrub crops in South Africa'. Symposium on Browse in Africa, Addis Ababa, ILCA.
Dumancic D., Le Houérou H.N., (1980).'Acacia cyanophylla Lindl. comme fourrage complémentaire pour les petits ruminants en Libye'. Colloque international ligneux fourragers en Afrique. Addis Abéba, CIPEA.
El Hamrouni A., Sarson, M., (1974). 'Valeur alimentaire de certaines plantes spontanées ou introduites en Tunisie'. Note de Recherche no. 2. Inst. Nat. Rech. Forest. Tunis.
El Hamrouni A., Sarson M., (1975). 'Appétabiité de certains Atriplex spontanés ou introduits en Tunisie'. Note de Recherche no. 8. Inst. Nat. Rech. Forest. Tunis.
El Hamrouni A., Sarson M., (1976). 'Résultats d'un essai de charge sur une parcelle de Medicago arborea L'. Note de Recherche no. 14, Inst. Nat. Rech. Forest. Tunis.
Felker P., et al (1980). 'Nitrogen cycling — water use efficiency interactions in semi-arid ecosystems in relation to Management of tree legumes (Prosopis)'. International Symposium on Browse in Africa. Addis Ababa , ILCA.
Forti M., (1971). 'Introduction of fodder shrubs and their evaluation for use in semi-arid areas of the Northern Negev'. Mimeo, Negev Inst. for arid zone res., Beer Sheva.
Franclet A., Le Houérou H.N., (1971). 'Les Atriplex en Tunisie et en Afrique du Nord'. FO: SF/TUN 11, Rapp. Techn. no. 7. Rome FAO.
Griffiths D., (1906). 'Feeding prickly pear to stock in Texas'. Bur. Anim. Industry, Bull, no. 91, Washington D.C.
Hadri H., (1980). 'La plantation d'espéces fourragers dans les projets de mise en valeur pastorale en Libye'. Colloque International sur les ligneux fourragers en Afrique, Addis Abéba, CIPEA.
Hamel O., (1980). 'Acclimation et utilisation des Acacia à phyllodes, d'origine australienne au Sénégal'. Coll. Ligneux Fourr. en Afrique. Addis Abéba, CIPEA.
Hamilton G.J., Lang R.D., (1978). 'Reclamation of dryland salt affected soils'. Soil Cons. NSW, 34, 1, 28–36.
Imperial Agricultural Bureau, (1947).'The use and misuse of shrubs and trees as fodder'. Joint. Public. no. 20 Aberystwyth. Imp. Bur. of Past. and Fodd. Crops.
Jones R.M., (1966).'Scald reclamation studies in the Hay district. Part I: Natural reclamation of scalds'. J. Soil Cons. NSW, 22, 3, 147–160.
Jones R.M., (1967). 'Investigations of seedling establishment on a reclaimed scald'. J. Soil Cons. NSW, 23, 3, 187–191.
Jones R.M., (1969). 'Scald reclamation studies in the Hay district. Part IV: scald soils: their properties and changes with reclamation'. J. Soil Cons. NSW, 25, 1, 104–120.
Jones R.M. ed., (1970). 'The biology of Atriplex'. Proceedings Deniliquin Symposium, Div. Plant Industry CSIRO, Canberra.
Knowles G.H., (1954). 'Scald reclamation in the Hay district'. J. Soil Cons. NSW, 10, 3, 149–156.
Le Houérou H.N., (1971). 'The useful shrubs of the Mediterranean basin and the arid tropical belt south of the Sahara'. Mimeo, AGPC, Misc./24, Rome, FAO.
Le Houérou H.N., (1975). 'Report on a consultation mission to the Range Organization of Iran'. AGPC, Misc. Rome, FAO.
Le Houérou H.N., (1978). 'The role of shrubs and trees in the management of natural grazing lands'. Position paper Item no. 10, VIIIth World Forestry Congress, Jakarta.
Le Houérou H.N., (1979). 'Agroforesty techniques for the conservation and improvement of soil fertility in arid and semi-arid zones'. Proceedings Symposium on Integration of Research to the Valorization of Natural Biological Resources. Rome, Istit. Italo-Latino Americano.
Le Houérou H.N., (1980). 'Rapport de mission aux îles du Cap Vert'. FOD, Rome, FAO.
Lepape M.C., (1980). 'Les fourrages ligneux aux îles du Cap Vert étude préliminaire'. Colloque International sur les ligneux fourragers en Afrique. Addis Abéba, CIPEA.
Liacos L.G., Mouopulos Ch., (1967). 'Contribution to the identification of some range types of Quercus coccifera'. Univ. of Thessaloniki.
McKell C.M., (1980). 'Multiple use of fodder trees and shrubs — a world wide perspective'. International Symposium on Browse in Africa. Addis Ababa, ILCA.
Malcolm C.V., (1966). 'Establishment and growth of halophytes for grazing production from saline wasteland in Western Australia'. Proceedings Desert Shrub Symposium Cedar City. Washington D.C. Bur. of Land Mgt, US Dept. of Interior.
Malcolm C.V., (1969). 'Use of halophytes for forage production on saline wastelands'. J. Austr. Inst. of Agric. Sc., March 1969, pp. 38–49.
Malcolm C.V., (1972). 'Establishing shrubs in Saline environments'. In: McKell, Blaisdell and Goodin eds, Wildland shrubs their biology and utilization. USDA Techn. Rep. INT I., Ogden, Utah.
Malcolm C.V., Swaan T.C., and Ridings H.I., (1980).'Niche seeding for broad scale forage shrub establishment on saline soils'. International Symposium on Browse in Africa. Addis Ababa, ILCA.
Monjauze A., Le Houérou H.N., (1965). 'Le Rô1e des Opuntia dans l'économie agricole Nord-Africaine'. Bull. Ec. Nat. Sup. Agric. Tunis, 8-9, 85–164.
Nêgre R., (1959). 'Recherches phytogéographiques sur l'étage de végétation méditerranéen aride du Maroc occidental'. Trav. Inst. Scient. Cherifien, Serie Bot. no. 13, Rabat.
Nemati M., (1978). 'The role of shrubs and trees in the management of natural grazing lands, with particular reference to protein production in Iran'. Mimeo, 8th World Forestry Congress, Jakarta.
Orev. Y., (1972). 'Seeding saltbush astride the margin cultivation in southern Israel'. In: Blaisdell, Goodin and McKell, ed.: Wildland shrubs, their biology and utilization. Ogden, Utah.
Papanastasis V.P., Liacos L.G., (1980). 'Productivity and management of kermes oak brushlands for goats'. International Symposium on Browse in Africa, Addis Ababa, ILCA.
Piot J., (1980). 'Les méthodes de gestion et d'exploitation des fourrages ligneux peuplement naturels et plantations artificielles'. Colloque International sur les ligneux fourragers en Afrique. Addis Abába, CIPEA.
Plummer A.P., (1966). 'Experience in improving salt desert shrub range by artificial planting'. Proceedings Salt Desert Shrub Symposium Cedar City Bur. Land Mgt, Washington D.C. US Dept. Of Interior.
Plummer A.P., Christensen D.R. and Monsen S.B., (1968).'Restoring big game range in Utah'. USDA For. Ser. Pub. no. 68–3.
Robertson A.G., (1980). 'Research being undertaken in the Atacama desert of Chile on the Tamarugo tree: Prosopis tamarugo Phil'. International Symposium on Browse in Africa, Addis Ababa, ILCA.
Savory R., Breen J.A. and Beale C.I.A., (1980). 'Leucaena as a forage crop on small farms in Malawi'. International Symposium on Browse in Africa. Addis Ababa, ILCA.
Smith S.T., Malcolm C.V., (1959). 'Bringing wheat belt salted land back into production:'. J. Dep. Agric. W. Austr., 8, 3, 263–267.
Springfield H.W., (1970). 'Germination characteristics of Atriplex canescens seed'. Proceedings 11th International Grassland Congress.
Stannard M.E.; Condon R.W., (1958). 'Studies on Trida regeneration area'. J. Soil Cons. NSW, 14, 3, 159–176.
Sudzuki H.F., (1969). 'Absorption foliar de humedad atmosferica en Tamarugo'. Bol. Tech. no. 30, Santiago, Université de Chile.
Taylor M. S., (1980). 'Initial performance of Leucaena at a sub-humid mid-altitude location in Ethiopia'. International Symposium on Browse in Africa, Addis Ababa, ILCA.
