The shrublands of North Africa cover about 940,000 km2, of which 65,000, 350,000 and 525,000 km2 are located in semiarid, arid and desert regions, respectively (Le Houérou, 1989a). They provide both a valuable grazing resource, because of their nutritive value and palatability, and prevent soil erosion by increasing soil stability. According to Le Houérou (1989a), grazing represents 60 to 80% of the economic output of North African shrublands. Used as fodder, trees and shrubs supply a greater amount of protein to livestock on a year round basis. In addition, browse plants are comparatively high in phosphorus but relatively low in energy-supplying constituents.
CONTRIBUTION OF FODDER TREES AND SHRUBS TO LIVESTOCK DIETS
The contribution of browse to the livestock diet varies with the nature of the ecosystem. In less favorable environments, where the grazing season for vegetation is short, the contribution of native fodder shrubs to the animals' diet is very high and may exceed 70% (high mountain, steppe and desert ecosystems). In more favorable areas, shrubs are generally used on a seasonal basis.
SHRUBLANDS OF THE SEMI-ARID TO HUMID ECOSYSTEMS
In the semi-arid to humid ecoclimatic zones of the N. African countries, the major natural shrubland ecosystems are dominated by Quercus spp. (3.47 million hectares), Cedrus atlantica (0.15 million hectares), Pinus halepensis (1.27 million hectares), Tetraclinis articulata (0.94 million hectares), Olea europea, Ceratonia siliqua, Pistacia lentiscus (0.72 million hectares), Juniperus phoenicea (2.3 million hectares), and 0.7 million hectare parkland of Argania spinosa (Le Houérou, 1989a).
The High Atlas study case
In the High Atlas, farming systems integrate both agricultural and pastoral components in which fodder trees play an important role. Crops are cultivated on farms with an average size of 0.5 ha. Small ruminant feeding systems are based on pastoral resources which provide 94% of small ruminant energy requirements (Bourbouze, 1982). Pasture grazing, especially for small ruminants, comes primarily from watersheds which are public lands.
The main fodder trees in the watersheds are Fraxinus xanthophyloides, Quercus rotundifolia and Juniperus oxycedrus. The shrubs used as fodder are Cytisus spp., Globularia mainii, Ormenis scariosa, Genista spp. and Thymus spp.
The nutritional quality of these fodder trees varies among species. Fraxinus xanthophyloides has a good nutritional quality (0.8 feed units (FU)/kg DM, and 15% crude protein in DM) and is an important source of both energy and protein. The nutritive values of Quercus rotundifolia and Juniperus oxycedrus are low in comparison to Fraxinus xanthophyloides. Quercus rotundifolia and Juniperus oxycedrus average 8 and 5% crude protein and ash in DM, respectively. Quercus spp. is rich in phenolic compounds such as tannins which result in a decrease in digestive utilization. El Honsali (1982) compared the use of oak leaves, highly rich in tannins, by sheep and goats. He concluded that infusion of tannins slightly improved dry matter intake for goats whereas it had an adverse effect on sheep.
In the High Atlas, Bourbouze (1982) shows that the contribution of fodder trees and shrubs to goat diets remains high, except in July (Figure 1). Among fodder trees, Quercus rotundifolia, despite its low nutritive value, contributes the most, from both leaves and acorns, i.e, 86% in January. Indeed, during periods when food is short (winter), shoots or branches of Quercus ilex are cut by herders and provided to goats. The use of more Juniperus oxycedrus in goat diet is compromised by the presence of spines.
Trees and shrubs used as fodder provide a sufficient amount of protein to meet goat maintenance requirements year-round (Figure 1).
FIGURE 1. Diet botanical composition of goats (A) and contribution of range feed resources to cover goat maintenance requirements (B) in the High Atlas of Morocco (Bourbouze, 1982).
Halophytic steppe and desert regions
Feeding systems in these regions, characterized by a pre-Saharan climate where the precipitation averages 70 mm/year at most, are based exclusively on open range feed resources since supplementary feeds are rare. The open ranges are used by herds of dromedaries in grazing patterns based on seasonal and yearly movements. Seasonal movements among regional grazing areas ensure forage balance and water availability. Yearly decisions concern environmental conditions (climatic crisis, droughts) and the political boundaries of the different countries.
The three major shrublands are: 1) crassulescent halophytic steppes, 2) nanophanerophytic steppes and 3)wormwood sub-desertic steppes. The crassulescent halophytic steppes with Salsola spp., Suaeda spp., Arthrocnemum indicum and Salicornia spp. cover 4 million hectares. The nanophanerophytic steppes with Ziziphus, Atriplex, Calligonum and Tamarix and wormwood sub-desertic steppes, dominated by Haloxylon, Anabasis and Traganum, occupy areas of 2 and 3 million hectares, respectively (Le Houérou, 1989a).
Trees and shrubs of these halophytic steppes survive a higher water stress and tolerate various amounts of salt in the soil. They supply the majority of protein to livestock, especially dromedaries and goats. The crude protein contents of these halophytic plants are high and remain stable throughout the seasons. The crude protein content in DM of Acacia raddiana, legume tree, and Traganum nudatum varies from 11% to 19% during the early and late season, respectively. Calligonum comosum and Salsola spp. have lower protein levels. Ash content in DM of the halophytic species is extremely high. It varies in autumn from 19% for Haloxylon scoparium to 45% for Traganum nudatum. Moreover, in vitro dry matter digestibility coefficients are adequate (45 to 55% of DM on average). These levels should, however, be considered with caution because of the high ash content which might lead to a reduction in the metabolizable energy of these forages. These trees and shrubs are chiefly grazed by dromedaries.
|Botanical composition (in %)|
|Crude protein (% DM)||12.60||13.59||19.63||10.94|
|NDF (% DM)||33.11||38.24||42.34||33.82|
|ADF (% DM)||25.39||30.57||31.22||26.25|
|ADL (% DM)||11.82||10.88||7.30||8.19|
|In vitro dry matter digestibility (% DM)|
A study carried out in the southern steppe of Morocco indicates that the diet of dromedaries is from fodder trees, fodder shrubs and herbaceous plants (Moumen, 1991). Contributions of the different species vary depending on the grazing season (Table 1). Early in the season, Salsola spp. and Traganum nudatum average 43.7 and 36.5%, respectively. In spring, dromedaries include more herbaceous plants in their diet whereas, in summer, they ingest mainly Diplotaxis harra (67.7%) and Traganum nudatum (14%). Late in the grazing season, fodder trees and shrubs become the only dietary component and average 71 and 25%, respectively.
The botanical composition of the diet is dominated by fodder trees and shrubs resulting in a high crude protein content year-round (Table 1). The values for in vitro dry matter digestibility are adequate early in the season and become low thereafter. Digestibility coefficients, expressed on an organic matter basis, are much lower because of the high ash content of the available halophytic species.
Total dry matter consumption averages 10.6, 13.8, 12.00 and 10.9 kg/animal/day in January, April, June and October, respectively (Moumen, 1991). Total consumption is lower both early and late in the season because of the low availability of herbaceous plants. Dromedary production averages 198 kg of live meat and 580 kg of milk per animal unit per year.
The climate in the chamaephytic steppes is arid with an average precipitation of 200 mm. It is characterized by a pulse of precipitation and a large number of years with precipitation below average. The major North African shrublands are Artemisia herba alba steppe (7 million hectares) on silty soils and Artemisia campestris (4 million hectares) on sandy soils (Le Houérou, 1989a).
In these steppes, sporadic cultivation makes the farming systems more and more agropastoral. Three different types of resources contribute to feed small ruminants, i.e., range forages, agricultural by-products (straw and stubble) and supplementary feed. El Aich (1987) found that 40% and 15% of the animal needs were provided by Stipa tenacissima and Artemisia herba alba in normal and dry years, respectively. Artemisia herba alba communities are used as spring pastures by sheep producers.
Aerial phytomass production of the Artemisia plant community averages 200 to 250 kg DM/ha (Merzak, 1990). Artemisia herba alba averages crude protein contents of 12 and 9% early and late in the season, respectively. Ash levels remain high (> 19%) regardless of the period of the year (Merzak, 1990). Despite their mean digestibility coefficients (49%), Artemisia spp. have high content of essential oils which interferes with the energy assimilation. Cook et al. (1952) reported that the metabolizable energy in Artemisia tridentata is lower because of the essential oils; its metabolizability is of the magnitude of 0.30 as compared to alfalfa hay, 0.82.
A study conducted on the oriental steppe of Morocco indicates that sheep ingest a large proportion of Artemisia herba alba and the other shrubs, especially during periods of drought (Table 2). Artemisia herba alba contribution is 76.5 % on average.
However, sheep respond quickly to changes in range botanical composition resulting from concentrated rain. In the Artemisia spp. community, sheep ingest a diet rich in cell wall content, with an adequate level of protein (Table 2). The average ratio ADL/ADF of 45.6% indicates a depressed digestion of the fibre fraction. In vitro organic matter digestion coefficients of sheep diets are low whereas dry matter intake levels are acceptable (Table 2) and allow an average gain of 100 g/day during spring for yearling rams (Merzak, 1990).
Unregulated and selective grazing by livestock has shifted many Artemisia spp. communities to a situation where unpalatable forbs or aggressive shrubs of low palatability dominate. In addition, sporadic cultivation and uprooting make the extent of desertification serious. As results of shrubland depletion, feeding calendars for small ruminants experience a shortage of feed in summer and autumn, especially in dry years.
|Early spring||Mid-spring||Early summer|
|Botanical composition (in %)|
|Artemisia herba alba||78.05||68.55||82.95|
|Ash (% DM)||11.32||15.09||9.47|
|Crude protein (% DM)||7.55||7.90||7.98|
|NDF (% DM)||47.61||48.10||52.28|
|ADF (% DM)||36.41||34.79||36.25|
|ADL (% DM)||14.79||16.61||17.59|
|In vitro organic matter digestibility (% DM)|
Strategies for improving shrubland productivity and use depend on the nature of the ecosystem. In more resilient ecosystems, i.e., semi arid to humid shrublands, there is a need to keep shrubs and find a way to increase the proportion of high quality preferred food available, relative to animal requirements. Indeed, small changes in forage composition of high quality protein plants are disproportionately important in improving animal status. For instance, a vegetation rest results in an increase in the abundance of preferred species and the standing crop of biomass.
Phosphorus fertilizers are expected to increase phytomass, improve botanical composition and enhance the establishment of legumes.
In a less favorable environment, stands containing high numbers of lesspreferred individuals must be managed to allow the establishment and persistence of preferred genotypes. Proper grazing pressure is the key factor in shrub management. Under higher stocking rates, the density of senescent Artemisia herba helba plants increased and the survival of seedlings decreased.
Plantations of introduced species
Seedling and planting provide an opportunity to include shrub species that will contribute to stability and diversity as well as useful productivity of the ecosystem. Many shrub species were introduced in the region, such as Acacia spp., Atriplex spp., and Prosopis spp. and Opuntia spp. They have been planted over more than half million hectares in Morocco, Algeria, Tunisia, Libya and Egypt. Among these fodder shrubs, Atriplex spp. are the most recommended and frequently planted species.
The ecological value of Atriplex spp.
Atriplex spp. can grow normally with only 150 to 200 mm rainfall and are not affected by heavy textured and high salinity soils and water. Their frost resistance is high. The choice of species is the determinant for establishment of a plantation. Baumann (1990) compared legume shrubs (Acacia spp.) to non-legume shrubs (Atriplex spp.) on the oriental steppe of Morocco. He concluded that the rates of establishment of legume shrubs were very low because Acacia spp. need a mean precipitation of more than 150 mm and deep sandy soils. The rates of establishment of Atriplex varied among species in the range 70–75%. In the same study, Artemisia herba helba used as a control, had the highest survival rates.
The phytomass yield varies with the density of the seedlings. Palatable biomass of Atriplex nummularia (yearling twigs and leaves) averaged 462 kg DM/ha (Tazi et al., 1991). Protection of Atriplex spp. during establishment increases the amount of herbaceous grown beneath and between bushes. There are regeneration problems with Atriplex spp. after 6 to 7 years of utilisation, especially on shallow soils. The average duration for Atriplex nummularia plantation is 8 to 10 years.
Atriplex spp. provide a good palatable fodder year-round, because they keep their foliage. However, animals avoid shrubs in spring when herbaceous plants are available. Palatability studies indicate that introduced shrubs (Atriplex nummularia, Acacia cyanophylla and Medicago arborea) are very low dietary components during the growing season when herbaceous plants are available but, as the season advances, animals ingest more shrubs (Saadani, 1987).
Atriplex nummularia is relatively high in protein and ash. The crude protein and ash contents of Atriplex nummularia average 18.2±0.45 and 22.7±1.31 per cent. respectively. Crude protein content (ash) of Acacia cyanophylla average 13.5 (10.0), 10.4 (9.2), and 11.07 (11.9) for spring, summer and autumn, respectively. The mean ratios of ADL/ ADF (>50%) indicate a depressed digestion of the fibre fraction. The digestibility of Atriplex spp. averages 59% in spring and 49% in summer, whereas Acacia cyanophylla has lower digestibility, i.e., 26 and 20% in spring and summer, respectively (Saadani, 1987). The intake of Atriplex spp. varies in the interval of 50 to 55 g DM/kgLW0.73. Increased consumption of Atriplex spp. is accompanied by higher water intakes because of the increased water required for urinary excretion of sodium. Sheep grazing Atriplex vesicaria consume 7 to 7.5 kg/day of water in comparison to 3.2 kg/day on grasslands (Wilson et al., 1969). As supplementary fodder, Atriplex spp. should not make more than 25 to 30% of the sheep's diet.
The economical feasibility of Atriplex spp.
The question of the economical feasibility is of central interest. The establishment costs for a plantation (nursery, soil preparation, transport, planting, watering and maintenance) averaged $350 US/ha (Tafrata Perimeter, Morocco) with Atriplex nummularia in 1987. A 30 to 35% supplementary cost should be accounted for as cost of protection. With an average production of 500 kg DM/ha (140 FU), and assuming that the duration of use of the plantations is 8 years, the cost per FU is about $0.45 US. Le Houérou (1989b) suggested that Atriplex plantations can be produced at a moderate cost as soon as yields are over 1000 FU/ha.
The economic viability of Atriplex spp. plantations appear uncertain under North African conditions. However, the value of browse plantations is undeniable if their multitude functions are taken into consideration. The comparison with other range improvements are aspects that answer both the technical validity and the economic feasibility of fodder shrub development.
The social feasibility of Atriplex spp.
Social acceptability must be assessed prior to any range rehabilitation programme. Questions such as: 1) why people prefer certain shrubs and 2) how people assess the value of a shrub, determine the success of the programme.
Feedbacks from shrub plantations are diverse. Shrub plantations are considered as government actions and are subject to lack of confidence from livestock producers. In the east of Morocco, sheep producers prefer rehabilitation with native shrub (Artemisia herba alba). For a technician, Atriplex spp. are planted to serve many purposes. But the message the livestock producer receives does not imply the same reasons. A survey on attitude regarding Atriplex in the Dhamar Montane Plains (DHV, 1989) showed nearly all villagers recognized “salt tree”(shajar al milh) could be grazed by sheep; but they did not mention that Atriplex nummularia can be used for firewood, as a windbreak or for erosion control.
Baumann, M. 1990. Possibilités et limites de l'installation d'arbustes fourragers en vue de l'amélioration des régions steppiques du Maroc Oriental: Reésultats préliminaires. Al Awamia 74: 84–105
Bourbouze, A. 1982. L'Elevage dans la montagne marocaine.g Doctorat d'Ingénieur. I.N.A. Paris-Grignon, 345 pp.
Cook, C.W., Stoddart L.A. and Harris L.E. 1952. Determining the digestibility and metabolizability energy of winter range plants by sheep. Journal of Animal Science 11:578–590
DHV (Consulting Engineers). 1989. From Recommendation to Acceptance. The dissemination of the Atriplex message in the Yemen Arab Republic. Communication No. 31
El Aich, A. 1987. La production agropastorale dans la commune pilote de Ain Beni Mathar. RAB Project, FAO.
El Honsali, A. 1982. Utilisation comparée des feuilles de chêne vert par les ovins et les caprinsg. Mémoire de fin d'étude de l'Institut Agronomique et Vétérinaire Hassan II, Rabat.
Le Houérou, H.N. 1989a. The shrublands of Africa. In: The biology and utilization of shrubs. McKell, C.M. (ed.), Academic Press. pp. 119–143
Le Houérou, H.N. 1989b. An assessement of the economic feasibility of fodder shrubs plantations (with particular reference to Africa). In: The biology and utilization of shrubs. McKell, C.M. (ed.), Academic Press. pp. 603–629
Merzak, S. 1990. Contribution à la définition d'une utilisation a p p ropriée des parcours à Armoise dans l'Oriental. Mémoire de fin d'étude de l'institut Agronomique et Vétérinaire Hassan II, Rabat.
Moumen, I. 1991. Comportement alimentaire et systèmes d'élevage du dromadaire. Mémoire de fin d'étude de l'institut Agronomique et Vétérinaire Hassan II, Rabat.
Saadani, 1987. Production fourragère et comportement alimentaire des ovins et des caprins dans un parcours mixte a Acacia cyanophylla, Atriplex nummularia et Medicago arborea. Mémoire de fin d'étude de l'institut Agronomique et Vétérinaire Hassan II, Rabat.
Tazi, M., Birouk, A., Hafidi, B., and Haimoura, A. 1991. Comportement d'Atriplex nummularia en zone aride du sud marocain. IVth Rangelands Congress, Montpellier, France.
Wilson, A.D., Leigh, J.H., and Mulham, W.E. 1969. A study of Merino sheep grazing a Bladder saltbush (Atriplex vesicaria)-Cotton-bush (Kochia aphylla) community on the Riverine Plain. Australian Journal of agricultural Research 20: 1123–36