Environmental impacts of livestock farming in Sahel.
In West Africa, the interactions among environment, social, economic and political drivers on pastoralism in arid and semi-arid regions of Sahel affect the landscapes changes. To evaluate the impacts of extensive livestock production on the environment, different indicators have been used to quantify emissions of greenhouses gas to air, and nutriens losses to soil and water. Dynamic relationships between social welbeing and ecosystems are considered to describe the pastoral environment. Different simples or composed indicators are reviewed to assess their relevance in the context of pastoral community. Pastoral population represents 12 million in West Africa. They contribute highly to a national and regional economy by supplying livestock, meat, fresh milk, milk products and skins to a large market. Organization of pastoral communities is complex and variable. The dependence to land and climate fluctuations makes pastoralists vulnerable to any change.
Key words: indicators, environment, ecology, socio-economy, policies, Pastoralism
Arid and semi-arid environments are characterized by their extreme variability in terms of land forms, soils, fauna, flora, water balances and human activities (FAO, 1987). Rainfall zones are ranged between 0-300 mm in the arid zone and 300-600mm in semi-arid areas (FAO, 1987). General, rainfall patterns are usually unpredictable and are subject to great fluctuation. One-year droughts are more frequent than multi-year droughts (Sidahmed, 1996). The predominant vegetation consists in steppes and savannas. Extensive Livestock production is the main activity. It contributes significantly to food security, employment and family incomes. It contributes highly to the livelihood of arid and semi arid population. The extensive livestock production is predominantly grazing, which depends on the natural productivity of the rangelands. Different typologies exist to describe the extensive production system. According to Sére et al. 1996, grazing systems are the main system in arid and semi arid areas. It is very sensitive to climate crisis and change. Due to climate change, pastoralists have developed local knowledge to predict and to manage the climate risks. High mobility of livestock such as nomadic or transhumant and large size of herds are adaptation factors for the pastoral system.
The pastoral system regroups the relationship among climate, soils, vegetation, animals and humans. According to Toutain et al. 2010, extensive livestock production affects directly or indirectly the environment by specific pressures. The pastoral population is estimated to 13.3 millions in Africa. They represent respectively 25% and 14% of human population in Western and Northern Africa (Carrière, 1996). Pastoralist societies are organized in different tribal groups and have strong social cohesion. Moreover, herbivores such as bovine, sheep, goats, donkeys and camels are most kept. In North Africa, camels and small ruminants are dominant while in West and East Africa, bovines represent the largest capital. The high population of animals causes a high pressure on soils, rangelands and livelihoods. This livestock system depends often on rainfall, water resources, grasslands availability, droughts and pastoralist social organization.
In this review, environment is defined as the dynamic relationship between pastoral population being and ecosystems. The impacts of pastoral system on the environment such as on ecosystems, social and economy are highlighted. Different indicators exist to assess the livestock environmental impacts. However, indicators should be relevant to help understanding the complexity of interactions factors in pastoral areas. Waltz, 2000 defines an indicator as a variable that describes the state of a system. Heink and Kowarick, 2010, consider indicator as a profoundly ambiguous term that has different meanings in different contexts. Heink and Kowarick, 2010 suggest a definition of indicator for ecology and environmental planning: “An indicator in ecology and environmental planning is a component or a measure of environmentally relevant phenomena used to depict or evaluate environmental conditions or changes or to set environmental goals. Environmentally relevant phenomena are pressures, states, and responses as defined by the OECD (2003)”.
This review will be limited on the environmental impacts of the pastoral system in Western Africa, arid and semi arid areas. The regional agro-ecological zones range from the humid zone (along the coastline) to the dry Sahelian zone (in the north) and roughly define an increasing gradient of dependence on ruminant livestock for livelihoods (Ly et al. 2009). Fernandez-Rivera et al. (2004) have described 15 productions systems in West Africa. Our review is focused on only rangeland-based pastoral systems. The objective is to analyze the indicators available and their relevance for research and policy makers. Many questions should be raise: Do pastoralist care about the environment? What indicators should be used to express pastoralism-environment relations in a way that facilitates improved management?
2. Characteristics of Pastoral systems
The Sahel is a 400 km wide band situated immediately in south of the Sahara desert. The drier, northern part of the Sahel is used for pastoralism, whereas the more humid south is used for mixed farming, involving the integration of crops and livestock (Powell et al. 1996). In Sahel areas of West Africa, the productivity of rangelands, croplands and livestock are inextricably linked. The land use represents 25.1% of West Africa and contains 4.6 million cattle and 24.8 million sheep and goats, equivalent to 8 million tropical livestock units (TLUs; Ly et al, 2009). Livestock holdings of pastoral systems range from a few to hundreds of head per household with varying ratios of cattle, sheep and goats (Wilson, 1986; Swinton, 1988 in Powell et al., 1996). Herd size is often positively related to degree of mobility. The extensive livestock farming system produces live-animals, milk, meat and skins that are sold. Ruminants are the main source of cash for farmers, and are used in religious and funeral ceremonies. Livestock system is characterized by low-input, high mobility, large herds and strong social organization. Considering their dependence to the extent mobility, pastoral system is divided in 2 categories, nomadic and transhumant. The mobility allows the reduction of feed and water shortage (Powell et al. 1996). The mobility imposes a particular social organization in nomadic system. The whole family moves with herds for long distances. The pastoral societies are regrouped in tribal. Each tribe has his own leader. The leader gives advice for the period to move; he has knowledge in lecture of climate variations and helps in how to use the available resources. Pastoral societies are characterized by strong mutual aid. The size of herds in pastoral systems has the primary role to serve as an asset for risk management in addition to the traditional role of providing savings from the wealth stored as animals. In case of climate crisis or disease outbreak, it is possible to reconstitute a herd by passing on animals given to neighbors or family members as loans.
In some regions, due to the increase of crop activities, herd mobility may be reduced, although the loss of rangeland feed may be compensated by the increased quantities of crop residues that become available within the system (Ly et al. 2009). Natural pasture and crop residuals are the principal animal feeds. The crop residues are feed in dry season where pastoralists can have agreements with crop farmers for fertilization with corralling animals in overnight on fields.
Interactions between climate, soils, vegetation, animals and humans have developed over time through different modes of land appropriation and exploitation, often controlled by traditional pastoral organizations. Pastoral areas have thus been subject to livestock mobility to ensure the livelihood of human and animal populations (Ly et al., 2009).
It shows that pastoral systems is found mostly in the arid and dried semi-arid zones where a high risk of crop failure exists, there is a comparative advantage for livestock production, and there is also a ready and growing market for livestock in other adjoining zones. Hence agro-ecology and market forces are key drivers of pastoral production. Because of high herd mobility this system is well adapted to the unpredictable weather and the risk associated with the constant threat of drought. Animal breeds exploited by pastoralists are well adapted to the dry and wet environment. The resistance genes have been developed by natural selection. Today, different Sahel ruminant’s races have been used in crossing with other races to create race with good rusticity such as bovine Senepol in central and Latina America. Senepol is a bovine crossed between N’Dama and Red Pull Races.
3. Indicators for ecological pastoral impacts
Different methodologies were developed to understand the ecological impacts of agriculture activities. They are applied in most case on farm activities not to whole production system with a great variability according to region. However, these methodologies need some adaptation to be used on a pastoral system where production system is characterized by high mobility, large land used and rangeland dependence.
Ecological footprint (EF) analysis compares human demand on nature with the biosphere's ability to regenerate resources and provide services. It does this by assessing the biologically productive land and marine area required to produce the resources that a population consumes and absorb the corresponding waste, using prevailing technology (Wikipedia.com). This method should be applied on pastoral system, according to ecological impact of pastoralism and the dependence of pastoral family on animals and rangelands productivity.
The Input-Output assessment (IOA) is an environment impacts analysis that considers the efficiency use of nutrients, energy and pesticides. It is assessed by farm gate balance which is a nutrient balance between input and output at farm level. Another method is the life cycle assessment (LCA). LCA is a method to analyze the environment impacts of a production system. In livestock system, the system boundary can be defined, for instance, is from cradle-to-gate. It means that all inputs and processes for the feed production are included as well as all the upstream processes necessary to produce these inputs. It considers all items involved such as infrastructure, operation of the machines, fertilizers manufacturing and application, pesticide production and application, field operations, and direct field and farm emissions (Nemecek et al., 2011). Pastoral system as a low-input livestock system is concerned only by directly field operations and animal emission. Indicators used are non-renewable energy resources, global warming potential over 100 years, ozone formation, eutrophication potential (losses of N and P to aquatic and terrestrial ecosystems), acidification potential, terrestrial ecotoxicity potential, aquatic ecotoxicity potential, human toxicity potential, biodiversity and soil quality (Nemecek et al., 2011). Those indicators are applicable to pastoral system in dry-regions; however, their assessment may be questionable because of lack of data addressing pastoral farming system in Sahel.
3.1. Land and soil
The Sahel soils are predominantly by sandy soils very low in organic matter (Pieri, 1989). The compaction is the negative impact of extensive livestock production on soil physical properties (Toutain et al, 2009). Trampling increases soil bulk density and decreases water infiltration rates (in Powell et al., 1996). An indicator used to assess the compaction is the soil apparent density. The soil apparent density is a simple indicator and is easy to measure on-field and in laboratory. It increases with the stocking rate of animal (Humphreys, 1991 in Carrière, 1996). His variation depends on types of soils and seasons. The compacted soils are covered by woody vegetation or shrubs, the herbaceous vegetation are reduced mostly. This phenomenon concurs to loss of native biodiversity. In Sahel zones, this soil degradation phenomenon is found in the saline lands of the delta of Senegal, Naga Chad (Carrière, 1996).
Vegetation removal and trampling by livestock can enhance water run-off and soil erosion (Powell et al. 1996). The risks of wind and water erosion are very high in West Africa Sahel zone. The soil is very dry and vulnerable to violent climate crisis such as rainfall and drought. The soil is not well covered by vegetation. Different soil particles are eroded. The relative erodibility of soil is estimated, a need arose for different soil apparent density for all various fractions that are moved by the wind or by water. The size of fraction eroded by wind is usually appreciably smaller than 2 mm in diameter (Chepil, 1950). The erodibility of these fractions is markedly affected by their apparent density. This indicator needs to be confronted by the evolution of the vegetation recovery that can be considered as an explanatory and predictive variable. The comparison between different satellite images taken at different periods testimonies the amplitude of erosion. In Sahel zone of Burkina Faso, the scattered natural woody vegetations play an important role as wind erosion control strategies (Leenders, 2006).
The extensive livestock is susceptible to increase soil salinity in Sahel region when the stocking rate is increased. The indicators of soil salinity are linked on the presence or absence of certain plants, like the invasion of tolerant weeds. Native tree and shrub species can also be at risk from increasing soil salinity. A good indicator of potential salinity problems is the depth and quality of groundwater. If groundwater is saline and the watertable is shallow or rising, there is the potential for salinity problems to occur in the future (Henschke, 2007).
However, the pastoral system contributes to the landscapes and rangelands management by avoiding of scrub encroachment and forest burning, by fertilization of croplands and rangelands. Treading some soils, may increase soil surface roughness and improve infiltration by breaking soil surface crust (Casenave & Valentin, 1989, Powell et al., 1996, Toutain, 2010).
3.2. Sustainable nutrient use (N, P)
The sandy soils of Sahel are very low nitrogen (N) and phosphorus (P) contents. Extensive livestock plays a key role in nutrient transfer by cycling biomass and use of manure and urine across the landscape (Powell et al., 1996). The estimation of N and P rangeland contents and their export by animal by feces and urine is a good indicator of nutrient balance in Sahel zone. Generally, the balance of nutrients in rangelands is negative. Animal transfer nutrient from rangelands to corralling place or crop lands in dry-season. Repeated loss of nutrients can be the cause of rangeland changes. Moreover, the evolution of rangeland vegetation such as herbaceous, woody vegetation or the occurring of weedy can be associated to this parameter to understand better the impact. Nutrients are wasted through N evaporation and N leaching. NH3 evaporation and nitrates leaching may be assessed to quantify the Nutrient balance in Sahel.
3.3. Air and atmosphere
Extensive livestock production contributes to the increase of the concentration of greenhouse gases in atmosphere. The emission of methane (CH4), carbon dioxide (CO2) and nitrous oxide (NO2) are the most important greenhouse gases from livestock production. Methane is emitted from enteric fermentation or manure. The CO2 is most emitted from animal respiration and forest burning. Ruminants in Sahel emit an important quantity of CH4 because their feed based importantly on fodder. According to Chouinard (2002), the methane emission is respectively 90, 65 and 8 kg per animal per year in bovine, sheep and goat. However, the multispecies grazed plants may contribute to methane reduction by high contents of condensed tannins. Carulla et al., (2005) showed good results in sheep diets with Acacia mearnsii condensed tannins and reduced methane emissions by 12%. The data available are not related to experimentation on livestock production in Sahel. The estimation takes in account the high population of ruminants in West Africa but do not integrate the stocking rate. With stocking rate of 5 TLUs per Km2, the emission per unit of surface may be very lower. Rangelands and soils play an important role in carbon sequestration. In fact, plants absorb an important quantity of CO2 for their photosynthesis. Soil carbon sequestration is the process of transferring carbon dioxide from the atmosphere into the soil through crop residues and other organic solids, and in a form that is not immediately reemitted (Sundermeier, 2005). Moreover, the soil carbon sequestration should be integrated in calculations to estimate the greenhouse gases surplus.
In the Sahel, The distribution of rainfall is between June and October. Rangeland productions are composed by herbaceous, shrubs and trees. Most plants are annual. The C4 grasses, shrubs and small trees are dominant. The woody vegetation is natural scattered. After first rainfall, the vegetation germinates significantly until flowering (Hierneaux, 1993). Grazing reduces standing biomass through forage consumption and associated trampling of vegetation (Hierneaux, 1993; Powell et al., 1996). Heavy grazing is remarked around water points and livestock tracks (Figure 1; Powell et al., 1996).
Hierneaux, (1993) found that grazing biomass on sandy sites don’t affect the vegetation response to changing rainfall. However, sites with silty or shallow soils produce less biomass than clay or sandy sites after moderate grazing in wet season. Different studies have considered overgrazing as cause of rangelands and landscapes degradation and lead to regional climatic desertification (Otterman, 1974; Charney 1975; Chen and Zhu, 2001). This hypothesis has been seriously questioned (Horowitz, 1979; Standford, 1983, Hierneaux, 1993, Nicholson et al., 1998). The indicator used was albedo which is very high on soils denuded by overgrazing and appears bright, in high contrast to regions covered by natural vegetation (Otterman, 1974, Charney, 1975). Nicholson et al., (1998) demonstrated that there has been no progressive change of either the Saharan boundary or vegetation cover in the Sahel during 1980-95 periods. The albedo is a complex problem. The reduction of vegetation cover does not result in higher albedo (Nicholson et al., 1998). The spectrum of satellite image combined with survey on field shows may be a relevant indicator of the variation of vegetation dynamic during season.
The other indicator of rangeland ecosystem health in Sahel is the shift of preferred plants by less palatable ones or by species that cope better with defoliation because of their short growing cycle (Turner, 1992; Hierneaux, 1993; Powell et al., 1996). It is likely to occur around water points, herd rest areas or transhumance pathways, because soils fertility is enhanced by the large amounts of manure and urine deposited (figure 1; Hanan, 1991; Hierneaux, 1993). The less palatable species are dicotyledons such as Zornia glochidiata, Tribulus terrestris, Cassia mimosoides and Sida ssp; short-cycle grasses, such as Tragus bertheronianus and Eragrostis pilosa or long cycle grasses such as Chloris prieurii and Dactyloctenium aegyptiacum. Less palatable plants tend to encroach and reduce forage and nutrient availability (Powell et al., 1996). Moreover, less palatable invasion in south Sahel has been remarked after the 1983-84 droughts, because of changes of floristic composition. It was not influenced by overgrazing (Hierneaux, 1993). It has been a systematic reduction of “productivity” as assessed by the water-use efficiency of the vegetation cover (Nicholson et al., 1998). Invasion of less palatable species does not indicate always the impact of livestock activities on rangelands ecosystem health. However, Hierneaux (1993) showed how the rangelands are very able for resilience after a long period of stress. Livestock contributes highly to germination of some species Balanites aegyptiaca and Acacia raddiana by breaking the dormancy of their hard seeds after a passage through animal’s gut (Hierneaux, 1993). The figure 2 shows the different impacts of pastoral system on rangeland production and the associated indicators.
4. Policies and politics
Swift (1988) stressed that development in the herding economies in Africa has not been successful. There was a feeling among some donors and governments that the problems are too great and returns too low, and those scarce development resources should be redirected to projects offering a better chance of success and higher rates of return. Reasons advanced were social and ecologic. The lack of knowledge of pastoral techniques and rangelands valorization was the principal motivation to limit the investment (Carrière, 1996). Several countries have abandoned the investment on Pastoralism in different rural development projects. However, in Mauritania, the instauration of pastoral law in 2000 has recognized the Pastoralism specifics and proposed institutional frameworks to control his application. It described also the pastoralists right such as mobility, water and land accessibility, respect of transhumance pathways and territory, conflict resolution (Official Journal, 2000). This law has enhanced the several efforts made by Mauritanian government to protect Pastoralism. Niger is another good example. Contrary of above, in Chad, lack of a comprehensive pastoral laws raised multiples conflicts between pastoralists, agro-pastoralists and other land users. Implementing policies requires financial backing, commitment, and administrative and legal arrangements (Øygard et al., 1999). The FAO is assisting the Chad government in pastoral code policy to strengthen pastoral rights (Yosko and Saleh, 2010).
With the consideration of environment in large meaning, our review has clearly explored the different indicators of extensive livestock impacts in Sahel of West Africa. The ecology, sociology, economy and politics and their interaction are the main domains studied in arid and semi-arid regions. In ecology, one indicator is sometimes used to describe a phenomenon in Sahel. This should conduce to hasty and inaccurate conclusions. To understand well the dynamic of Sahel ecosystems, is useful to integrate different indicators. Rangeland variation is not associated only to the overgrazing but also to other variables such as rainfall and soil density. The distribution of herbaceous species, shrubs and trees should be affected by types of soils, season variation and animal digestion. The use of integrated and aggregated indicators is relevant to evaluate the landscape changes in Sahel. The other parameter to integrate is the resilience capacity of arid and semi-arid ecosystems. Because climate crisis such drought may be the important factors of variability of landscapes in Sahel. For long time, pastoralists have been considered as marginal and primitive. This conduced to a very wrong evaluation of their vulnerability and pastoral techniques. The estimation of access to market and availability of grain stock did not show the variation in decision and the adaptation of pastoralists in difficult environment. The choice to off-take live animals or the decision to modify livestock species are not usually the indicators of crisis. Pastoralists sell their animals to respond to their usually expenses for food security or for the anticipation to a coming stress. In Niger, the catastrophic hunger crisis in 2004/2005 many pastoral families were without assistance. The local authorities did not register them in their current region of camping (Ancey et al., 2009). The local authorities have failed to the rapid alert because their indicators were very fixed and did not integrate all factors of pastoral life variability. The indicators integrated to SIPSA (Ancey et al., 2009) should be used efficiently to predict crisis and for rapid alert response in case they occur in Sahel West Africa.
Different governments should implement clear pastoral policies as one set in Mauritania, to enhance pastoral incertitude and exposure to permanent risks. These policies should integrate all factors of vulnerability in the situation where resource use conflict between farmers and pastoralists is widespread in West Africa sub-region (Shettima and Tar, 2008). However, the UNDP indicators for human poverty and human development will always classified the pastoral society as the poorest. The efforts in investment and rural development programme are needed to strengthen the pastoral activity and to offer good basic infrastructure for health and education. The survey should also be done to evaluate the rate of sedentary pastoralists. These indicators can show the difficult to recovery after a loss of animals during a catastrophe. West Africa countries should create a recovery fund to help pastoralists in reconstitution of herds.
The indicators for pastoral systems impact on the environment are very complex and multicriterial. The integration of ecologic, social, economic and politics factors in one evaluation tools should enhance the assessment of dynamics and changes of pastoral landscape in Sahel West Africa. Simple’s indicators of state should conduce to hasty and wrong decisions. The evaluation methodology of pastoral activity should aggregate and integrate different indicators, because the interactions between pastoral life style and the ecosystems are very strong. Than considering pastoral system as a marginal and primitive sector, West Africa countries should elaborate sustainable rural development policy to improve pastoral life. The constraint of ambiguity in practice of pastoral code and regulations can be resolved. Pastoralism can be a more efficient and sustainable land use system in Sahel zone. Pastoralists are the important operators in livestock production chain. Ignorance of their existence and role in production chain should stay a gap for livestock development. The government should implement the pastoral policies to improve their security and livelihoods. The local knowledge, in term of risks management, mobility, and animal’s off-take, use of rangelands and water resources and mutual aid should be integrated in pastoral code.
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