Introduction to grassland ecosystems
Grasslands cover a very large portion of the earth’s surface and are important as a feed source for livestock, as a habitat for wildlife, for environmental protection and for the in-situ conservation of plant genetic resources. In both developed and developing countries, many millions of livestock farmers, ranchers and pastoralists depend on grasslands and conserved products such as hay and silage and on a range of fodder crops for their livelihoods. Rapid increases in human and livestock populations have contributed to increased pressures on the world’s grasslands, particularly in arid and semi-arid environments. The Oxford Dictionary of Plant Sciences (Allaby, 1998) gives a succinct definition: “Grassland occurs where there is sufficient moisture for grass growth, but where environmental conditions, both climatic and anthropogenic, prevent tree growth. Its occurrence, therefore, correlates with a rainfall intensity between that of desert and forest and is extended by grazing and/or fire to form a plagioclimax in many areas that were previously forested.”
Grasslands are among the largest ecosystems in the world; their area is estimated at 52.5 million square kilometres, or 40.5 percent of the terrestrial area excluding Greenland and Antarctica (World Resources Institute, 2000, based on IGBP data). In contrast, 13.8 percent of the global land area (excl. Greenland and Antarctica) is woody savannah and savannah; 12.7 percent is open and closed shrub; 8.3 percent is non-woody grassland; and 5.7 percent is tundra. In its narrow sense, “grassland” may be defined as ground covered by vegetation dominated by grasses, with little or no tree cover; UNESCO defines grassland as “land covered with herbaceous plants with less than 10 percent tree and shrub cover” and wooded grassland as 10–40 percent tree and shrub cover (White, 1983).
No grassland is entirely natural, and there are many degrees of interference: fire, whether spontaneous or lit by man, has influenced, and continues to influence, large areas; and grazing by livestock and, in some continents, by large herds of wild herbivores. More invasive interventions have been clearing of woody vegetation either to give better grazing or originally for cropping; subdivision with or without fencing ; provision of water points to extend the grazing area or season; and various “improvement ” techniques such as oversowing with pasture grass and legume seeds – with or without surface scarification and fertilizer . In the early days of FAO, Semple (1956) summarized much of the available techniques and problems, and most are relevant today, although some technologies have progressed in detail. In general, grassland is said to be natural if it is not the result of full ploughing and sowing – the composition of much old sown pasture has, of course, little to do with the seed mixture used at its establishment.
The better-watered parts of many of the world’s great grassland zones have been developed for arable farming, notably in the North American Prairie, the South American Pampas, and the East European Steppe, and grazing is now often relegated to the more marginal lands, unfit for cropping, where the population is often totally dependent on livestock for its livelihood. In Africa also there is little extensive grassland uncultivated in regions where the rainfall permits the production of even meagre subsistence crops. The effect of developing the best land for crops has several negative effects on the use of the remaining land for grazing, including obstructing traditional migration routes in zones of transhumance and denying access to water points.
Pasture and forage crops
Extensive grazing is usually the exploitation of managed natural ecosystems on which human activities may have had a considerable impact to facilitate or improve livestock production; it is a land use, not a specific crop, and must, for example, compete with crops, wildlife, forestry and recreation. The choice of use is not fixed and depends on economic factors as well as soil and climate. It is usually on land unsuitable for intensive cultivation because of topography, poor soil or a short growing season – the season may be limited by moisture availability or temperature. Exploitation by the grazing animal is, in many countries, the principal practical method of exploiting the natural vegetation of arid, stony, flooded, montane or remote areas. It follows, therefore, that all discussion of grassland must be in the context of animal production and of the human communities that gain their livelihood thereby (Riveros, 1993).
Sown pasture is important within commercial arable farming systems, and, since it competes with other crops for land and inputs, must be economically viable compared with other crops at the farm -system level. In well -watered areas it may replace natural grassland, often in association with crop production. Sown pastures are usually most productive in their early years and yields fall off thereafter; to remain productive they require careful management and inputs, with or without periodic resowing; they usually also need fencing and water reticulation. Since grazing requires fairly large, enclosed areas to be managed effectively, sown pasture is not really suited to smallholder farms.
Sown fodder, often irrigated in semi -arid areas, can provide conserved fodder for winter use, and examples are given in the chapters on North America, Patagonia, Russia and the Campos. Fodder growing is traditional in some smallholder areas, but, unlike sown pasture , fodder can be used on any size of farm , not only large ones, whether for use green or conserved; how it has become very important economically in the Pakistan Punjab is described by Dost (2004). Hay from natural meadows has been used by herders for a very long time, but traditional pastoralists do not usually sow fodder; Wang (2003) describes an interesting scheme in the Altai region of Xinjiang in China , wherein Kazakh herders produce alfalfa (Medicago sativa ) hay for winter feed on irrigated lowlands while maintaining their spring to autumn transhumant migration.
Crop residues, especially straws and stovers are very important as livestock feed in both commercial and traditional systems; in commercial farming they are usually part of the roughage ration and supplemented with other fodders and concentrates; in traditional subsistence systems they may be the main feed when grazing is not available. In the irrigated lands of southern Asia, crop residues are often the main feed of large ruminants year-round. Residues are not discussed in detail in most of the studies, but their conservation and use is described in a recent FAO Grassland Group publication (Suttie, 2000). In some extensive grazing systems with adjacent cropping zones, crop residues may also figure as lean-season feed. Lean seasons vary: in some areas it is winter; in tropical areas it is the dry season; and in Mediterranean zones it is the hot, dry summer. It is, of course, much more important in agricultural and mixed farming areas. Crop residues and stubbles are important in West Africa n transhumance systems and there is a complementarity between cropping and stock rearing communities: herders move north into the desert fringe during the rains (and the season when the crops are on the ground) and move back to the agricultural areas after harvest, in the dry season; traditionally the farmers did not keep livestock.
Pastures are the basic feed resources for livestock worldwide and in humid areas mixed farming systems supply over 90% of the milk, 70% of sheep and goat meat, and 35% of beef.
The development of integrated systems based on annual crops in association and rotation with pastures and forages for livestock, responds to a variety of needs to:
• intensify crop production;
• increase profitability and precision of inputs;
• increase farmers’ security;
• preserve natural resources and the environment.
Generally farmers invest more labour and inputs to produce a crop (such as rice, cotton, soybean, maize, rubber and coconut) than to produce forage for livestock. However, the production of pastures is as important as the production of crops to increase farm income and security, to improve biodiversity and environmental benefits, to improve efficiency of fertilizers and zero tillage. Pastures are the basic feed resources for livestock worldwide and in humid areas mixed farming systems supply over 90% of the milk, 70% of sheep and goat meat, and 35% of beef. The development of integrated systems based on annual crops in association and rotation with pastures and forages for livestock, responds to a variety of needs to:
FAO promotes information sharing and training of scientists, technicians, farmers and policy makers on the biology, the technologies and best practices to enhance the integration between crops and pasture production in different ecologies.
Grazing systems can be roughly divided into two main types – commercial and traditional, with the traditional type often mainly aimed at subsistence. Commercial grazing of natural pasture is very often large-scale and commonly involves a single species, usually beef cattle or sheep, which would mainly be for wool production. Some of the largest areas of extensive commercial grazing developed in the nineteenth century on land which had not previously been heavily grazed by ruminants; these grazing industries were mainly developed by immigrant communities in the Americas and Australasia, and to a much less degree in southern and eastern Africa . Traditional livestock production systems are very varied according to climate and the overall farming systems of the area. They also use a wider range of livestock, since buffaloes, asses, goats, yak and camels are predominantly raised in the traditional sector.
In traditional farming systems livestock are often mainly kept for subsistence and savings, and are frequently multi- purpose, providing meat, milk, draught, fibres and frequently fuel in the form of dung-cakes. In many cultures the number of livestock is associated with social standing. Many traditional systems are sedentary, and these are usually agropastoral, combining crop production with livestock that can utilize crop residues and by-products and make use of land unsuitable for crops. Extensive grasslands, however, are frequently exploited by mobile systems, transhumant or nomadic, where herds move between grazing areas according to season; some move according to temperature, others follow feed availability.
The herbaceous layer of grazing lands is usually, but not always, grasses; several other plant types cover large grazed areas. Cyperaceae, especially Kobresia spp., dominate many of the better-watered, hard-grazed yak pastures, especially those of the alpine meadow type. Halophytes, notably Chenopodiaceae, both herbaceous and shrubby, are important on alkaline and saline soils in many arid and semi -arid grazing lands. In tundra, lichens, especially Cladonia rangifer, and mosses provide reindeer feed. Sub-shrubs are important: various species of Artemisia are important in steppic regions of the old world from North Africa to the northern limit of the steppe, and also occur in North America. Ericaceous sub-shrubs (species of Calluna, Erica and Vaccinium ) are very important grazing for sheep and deer on UK moorland. Browse is frequently mentioned as a significant feed source, often consumed in the lean season and in some cases fruits are also eaten. Tree fodder is especially important in tropical and sub-tropical situations with alternating wet and dry season s and is discussed in the chapters on Africa and Australia (where it may be referred to as “top feed”). Various mixed shrub formations (garrigue, maquis) are grazed in the Mediterranean zone. Trees and shrubs, notably Salix spp., are also winter weed in some cold areas.
Extensive grasslands have multiple uses in addition to being a very important source of livestock feed and of livelihoods for stock raisers and herders. Most grasslands are important catchment areas and the management of their vegetation is of primordial importance for the water resources of downstream lands; mismanagement of the grazing not only damages the pasture, but, since it increases erosion and run-off, can cause serious damage to agricultural land and infrastructure lower in the catchment and cause siltation of irrigation systems and reservoirs. The main benefits of good catchment management mainly accrue to communities outside the grasslands, but the maintenance efforts have to be made by herders or ranchers. These grasslands are major reserves of biodiversity, providing important wildlife habitat and in situ conservation of genetic resources. In some regions, grasslands are important for tourism and leisure, and may have sites of religious significance; in other areas, wild foods, medicines and other useful products are collected. Grasslands are a very large carbon sink at world level. Minahi et al. (1993) state that they are almost as important as forests in the recycling of greenhouse gasses and that soil organic matter under grassland is of the same magnitude as in tree biomass; the carbon storage capacity under grassland can be increased by avoiding tillage (see section on Conservation Agriculture).
The terms “nomadism” and “transhumance” are sometimes used indiscriminately when applied to mobile livestock production systems. Transhumance describes those pastoral systems where people with their animals moved between two distinct seasonal pasture areas, usually at considerable distance or altitude from each other. Nomadism is used for pastoral groups that have no fixed base, but follow erratic rain storms. Great grazing lands still exist, however. Among the most important are the steppes that stretch from Mongolia and northern China to Europe; the Tibet -Qinghai Plateau and the adjacent mountain grazing of the Himalaya -Hindu Kush; the North American prairies; in South America – the Pampas , the Chaco, Campos, Llanos and Cerrados pastures, the cold lands of Patagonia and the Altiplanos; the Australian grasslands; in the Mediterranean Region and western Asia there are large areas of semi -arid grazed land; south of the Sahara there are the vast Sahelian and Sudano-Sahelian zones, as well as most of the eastern part of Africa from the Horn to the Cape.