Characteristics of grazing land: general

Editor's note: Text extracted from D211-2.1

According to Food and Agriculture Organisation of the United Nations FAO (1996) about one-quarter of the world's total land area is used for grazing livestock and one fifth of the world's arable land is used for growing cereals for livestock feed. Together this makes livestock production one of the largest land uses in the world. Grazing ecosystems provide both market services, such as livestock production and genetic resources, and non-market services, such as landscape, recreation and culture. The importance of these non-market services is often higher than the grazing services, as for example reported by Fleischer and Sternberg  (2006) in Israel, where  urban populations value the green landscape of rangelands in the Mediterranean climate region and are willing to pay for conserving it in light of the expected increasing aridity conditions in this region.

Rangeland ecosystems are complex systems composed of different subsystems that interact with each other, resulting in patterns and processes that cannot be understood by analysis of their individual parts alone. Rangeland systems involve interactions between ecological, economic and social forces in a non-linear way. Fundamental processes of land degradation and desertification in grazing land are driven by positive feedbacks (causing regime shifts). The effect of domestic grazing has variable effects on ecosystem structure and processes, which may depend on the long evolutionary histories of grazing (Milchunas et al. 1988; Perevolotsky and Seligman 1998; Adler et al. 2004; Adler et al. 2005). In ecosystems with a long evolutionary history of grazing, vegetation is adapted to large herbivores and consequently, livestock grazing may even be necessary to maintain ecosystem biodiversity (McNaughton 1979; Naveh and Wittaker 1979; Collins 1987). Only under permanent overgrazing were traditional herd management practices believed to be environmentally destructive (Hary et al. 1996). There is evidence of irreversible land degradation in systems that evolved under high grazing pressure, such as African deserts and savannas (Milton et al. 1994; Illius and O'Connor 1999; Tobler et al. 2003) or Argentinean rangelands (Cingolani et al. 2005; Cingolani et al. 2008). Rangeland livestock systems are also considered to degrade when they are affected by climatic variability, especially in arid and semi-arid areas. Climatic variability is the largest cause of poverty in pastoral societies (Ellis et al. 1993; Aidoud et al. 1998; Koukoura et al. 1998; Ward et al. 1998).

Livestock do not use the landscape homogeneously, but have preferred areas, which results in uneven distribution of animal impact. Landscape heterogeneity increases as grazing intensity increases, resulting in heavier impacts on preferred areas. In traditionally managed grazing systems, mobile pastoralism provides a way to respond to variations in intra- and inter-annual climatic fluctuations (Fryxell and Sinclair 1988)  and prevent desertification by overgrazing (Homann et al. 2008). In areas where traditional grazing is not the case, as in USA rangeland ecosystems for example, rotational grazing has been proposed as a remedy for deterioration due to patch grazing (Kirkman and Moore 1995; Teague and Dowhower 2003). This practice is also used in Australian arid rangelands (Westoby et al. 1989). It is argued that pastoralist coping strategies to deal with climate variability, land tenure and access issues are more important than stocking rates in preventing land degradation (Derry and Boone 2010).  These findings indicate that application of the carrying capacity concept is not capable of preventing desertification in extensive pasture, even under equilibrium conditions. The spatial dynamics of the interaction between animal behaviour and vegetation are non-linear and the distribution of grazing pressure is more important than total grazing pressure, which has only a limited influence on degradation (Okayasu et al. 2010). Therefore, explicit management of the spatial distribution of animals is essential to prevent land degradation and desertification in extensively grazed rangelands. Recently, researchers have shown in different parts of the world that livestock have little impact on forage resources (Fernandez-Gimenez and Allen-Diaz 1999; Sullivan and Rohde 2002; Lind et al. 2003) and so are not considered the main cause of degradation of rangeland and consequently desertification (Dean et al. 1995; Sefe et al. 1996; Okayasu et al. 2010). This is explained because high levels of climatic variability with peak droughts cause crashes in the animal populations, causing higher mortality rates in livestock and as a result overgrazing is halted before the desertification process is triggered (Derry and Boone 2010).  This is only the case when animals are not provided with supplementary food during periods of food shortage. In addition, herbivores and herds tend to respond opportunistically to climate changes in rangelands (Ellis et al. 1993). They exploit the vegetation during production peaks and move to other areas when drought arrives, when there is opportunity for doing so.

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