The Role of Small Ruminants in Arid Zone Environments: A Review of Research Perspectives

This article provides an overview on small ruminant-environment relations in the arid zones world-wide. We review small ruminant-environment relations under extensive, intensive and very intensive land use systems. The extensive system is common in traditional pastoral production, the intensive in commercial ranching and very intensive in crop-livestock systems. The role of small ruminants in plant community dynamics and productivity of the arid zones under these systems of production is a matter of considerable controversy. Traditionally, small ruminants have been considered to have negative effects on the environment. These views grew out of equilibrium grazing models (i.e., succession, carrying capacity) that associate stocking rates with land degradation. Alternatively, non-equilibrium grazing models (i.e., state-and-transition, rangeland health, thresholds and climate-plant-herbivore interaction) assert that unpredictable climatic events exert a greater influence on the dynamics of arid zone rangelands than do stocking rates. Here, we review extensive evidence to show that equilibrium grazing models heavily influenced grazing studies that linked small ruminants to land degradation in the arid zone. The majority of the short-term studies reviewed failed to separate the effects of climatic variability from those of grazing. By contrast, the long-term grazing studies (over 5 years) consistently revealed that fluctuating climatic conditions controlled production and vegetation cover in the arid zones (i.e., in accordance with non-equilibrium grazing models). Moreover, long-term studies documented that small ruminants promoted ecosystem stability by: I) controlling weeds, 2) constraining bush encroachment; and 3) reducing the risk of fires. Furthermore, small ruminants contribute to ecosystem functioning by mediating the distribution of seeds and soil nutrients. Results from long-term grazing experiments on stocking rates are therefore not in agreement with the preconceived negative role of small ruminants in the arid zones. Thus, claims of land degradation by small ruminants that are based on short-term fluctuations in vegetation cover, species composition, species richness and bare soil, and bush cover that do not account for rainfall variability are of highly questionable merit. In the future, research should be undertaken with a long-term perspective, and should incorporate elements of opportunism (as in non-equilibrium . grazing models), which, we suggest, will be necessary to capture the spatial and temporal variability of grazing resources in the arid zones. In addition, research in the arid zones should apply non-equilibrium models to properly interpret effects of unpredictable events, such as rainfall, on small ruminant production and their relationship to the environment. The article discusses the implications of small ruminant-environmental research for improving research technology to meet future challenges in the arid zones world-wide.