Impacts of Grazing

Gary Jones

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Published: August 19, 2002

Ludwig et al. (2000) analyze a prairie/forest grazing system to demonstrate the concepts of stability and resilience. Although this exercise may provide a useful example of the concept of resilience, there are problems with the specific subject chosen for analysis. The scenario involves competition between grasses and woody vegetation in a semiarid environment under grazing pressure and cites Walker et al. (1981) as the source of the system description. Based on those assumptions, a model is built.

The idea that complex systems that interact in complex ways can be usefully modeled by a small number of factors is central to the approach taken by the Resilience Alliance. Conventional policy approaches ignore complexity and develop simplistic "poke-and-hope" interventions that have had poor results. The grazing competition model described in this article indicates a weakness in the Resilience Alliance approach and casts doubt on the idea that complex systems can be usefully modeled by a small number of factors. The selection of factors and the definition of their interactions must be quite correct and sufficiently complete if the model is to be useful. One-dimensional frameworks and frameworks of low dimensionality have not yet been demonstrated to be useful for highly complex natural systems. The fact that they only approximate systems behavior certainly poses some difficulties, but their failure to identify, measure, and model all important dimensions is often a more severe problem.

The grazing competition model contains a central error and is so incompletely described that it is not a true reflection of the system; consequently, its conclusions are flawed. The model assumes that grazing grasses harms them and that this would favor trees. Over time, the model predicts that trees would increase at the expense of grasses.

On the contrary, grazing generally favors grasses, not trees. Tree seedlings are eaten or trampled, so that the forest cannot regenerate. When the old trees die, none take their place. In forests that are grazed, managers plant seedlings in the shelter of rocks or downed trees where grazers are less likely to penetrate. Sometimes noxious shrubs such as greasewood, which few grazers consume in large quantities, can invade a sward, but even these undesirables are best controlled by managed grazing.

More importantly, grazing improves grasses, especially in the semiarid environments this article mentions. Ruminant/sward grazing systems are complex. The animals and grasses coevolved, adapted to one another. The animals, grasses, and a host of soil species ranging from arthropods to worms and bacteria to beetles interact in ways beneficial to each other. These interactions should not really be described as competition. Yes, the grasses get eaten, but what this does is to keep the grass in a youthful, vegetative state for a while longer before it goes to seed. Total biomass production, carbon drawdown, and soil fertility improve. The ruminant pays for its food with urine, dung, and gardening labor as its hooves help break down surface litter so that it can be reused. A grazed sward produces more biomass, more quickly, than an ungrazed sward. Grazing accelerates the virtuous circles of the carbon and nitrogen cycles. See the writings of Wes Jackson, Richard Manning, Andre Voison, and others over the past 100 years for a better understanding of grazing, grasses, and forests. A sward can be overgrazed and damaged just as any system can be overpopulated and exhausted, but modeling such a system and presenting it as the general case is misleading.

I'm fascinated with the idea of trying to account for the interactions of ecosystems, economies, and societies as a way of achieving a better understanding of systems than more narrowly focused, single-discipline approaches are capable of producing. I realize that we don't know enough about these systems yet to do effective modeling. It concerns me that the case selected to demonstrate stability and resilience is not just incomplete but has errors in the selection and measurement of important system attributes. It provides poor insights into complex systems, yet feeds into decisions about economic and social policies. Including practitioners in analysis and model definition might help. Researchers sometimes make rookie mistakes and stumble on issues that many practitioners understand well.

Grazing systems are an ideal subject for the Resilience Alliance to model because they are so complex and have such broad environmental, economic, and social impacts. A useful scenario to explore might be to examine the effects of varying land use in the Great Plains between agricultural use, e.g., growing grains, and pastoral use, e.g., grazing large ruminants. There would be fascinating ecological effects, economic impacts, and social repercussions beyond the local communities. For example, besides being a food, grain is a modern weapon, a political tool with international scope. Growing it is highly regulated and subsidized. It is the foundation of modern industrial agriculture and the main support of civilization. Tinkering with grain makes the whole world tremble. Grazing and meat consumption are widely misunderstood, and there is a lot of misinformation at all levels of society and government.

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Ludwig, D., B. Walker, and C. S. Holling. 1997. Sustainability, stability, and resilience. Conservation Ecology 1(1): 7. [online] URL: http://www.consecol.org/Journal/vol1/iss1/art7.

Walker, B. H., D. Ludwig, C. S. Holling, and R. M. Peterman. 1981. Stability of semiarid savanna grazing systems. Journal of Ecology 69:473-498.