Illius, A.W., Derry, J.F., and Gordon, I.J. (1998) Evaluation of strategies for tracking climatic variation in semi-arid grazing systems. Agricultural Systems, 57 (3). pp. 381-398.

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Abstract

Ways of 'tracking' environmental fluctuations could be of value in limiting drought-induced mortality and increasing output. We examined a range of tracking policies, designed to tackle climatic variation, using a simulation model of a semi-arid grazing system. These compared annual sales designed to limit stocking rate, pre-emptive sales triggered by insufficient rainfall, and variable sales and stocking rate regimes determined by the current season's rainfall. Although the flexible stocking strategies did reduce mortality, losses, compared with fixed stocking, they did not increase average annual sales. The main reasons for this are that major losses of stock are associated less with I-year than with a-year droughts, which are difficult to track, and that destocking can be really effective only if the productive potential of the herd can be re-established more rapidly than is possible from depleted herd resources. Tracking policies did have a considerable advantage in terms of reduced inter-annual variability of sales, which would be of economic benefit to the commercial livestock sector. For subsistence pastoralists, the traditional policies of maintaining the maximum number of breeding stock, and of hoping that most of them will survive drought, may be as close as 'opportunistic' management can get to dealing with drought.

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