Economic implications of maintaining rangeland ecosystem health in a semi-arid savanna
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A simulation model was used to determine the ecological and economic consequences of managing stocking rate on semi-arid savanna rangeland continuously stocked with livestock to achieve the alternate management goals: (1) maintaining current range condition, (2) maximizing profit, or (3) improving range condition over a 30-year time frame. We developed values for end of the year herbaceous standing crop and utilization required to attain these management goals for rangeland in poor to excellent condition. Based on extensive field research conducted in this region over 5 decades, range condition in this model is programmed to decline in response to three factors: excessive grazing pressure, below average precipitation, and an increase in woody plants. Earning capacity is four times higher for range in excellent condition than that in poor condition. For all initial range condition (RC) values, simulated stocking rates that maintained RC resulted in simulated mean weaning weights 93-94% of maximum. Maximum short-term and long-term profit is attained at higher stocking rates than would maintain long-term range condition and at much higher levels than would increase range condition levels. When stocked for maximum profit, individual animal performance was 90% of maximum. The model predicts that low stocking rates allow range condition to improve. At these recovery stocking rates, total 30-year profits were found to be 78%-87% of the stocking rates that would maintain range condition, and only 67%-75% of stocking rates that would maximize profit. Predictions of the end of year standing crop to maintain range condition were in broad agreement with the 1000kg ha- 1 advised for this region. To improve range condition, the model predicts that an end of year standing crop of 1500-2000kg ha- 1 is required, compared to the generally advised level of 1200-1500kg ha- 1. The predicted end of year forage standing crops for the maximum profit goal are well below the advised 800kg ha- 1 threshold required to prevent degradation for all of the initial range conditions that were simulated. To ensure maintenance of range in excellent condition, our results concur with the advised utilization levels of 20-25%. However, for range in poorer than excellent condition, the model predicted much lower utilization levels were needed to maintain or improve range condition. 2008 Elsevier B.V. All rights reserved.
