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Allowing variance may enlarge the safe operating space for exploited ecosystems.

S. R. Carpenter, W. A. Brock, C. Folke, E. H. van Nes and M. Scheffer (2015). Proceedings of the National Academy of Sciences USA 112:14384-14389.


Variable flows of food, water, or other ecosystem services complicate planning. Management strategies that decrease variability and increase predictabilitymay therefore be preferred. However, actions to decrease variance over short timescales (2–4 y), when applied continuously,may lead to long-termecosystem changes with adverse consequences. We investigated the effects of managing short-term variance in three well-understood models of ecosystem services: lake eutrophication, harvest of a wild population, and yield of domestic herbivores on a rangeland. In all cases, actions to decrease variance can increase the risk of crossing critical ecosystem thresholds, resulting in less desirable ecosystem states. Managing to decrease shortterm variance creates ecosystem fragility by changing the boundaries of safe operating spaces, suppressing information needed for adaptive management, cancelling signals of declining resilience, and removing pressures that may build tolerance of stress. Thus, the management of variance interacts strongly and inseparably with the management of resilience. By allowing for variation, learning, and flexibility while observing change, managers can detect opportunities and problems as they develop while sustaining the capacity to deal with them.

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Keywords: adaptive management, critical transition. ecosystem, resilience, variance

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