Monitoring for threshold-dependent decisions

Management decisions are threshold-dependent if actions or determinations change when monitoring data indicate that a resource crossed a specified value (e.g., reference vs impaired conditions). In this chapter, we review the literature on monitoring for threshold-dependent decisions and illustrate how uncertainty and prior knowledge about resource condition may affect such decision thresholds. A critical consideration is whether monitoring is linked to specific management actions and models are available to predict the consequences of those actions on the resource condition. This consideration leads to a split between two different management and monitoring approaches; adaptive management with targeted monitoring or sequential evaluation of resource condition with surveillance monitoring. We compare and contrast these two types of monitoring with regard to threshold concepts, objectives, use of models, and incorporation of uncertainty. Both types of monitoring are being applied to natural resource management, and we cannot conceive of a time when all monitoring will be of only one type. The best strategy, in our view, is to be familiar with when and how to apply both.