A framework for deriving and triggering thresholds for management intervention in uncertain, varying and time-lagged systems

Abstract

Ecosystems are characterised by complexity: high connectivity, the presence of positive and negative feedback loops, non-linear, abrupt and sometimes irreversible changes, delays between cause and effects, and uncertainties in observations, understanding and prediction. ‘Adaptive management’ is the preferred approach for the rational management of such systems. Where the management objective is to allow natural feedbacks and adaptive processes to operate as much as possible – as it is in many areas set aside for biodiversity conservation – a key issue is defining the thresholds that will trigger management intervention. This paper outlines and illustrates a logical process for doing so, taking into account the characteristics of complex, continuously changing ecosystems and the reality of information that is partial and understanding that is always provisional. After identifying a key ecological process that is believed to have an element of irreversibility beyond a certain point, the process has several steps, (1) define an indicator of the system state, (2) set a limit of acceptable change and add a safety margin, (3) project the indicator forward using a model, including uncertainty, (4) note the time when the indicator might transgress the safety-buffered limit and (5) subtract ecosystem and management response times. If the resultant time is at hand, an action is indicated – if not, the action is to continue to monitor the situation and refine the observations and models.<p><strong>Conservation implications:</strong> Ecosystems are characterized by abrupt and sometimes irreversible changes. The challenge that face conservationists and managers are to identify which of these changes are likely to be irreversible and at what levels this will occur. This paper describes a logical process that enable mangers to determine which ecological processes have levels of irreversibility and monitor their status at all times. Once these processes are nearing the levels that are undesirable management actions can be invoked to prevent this from happening.</p><p><strong>How to cite this article:</strong> Scholes, R.J. & Kruger, J.M., 2011, ‘A framework for deriving and triggering thresholds for management intervention in uncertain, varying and time-lagged systems’, <em>Koedoe</em> 53(2), Art. #987, 8 pages. doi:10.4102/koedoe.v53i2.987</p&gt

Best Practice Framework and Principles for Monitoring the Effect of Coastal Development on Marine Mammals

“…Levels of acceptable and unacceptable change along with safety margins for indicators are not only informed by statistical inference and ecological values, but also by social and economic values (Scholes and Kruger, 2011). Accordingly, the limits of change may be set on societal values rather than system thresholds or ecological limits alone (e.g., zero mortality for an iconic species).…”

“…The indicators and triggers selected will be project specific and informed by the species and its conservation status, habitat type, the ecological relationships between species and habitat features, and the type of development and associated activities. In this context an indicator is a measure that can be related to the vital rates or other factor of concern for a community or population (Scholes and Kruger, 2011;Fleishman et al, 2016). Hence, a critical component to consider when selecting indicators and trigger points is the pathway through which measurable effects (e.g., behavioral changes) can influence vital rates (or other factors of concern).…”

“…A trigger point or threshold in this case refers to the levels or values of change that the activity or project is attempting to achieve or avoid (Block et al, 2001). Defined limits of change preferably originate from knowledge of "true system thresholds" (Scholes and Kruger, 2011). It is recommended that these thresholds are re-assessed as part of the design of monitoring programs and feedback mechanisms.…”

“…Uncertainties may arise due to difficulties in predicting the precise boundaries of acceptable limits and these are reflected in the set safety margins of predictions. Scholes and Kruger (2011) noted that the key measure in predictions is not the point at which the threshold is intercepted, but the earliest point at which the change reaches the lower detectable safety margin. At this point, there should be sufficient notification that a threshold is being approached and early preventative measures can be activated (Scholes and Kruger, 2011).…”

“…Outlining categories that define how close thresholds or trigger points are at a given point in the monitoring program can provide a useful approach to inform management actions. Scholes and Kruger (2011) describe a multi-stage warning system that reflects levels of "potential concern" and incorporates system, management and monitoring response intervals. The system integrates levels of uncertainty within safety margins and predicted timescales where a certain impact may occur.…”