Setting conservation management thresholds
Monitoring is routinely used by conservation managers to determine the state of the environmental values they are responsible for. That might be the numbers of a threatened species or the health of an ecosystem in a national park. When changes in condition are observed, decisions should be made about whether or not to intervene. It might be that the numbers of the threatened species have dropped to a level where this population requires assistance or the health of the ecosystem deteriorates and needs some form of intervention.
Why set management thresholds?
Management thresholds are changes that ‘trigger’ a manager to do something, to actively intervene in the system they are responsible for. They are a useful tool to inform decision-makers about when undesirable environmental changes require management intervention. Management thresholds are commonly used in natural resource management like fisheries and water quality management, but they are not so common in conservation.
The consequences of not having a threshold to trigger action can be dire. There have been instances where programs have monitored species of conservation value until they became extinct without triggering an adequate or timely intervention (consider the recent extinction of the Christmas Island pipistrelle, see Decision Point #60). Instances such as these highlight the critical need for a proactive form of conservation management, where management thresholds and associated management actions are defined a priori, rather than reacting to unexpected future ecosystem changes.
Management thresholds for the real world
There are existing approaches to setting conservation management thresholds, including identifying thresholds of potential concern, statistical thresholds, and decision thresholds. However, one single approach to setting management thresholds will not be suitable for all contexts, as conservation decisions often involve different circumstances that will require different tools and approaches.
When working with Parks Victoria to improve the management of a Port Phillip Heads Marine National Park, we found ourselves in need of an approach to develop management thresholds that (1) must be set for environmental indicators in the face of multiple competing objectives; (2) need to incorporate scientific understanding and value judgments; and, (3) involve participants in the process with limited modelling experience. In response to these needs we devised a new participatory modelling approach for setting management thresholds that was suitable for this decision context.
The approach we devised follows the steps of structured decision-making, a process that is very useful in supporting multi-objective conservation decision-making (see Decision Point #74 for a range of articles on structured decision-making).
In addition to incorporating scientific knowledge and value judgments into decision-making, structured decision-making promotes the involvement of decision makers, stakeholders, and experts in the decision-making process. Our approach uses a novel combination of modelling techniques to set conservation management thresholds (Figure 1).
Thresholds for a brown alga
In Addison et al, (2015) we describe this participatory modelling approach to set management thresholds, and illustrate its application using a case study where management thresholds were set for an intertidal mat-forming brown alga, Hormosira banksii (Figure 2), in Port Phillip Heads Marine National Park. (The alga is commonly known as Neptune’s necklace.)
Management staff and scientists were involved in a workshop to test the approach, and set management thresholds to address the threat of trampling by visitors to an intertidal rocky reef. Managers were faced with a multi-objective problem, which ultimately involved a trade-off between a fundamental environmental objective, to maintain the condition of intertidal reef communities, with social and economic objectives to ensure management intervention did not detract from the visitor experience and was cost-effective.
A key part of our approach is to define potential future condition states of the primary ecological indicator, referred to as ecological scenarios. In this case we used scenario planning to define scenarios that represent the current condition, and plausible declines in percent cover of Hormosira that may occur under increased threatening processes in the future (Figure 3).
Workshop participants defined the fundamental objectives for the management of the intertidal reef, which were to: maximize rocky intertidal reef communities (represented by the proxy indicator, H. banksii cover), minimize resources spent on management, maximize visitor satisfaction, and maximize visitor numbers to the intertidal reef. They then defined four discrete management alternatives, each made up of a set of individual actions, and estimated the consequence of these alternatives on the objectives for each ecological scenario.
A weighted additive model was used to aggregate participants’ consequence estimates. Model outputs (decision scores) clearly expressed uncertainty (Figure 3), which can be considered by decision-makers and used to inform where to set management thresholds.
There is a critical need for a proactive form of conservation management, where management thresholds and associated management actions are defined a priori, rather than reacting to unexpected future ecosystem changes.
The threshold and ‘preferred’ management strategy will depend on the decision-maker’s risk attitude, and may vary with different decision contexts. In Figure 3 for example, a risk averse decision maker may operate under the status-quo alternative, but set a management threshold at 42% cover to trigger a change to the medium protection management alternative, because it is now the preferred alternative (has the highest lower-bound decision score). This can then inform the range within which the management threshold would be set for the medium protection alternative (between 15 – 42% cover of H. banksii; Figure 4).
The final decision to set a management threshold will reflect a decision makers’ risk tolerance associated with the decision context. A risk-averse decision maker will set a management threshold toward the maximum value of the implementation range, whereas a risk-seeking decision maker may set a management threshold toward the minimum value of the implementation range.
Long-term monitoring data should be regularly evaluated against management thresholds. If a management threshold is breached, the associated management action should be implemented. If a management threshold has not been breached, monitoring should continue under the preferred management. The learn-and-review feedback loops (Figure 1) encourage the continual improvement through clarifying uncertainty associated with model parameters, evaluating the true effectiveness of management interventions, and revising the decision context where necessary.
More info: Prue Addison email@example.com
Note: This research was part of Prue Addison’s PhD at the University of Melbourne. She is now a postdoc at AIMS.
Addison PFE, K de Bie & L Rumpff (2015). Setting conservation management thresholds using a novel participatory modelling approach. Conservation Biology. DOI: 10.1111/cobi.12544. http://onlinelibrary.wiley.com/doi/10.1111/cobi.12544/epdf