The Importance of ‘moving targets’ in assessing what is physically achievable and what we seek to achieve in river restoration practice

The shifting baseline syndrome asserts that what we measure against in environmental assessments is dependent upon the condition/state of ecosystems at a particular timeframe of reference. Although initially conceived in relation to measures of biodiversity, here we show how geomorphic considerations can use this concept to frame shifting terms of reference that define what is realistically achievable in restoration activities that address concerns for the physical structure and function of river systems. We demonstrate the use of the river evolution diagram as a generic tool that relates the historical range of variability to notions of naturalness, showing how understandings of evolutionary trajectories can be used to determine the best achievable condition for any given system. Given multiple alternative pathways of adjustment, and the potential for threshold-induced river change, restoration activities are most appropriately framed as ‘moving targets’. Adaptive (flexible) management frameworks are required to communicate and facilitate adjustments towards uncertain futures in which surprises are inevitable.