Resilience and thresholds in river ecosystems

Abstract

This Waterlines report is part of a series of papers commissioned on issues relating to Australian aquatic ecosystems. These Waterlines reports will contribute to improved environmental water management by stimulating discussion, synthesising current thinking, identifying knowledge gaps, and highlighting areas that warrant further investigation. With increasing anthropogenic pressures on river ecosystems, the way that rivers are managed is critical for the maintenance and improvement of human wellbeing. Like much of the world, Australian practices of terrestrial and aquatic ecosystem management have relied on notions of a uniform equilibrium state, where the focus has been on increasing or optimising efficiency and performance in order to deliver defined benefits, including supply or sustainability (Hillman et al. 2005; Walker and Salt 2006). Yet Australian river ecosystems are under pressure and continue to degrade under existing management practices. This is not surprising. Ecosystems are moving targets, which are characterised by episodic change, patchiness, variability, multiple scales of operation, and multiple stable states in both the social and biophysical domains (Gunderson and Holling 2002). Time and time again, ecosystems managed for some type of equilibrium carrying capacity have been thwarted by surprise events, changes in thresholds, and market failures (Carpenter and Folke 2006). Time and time again it has been shown that optimising efficiency to deliver a defined benefit does not lead to sustainability, but rather to collapse (Walker and Salt 2006). New ideas are required to improve the management of Australian river ecosystems. One such idea - resilience thinking - provides an umbrella under which to consider the future management of river ecosystems. Resilience is the amount of change a system can undergo (its capacity to absorb disturbance) and remain within the same regime that essentially retains the same function, structure and feedbacks (Walker and Salt 2006). Resilience thinking seeks to determine how societies, economies and ecosystems can be managed to confer resilience: that is, how to maintain the capacity of a system to absorb disturbance without changing to a different state. The aims of this project are to: 1. review the concepts of resilience and thresholds as they apply in river ecosystems 2. identify the components of a framework to assist planners in managing the resilience of river ecosystems.