Managing environmental water for ecological resilience

Ecological systems are constantly disturbed by natural and human-induced changes to the environment. Ecological resilience is important to understand when managing environmental water flows.

Different types of resilience

Resilience can be defined in different ways depending on the context you are working within and the angle of approach. The ecological resilience definition is the main focus of our work in environmental flow management, however, it is important to understand that there are multiple definitions and uses of the term:

• Social resilience: the ability to absorb change and maintain key social connections and structures.
• Economic resilience: the ability to adapt to change to create an improved state.
• Ecological resilience: the ability to resist change and rebound to its previous state.

What is ecological resilience?

In terms of ecological resilience, it refers to an ecosystems’ stability and capability of tolerating disturbance and restoring itself. Ecological resilience has two components:

1. The time required for an ecosystem to return to an equilibrium following a disturbance – its ability to recover and respond
2. The capacity of a system to absorb disturbance and reorganise while undergoing change, and still retain the same function, structure, identity and feedbacks – its ability to resist change

Image: Resistance and resilience in ecological systems

A significant part of ecological resilience is resistance, which is the ability to resist change. Some species or ecosystems, such as Red gums, are very resistant to changes but have slow resilience to restore itself during better conditions.  In contrast, other species like native frogs, have low resistance to ecological changes but high resilience. This means frog populations decline rapidly in dry times but can recover quickly when water is back in the landscape. Red gums, however, are resistant to degrading conditions but require more time to recover and develop resilience.

Images: Comparison between the resistance and resilience of frogs and red gums after environmental flows

This has important implications for the way we think about water management.

Why does resilience matter?

1. It determines the magnitude and timing of ecological responses to management interventions such as environmental watering
2. It guides us in what trajectories of change we can expect in highly disturbed and highly managed ecosystems subject to ongoing change.

Managing for resilience

Different aspects of an ecosystem determine its level of resilience and resistance:

1. The traits of the species involved.
2. Dispersal and connectivity to habitats in good condition – for example connecting refugia for specific animals.
3. Food web structure – we can manage flows for different parts of the food web in the specific ecosystem.
4. The presence of other stressors – such as climate change, land-use change, invasive species.

Implications for water flow management

Water managers need to understand what they are managing for and the different components of their ecosystem. Understanding which components are naturally resilient will enable them to appropriately provide water to the river system. Some parts of the landscape are critical to improving the overall resilience of species, such as refugia locations.

Water managers need to also consider which components of their ecosystem are resistant to change, or are more resilient during recovery. Naturally resistant parts of the landscape need to be watered early to maintain their population, whereas naturally resilient components need water flows when there is high rainfall and flow.

It is also important for water managers to consider how long the resilience of a species can last. Even though its ecological condition may naturally fall during dry periods, there may be a point where it has fallen too low for water flows to build it back up.

Other non-water management factors may be affecting resilience. This can limit the response that we can see from environmental water. This also demonstrates the importance of interdisciplinary resilience thinking across social, economic and ecological sectors.