Johan T. du Toit and Nathalie Pettorelli
Rewilding means different things to different people but in applied ecology it is now broadly agreed that the concept means reorganizing, retooling, or regenerating wildness in a degraded ecosystem. Contrary to what many seem to think, rewilding is different from restoring, which by common definition means returning something to its former condition, as with an historic artwork, classic car, or desired landscape. If that is not possible for a disturbed ecosystem in an irreversibly changed environment, then rewilding is the adaptive tactic for regaining and maintaining functionality, perhaps with introduced components. Rewilding is a novel and developing approach that yet attracts controversy because of its inherent unpredictability and emphasis on function over species composition.
It is probably just fine for people in public discussions to talk about rewilding as the process of bringing some wildness back to an area, whether rural or urban, in a way that conflates rewilding with restoration. Nobody really cares about semantics in such discussions but in conservation science it is a different matter - any stand-alone scientific concept needs a clear definition and has to fit within a coherent conceptual framework. Happily, a conceptual framework for rewilding might just exist already in the form of the adaptive cycle, conceived by Buzz Holling and his colleagues from the Resilience Alliance.
Rewilding and restoration draw from different loops of the adaptive cycle. Adapted from Holling & Gunderson (2002).
Ecosystems are complex and dynamic, continually changing and adapting through time (Figure 1). Following a major disturbance, ecosystems generally recover with species reassembling and biomass growing (r phase, lower left panel). Newly available resources become exploited with succession leading to an increasingly connected system with more potential for niches to be occupied. This leads to the accumulation and conservation of resources in a climax state (K phase, upper right panel), with the transition from exploitation to conservation being referred to as the ‘foreloop’ of the cycle.
Then with the next fire, hurricane, drought, outbreak, or over-harvest, the ecosystem releases its potential and connectedness (omega phase, lower right panel), and cycles back into the alpha phase (upper left panel) of reorganization by way of the ‘backloop’. This allows a new assemblage of species to begin exploiting freed resources while developing along a new trajectory governed by new conditions. Restoration (green arrow) is concerned with fast tracking the foreloop and shortcutting the backloop, to return the system to its former condition of high connectedness as soon as possible after a disturbance. In contrast, rewilding (red arrows) draws from the backloop, facilitating reorganization so that the system can adapt to changed conditions, obviating the need for continual management.
Reorganization can lead to two different outcomes, namely (i) a change in composition and/or structure that doesn’t affect the overall nature of the ecosystem and fosters resilience (red arrow to the right); or (ii) a transformation from the historic ecosystem to a novel one (red arrow to the left). The latter is characteristic of situations where environmental conditions change so significantly that a regime shift is inevitable. In these situations, managers can either take a ‘watch-and-see’ approach (passive rewilding) as a novel ecosystem develops on its own, or they can intervene with species introductions and/or engineering works (active rewilding) to generate a novel ecosystem that can sustain the provision of ecosystem services under projected environmental conditions.
Rewilding can operate at multiple levels from genes to ecosystems, and managers can facilitate rewilding in many ways from reintroductions and translocations to mechanical engineering projects. It is a concept that embraces new opportunities and provides a way forward for ecosystems where restoration is not an option. Because rewilding focuses on processes and functions, the approach requires thinking outside the box and stimulates managers to consider why a functional type of organism is important rather than which species should or should not be present. Interestingly, this type of thinking is also developing in theoretical ecology, with a growing number of studies highlighting the importance of functional trait distribution for ecosystem processes and ecosystem services delivery.
Admittedly, rewilding pushes the boundaries of our comfort zone by forcing us to think more like a mechanic than an art restorer, thereby highlighting our knowledge gaps. But the concept also challenges us to recognize the dynamic nature of biological systems, and factor in change instead of fearing it. Ultimately, the rise of the rewilding concept is a sign that new approaches are urgently needed to conserve biodiversity and maintain ecosystem services under increasingly unpredictable global conditions, as traditional approaches on their own are demonstrably unfit for the challenges ahead.
Learn more about rewilding at our science and conservation event Rewilding in a changing climate on 11 December. This event is free and open to all.
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