Six ‘key principles’ are used here to provide a framework for conceptualizing, defining and measuring ecological restoration, particularly at a time of rapid environmental change.
Principle 1 Ecological restoration practice is based on an appropriate local indigenous reference ecosystem
A fundamental principle of ecological restoration is the identification of an appropriate reference ecosystem to guide project targets and provide a basis for monitoring and assessing outcomes. The reference ecosystem can be an actual site (reference site) or a conceptual model synthesized from numerous reference sites, field indicators and historical and predictive records. It includes local indigenous plants, animals and other biota characteristic of the pre-degradation ecosystem. (For exceptions see Box 1). The reference ecosystem may also include species from neighbouring localities that have recently naturally migrated e.g. due to a changing climate. Where local evidence is lacking, regional information can help inform identification of likely local indigenous ecosystems. Identifying a reference ecosystem involves analysis of the composition (species), structure (complexity and configuration) and function (processes and dynamics) of the ecosystem to be restored on the site. The model should also include descriptions of successional states that may be characteristic of the ecosystem’s decline or recovery.
A reference ecosystem is a model adopted to identify the particular ecosystem that is the target of the restoration project. This involves describing the specific compositional, structural and functional ecosystem attributes requiring reinstatement before the desired outcome (the restored state) can be said to have been achieved.
Australia’s landmass, waterways and marine areas contain many intact or remnant indigenous ecosystems. The site’s pre-degradation ecosystems are used as starting points for identifying restoration targets—taking into account natural variation and acknowledging the fact that ecosystems are dynamic and adapt and evolve over time, including in response to changing environmental conditions. That is, we use existing and recent assemblages, coupled with sound scientific and practical knowledge of current and future environmental conditions, to help identify suitable reference ecosystems. Where irreversible altered topography, hydrology, or climatic conditions have occurred or are predicted; a local indigenous ecosystem more ecologically appropriate to the changed conditions may be used as a guide (see caveats in Box 1). Adopting a reference ecosystem is therefore not an attempt to immobilize an ecosystem at some point in time but to optimise potential for local species to recover and continue to evolve and reassemble over subsequent millennia.
Identifying functional components of a reference ecosystem is important to goal setting; but returning functions also facilitates restoration. That is, recovery is achieved by the processes of growth, reproduction and recruitment of the organisms themselves over time, facilitated by the return of appropriate cycles, flows, productivity levels and specific habitat structures or niches. Monitoring of the recovery process is required to identify whether acceptable trajectories of recovery are likely to result in a self-organizing and functional ecosystem or whether further (or different) interventions are needed to remove barriers to recovery.
Box 1 Reference ecosystems in cases of irreversible environmental change
Many local sites, intact or degraded, are becoming increasingly threatened by human activities and some of these result in effectively irreversible impacts. Reinstating local indigenous ecosystems in cases where irreversible environmental change has occurred requires anticipation and, if necessary, mimicry of natural adaptive processes.
- Irreversible physical (soil and water) and biological changes.In cases where insurmountable environmental change has occurred
to the site and the pre- degradation ecosystem cannot be reinstated, an appropriate solution would be to establish an alternative, locally
occurring ecosystem that would be expected to naturally occur under the changed conditions. (Examples include sites where hydrology has changed
irreversibly from saline to freshwater or vice versa, traditional fire regimes cannot be reinstated, or where erosion has produced a rocky platform).
Examples of conversion.
Whether such activities function as ecological restoration, a complementary restorative activity or simply a reallocation to another land use other than conservation (e.g. the creation of a designer ecosystem) will be highly dependent on the local historic occurrence of such shifts due to natural dynamic processes, the strength of the case for irreversibility, and the degree to which the project is primarily focused on establishing the full complement of key ecosystem attributes as distinct from ecosystem services alone.
Where biological degradation cannot be reversed, the next best alternative would be rehabilitation to the highest practicable ecological functionality, with as high as possible similarity to the reference ecosystem.
- Accelerated and irreversible climate change. A changing climate means that all local ecosystems are likely to be changing at faster rates than
in the past; in ways that are difficult to anticipate. Some entire ecosystems will be destroyed (e.g. many marine, coastal, alpine and cool temperate
communities) where no suitable migration habitats exist; while in other ecosystems, species may have a capacity to adapt by genetic selection or migration,
options that are less likely under conditions of fragmentation (Appendix 3).
Climate change is recognised as an anthropogenic degradation pressure that requires urgent and unfaltering mitigation of its causes, mitigation that needs to be embraced by the whole of society. Even with optimal mitigation, however, much of this change is irreversible and therefore becomes part of the environmental background conditions to which species need to adapt or be lost. To assist potential adaptation, target-setting needs to be informed by research into the anticipated effects of climate change on species and ecosystems so that reference ecosystems and restoration targets can be modified as required (Appendix 3). Where fine scale changes in temperature or moisture levels are expected to affect only some species at an individual site, adaptability can be improved by ensuring the restoration includes a high diversity of the site’s other preexisting species, some of which may be suited to the changed conditions. In cases where the climate envelope of the species is expected to shift as a result of climate forecasts, introducing more diverse genetic material of the same species from other parts of a species’ range is often recommended; at least in fragmented landscapes or aquatic environments where migration potential is lower than intact areas (Refer to Appendix 3). As a rule of thumb, managers need to optimise potential for adaptation by retaining and enhancing genetically diverse representatives of the current local species in configurations that increase linkages and optimise gene flow. Such adaptation is maximized where all threats affecting ecosystems (particularly fragmentation) are minimized.