Restoration Goals and Reference Ecosystems

How restoration projects set their targets — using reference ecosystems to define the composition, structure, and function that recovery aims to achieve.

Definition

A reference ecosystem is a model — drawn from intact analogue sites, historical evidence, or ecological theory — that represents the state an ecosystem would likely occupy in the absence of degradation, and that serves as the target against which restoration goals for composition, structure, and function are set.

Scope

This topic covers how the endpoints of ecological restoration are defined: the concept of the reference ecosystem, the use of historical, contemporary, and modelled references, recovery targets for species composition, vegetation structure, and ecological function, and how goals are adjusted where past conditions cannot be recovered. It includes the debate over novel ecosystems and shifting baselines. It excludes the on-the-ground methods used to reach those goals (treated under active and passive restoration techniques) and the metrics used to judge whether goals are met (treated under restoration success and monitoring).

Core questions

• What state should a restoration project aim to recover?
• How is a reference ecosystem identified when no intact analogue remains?
• How are recovery goals expressed for composition, structure, and function?
• What should be done when historical conditions can no longer be restored?

Key concepts

• Reference ecosystem and reference model
• Historical versus contemporary references
• Composition, structure, and function targets
• Shifting baseline syndrome
• Novel ecosystems
• Recovery trajectory

Key theories

The reference ecosystem model

Restoration goals are anchored to a reference ecosystem that describes the composition, structure, and function the site would have without degradation; references may be drawn from intact analogues, historical records, or multiple lines of evidence rather than a single past snapshot.

Novel ecosystems and unattainable baselines

Where altered abiotic conditions, species loss, or invasions make recovery of the historical state impossible, ecosystems may be reorganized into novel configurations, prompting goals based on function and services rather than strict historical fidelity.

Clinical relevance

Clear, reference-based goals are what make restoration outcomes assessable and accountable; vague aims such as 'improve the habitat' cannot be evaluated or held to standards. The choice of reference also has practical consequences, determining which species are planted, how success is judged, and whether projects pursue historical fidelity or focus on ecosystem function under changed conditions.

History

Early restoration aimed loosely to recreate pre-disturbance conditions. The SER Primer formalized the reference-ecosystem concept in 2004, and the International Standards refined it into a multi-attribute recovery model in 2016 and 2019. In parallel, recognition of irreversible change and shifting baselines through the 2000s prompted the influential, and contested, idea of novel ecosystems that loosened strict historical targets.

Debates

Should restoration target historical states or function under novel conditions?

Some argue that under climate change and pervasive human influence, historical reference states are unattainable and goals should emphasize function and resilience; others warn that the novel-ecosystem framing can be used to lower ambition and excuse degradation.

Key figures

• James Aronson
• Richard Hobbs
• Eric Higgs

Seminal works

• ser2004
• gann2019
• hobbs2009

Frequently asked questions

What is a reference ecosystem?

A model of what an ecosystem would look like if it had not been degraded, used as the target for restoration. It is built from intact comparison sites, historical evidence, and ecological knowledge, and describes the species, structure, and processes the project aims to recover.

What if the original ecosystem can no longer be restored?

When climate change, species loss, or altered soils make the historical state unreachable, projects may aim for a functioning ecosystem that delivers biodiversity and services even if it differs from the past — sometimes called a novel ecosystem. This approach is useful but contested, because it can be misused to justify lower goals.