Back to nature - restore or rewild?

As our climate changes, how should we revive our ecologically degraded landscapes? Should we restore what is lost, or bring in what may thrive? Nathalie Pettorelli report

Our world is in a climate emergency. Rapid changes in climatic conditions, driven by anthropogenic greenhouse-gas emissions, pose an existential threat to societies around the world.

This climate emergency is happening against a biodiversity crisis that is just as severe and far-reaching. Around 1 million animal and plant species face extinction, wildlife populations are widely declining and extinction rates are several orders of magnitude higher than the natural norm.

The climate change and biodiversity crises are fundamentally connected. We are losing wildlife at an incredibly fast rate due to habitat loss, pollution and invasive species – and because our climate is changing.

This rapid loss of biodiversity accelerates climate change, decreasing the Earth’s capacity to sequester and store the carbon we emit and reducing opportunities for our societies to adapt to the new climatic normal. That linkage makes it critical to boost nature recovery, to address the climate and the biodiversity crises.

Nature’s hand

This imperative contributed to the United Nations designating 2021–2030 the UN Decade on Ecosystem Restoration. It’s why the recent Conference of the Parties (COP27) of the UN Framework Convention on Climate Change (UNFCCC) included nature-based solutions in its cover decision.

The International Union for Conservation of Nature (IUCN) defines nature-based solutions as “actions to protect, sustainably manage and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits”.

Examples of nature-based solutions to address climate change include restoring ecosystems such as saltmarshes and peatlands. These trap and store carbon at a great rate per area, provide important habitats for local and migrating species and deliver important ecosystem services, such as regulating water flow, protecting coastal areas and cutting flood risk.

It is not easy to identify solutions that benefit and enhance biological diversity in our rapidly changing world.

Until recently, we understood recovering degraded ecosystems to mean bringing them back to known, “healthy” baselines. But the intensity and speed of global environmental changes leads many practitioners and scientists to conclude that we may have already pushed some species far beyond their traditional ranges and some ecosystems far beyond their limits.

In many places, it now makes little sense to force restoration of historical conditions when that environment is changing and will continue to change. In such situations, rewilding may prove a more sensible, cost‐effective way to address declining biodiversity and the associated changes in ecosystem-services delivery.

Rewilding-v-restoration

Rewilding is a developing concept in ecosystem stewardship. This approach can help to reorganise and regenerate nature in an ecologically degraded landscape. Rewilding differs from restoration in several ways. Under a rewilding approach:

• Historical benchmarks are less relevant
• There is less fidelity to taxonomic precedent and the dynamics of rewilded ecosystems is less predictable
• Management commitments are tapered over time
• You accept taxonomic substitutions, environmentally driven system transformation and the fact that new ecosystems may emerge.

Rewilding focuses on ecosystem functioning and promotes minimal management, long-term. It tends to consider larger areas for implementation and to involve lower costs per hectare. But being a relatively novel approach to ecosystem management, rewilding has a thinner knowledge base than we have for classical restoration approaches.

Traditional restoration and rewilding are both examples of nature-based solutions. We need both to bend the curve on biodiversity loss. Getting the implementation right will not be simple. We must consider several gaps in evidence and research to help these biodiversity and climate solutions to deliver what they promise.

We still have a limited general understanding of the short- and long-term biodiversity benefits and disbenefits from deploying nature-based solutions.

Local increases in biodiversity do not automatically imply global biodiversity benefits. Some restoration or rewilding may increase distribution of widespread generalist species but will not benefit species that face extinction.

Similarly, ecosystems’ recovery of above-ground biomass may not significantly increase species diversity. Nature recovery projects can affect different aspects of biodiversity at different scales, enhancing some while losing others.

We lack the right frameworks to compare biodiversity benefits across climate-change mitigation and adaptation projects. This can make it difficult to identify and prioritise which options best deliver for climate and biodiversity.

Uncertain outcomes

Climate change has and will trigger mass movements of species across the world – and of people – which complicates conservation planning. Rapid biodiversity shifts can adversely affect ecosystem functioning, which can make restoration outcomes uncertain.

Climate change may lead to more land being converted to grow crops. This will impact landscape connectivity. It could increase pressures from climate change on neighbouring restored or rewilded ecological systems.

Most efforts to track and understand biodiversity’s redistribution have focused on species. But there is growing evidence that distributions of ecosystems are changing – and will change more in coming decades.

We need to better track and predict which ecosystems are moving and which face collapse because of climate change. That knowledge will help to identify where restoration of existing ecosystems is likely to fail – and where rewilding may be a better option.

We also need to better understand how and where changes in climatic conditions will make nature-based solutions such as restoration and rewilding less effective.

Local climate trajectories will shape restorative actions’ success and pace. Forest regrowth may be slower in hotter, drier climates. Similarly, precipitation anomalies may alter wetlands’ greenhouse-gas emissions, reshaping the carbon benefits of creating or restoring wetlands.

Local climate trajectories have multiple drivers; they are difficult to predict. Without that information, it is difficult to assess and compare different nature-based solutions’ likely long-term outcomes.

Evidence gaps

The temporal and spatial extents of biodiversity loss and climate breakdown have increased significantly in recent decades. Yet the scale of our response has shrunk, in many cases, over the same period. Approaches such as restoration increasingly aim to tackle global threats such as climate change with localised, small-scale projects.

We lack knowledge and evidence to scale up these activities, to turn local actions into larger-scale responses. We need much better evidence to unpick co-dependencies between ecosystems and to understand the telecoupled nature of our world.

Measures that we call nature-based solutions do not always deliver biodiversity benefits. Badly designed and implemented interventions can have catastrophic direct and indirect consequences for biodiversity and for local communities.

Afforesting non-forested areas in species-rich natural dry grasslands can, for example, severely impact local biodiversity and make natural ecosystems less resilient to climate change. We need to build evidence on unwanted consequences from nature-based solutions and to learn from them.

Developing a typology of risks would help us to identify solutions that:

• Will not achieve meaningful climate-change mitigation or adaptation and/or biodiversity objectives on the site in question
• Are culturally inappropriate
• Threaten neighbouring populations of species or ecosystems
• Are unsustainable – whether ecologically, socially or financially – long term.

Nature-based solutions can help us to tackle the climate and biodiversity crises. But for all the reasons I set out here, they need more careful planning and thought – and we need a lot more data and evidence to make that possible.

Because of this, they are not a silver bullet for addressing the climate and biodiversity crises. Instead, we must treat them as an additional, complementary way to address the environmental challenges we face.

Our priority is to rapidly transition all world economies to achieve a sustainable, low-carbon future – and to tackle the underlying, indirect causes of nature loss.

Building that future demands transformative change across societies and economies. It means correcting perverse incentive structures, being more holistic in our decision-making, strengthening and enforcing environmental laws and policies and rethinking our legislative approach to nature management.

We need all of this to better support biodiversity conservation in times of rapid climatic change.

This article first appeared in the May 2023 issue of The Environment magazine. Nathalie Pettorelli is a professor of conservation science at the Institute of Zoology, Zoological Society of London (ZSL)