The latest IPCC mitigation of climate change report identified natural ecosystems as one of the key solutions for absorbing excess atmospheric carbon dioxide and helping to fight climate change. The biodiversity of our planet is under severe threat, however, and we are losing species at the fastest rate in Earth’s history. Preserving and restoring our wild spaces is critical to humanity’s survival as biodiversity provides the air that we breathe, the medicines to heal us, and the food that we eat.
The rapid rate at which human societies have colonised the world and exploited natural resources has put unsustainable pressure on our ecosystems. Deforestation is still sweeping the globe, destroying ancient forests that are essential for wildlife and storing carbon. We have lost meadows, wetlands, coral reefs, and a multitude of other habitats due to human actions and it is vital that we act now to reverse the damage and preserve the planet and our way of life.
Preserving ecosystems is a matter of introducing and enforcing protected areas, and the parties to the Convention on Biological Diversity are aiming to protect 30% of land and sea areas globally by 2030. But how exactly can we reverse biodiversity loss? There is a growing movement to restore ecosystems, and a multitude of methods for doing so. We take a look at some of the challenges and success stories of ecosystem restoration.
Biodiversity is a term used to describe the astonishing variety and variability of living organisms on planet Earth. Diverse communities of bacteria, fungi, plant, and animal organisms form ecosystems with their physical environment, and the complex web of interconnections within these ecosystems is the basis of biodiversity. The complexity of these interconnections is the result of millions of years of evolution and is one of the key reasons that maintaining biodiversity is so important. Every species relies on other species for food, shelter, and reproduction, and the local extinction or introduction of any one species can have a dramatic chain reaction of consequences for the ecosystem.
Higher biodiversity stabilises ecosystems against environmental change, invasive species and disease, and improves resilience to disturbance and potentially climate change. Higher biodiversity also increases the productivity of an ecosystem, which has been recorded in zones where Marine Protected Areas have been introduced, and increased fishing yields in the area and nearby seas by five times. Increased resilience within an ecosystem makes the provision of ecosystem services such as food, water, or flood defence more reliable. Ecosystem services are inextricably linked to biodiversity, and they have an economic cost too, having been valued at $33 trillion a year globally in a 1997 study.
It has been estimated that we are using the equivalent of 1.6 Earths in terms of resources, far exceeding the planetary boundaries that define the safe limits for human impact on natural systems. For example, 96% of mammal biomass is humans and livestock, and 70% of bird biomass globally is domestic poultry. Our food production has an enormous impact on the planet, with 38% of global land surface being dedicated to agriculture. This has had a dramatic effect on ecosystems, with 87% of inland wetlands having disappeared since 1700, one third of forests having been lost globally, and a current extinction rate that is 100 to 1000 times higher than background levels. It is not just species diversity that is being affected but also the numbers of animals. Animal populations have dropped by 68% since 1970 and it is estimated that only 3% of the Earth’s land surface has animals that have been unaffected by human activities.
The biodiversity within affected ecosystems is threatened predominantly by habitat loss and deforestation as a result of land use change for agriculture and biofuels, but also by climate change, urbanisation, habitat fragmentation, pollution, over harvesting, poaching and invasive species. We are having an almost incalculably large effect on the planet, but also negatively impacting on ourselves because ecosystem degradation is already affecting the well-being of an estimated 40% of the world’s population (3.2 billion people). There are economic consequences to biodiversity loss too and every single year, we lose ecosystem services worth more than 10 per cent of our global economic output.
The UN has declared 2021 to 2030 as the Decade of Ecosystem Restoration to raise the profile of the global biodiversity crisis and inspire international collaboration to find solutions to reversing the damage. The report that launched the decade called on nations to deliver existing commitments to restore ecosystems covering an area larger than China and highlighted that businesses and individuals should also commit to restoring ecosystems. The UN goal for the initiative is to begin a nature-friendly movement that continues beyond the end of the decade.
The Decade on Restoration website showcases projects that have halted or reversed ecosystem degradation and it collates information on techniques and principles to provide a useful resource for practitioners. This facilitates knowledge exchange between projects and creates links between practitioners and those seeking expertise, engaging actors from a broad spectrum of backgrounds. The UN report concluded that restoring ecosystems could play a significant role in fighting climate change, contributing one third of the total mitigation needed by 2030. This means that action which prevents, halts, and reverses habitat degradation is essential if we are to keep global temperature increases below 2°C. The report also details the economic incentives for restoring ecosystems, as half the world’s GDP is dependent on nature, and every $1 invested in restoration creates up to $30 in economic benefits. The scope of these benefits is considerable, as restoring just 15% of converted lands and stopping further conversion of natural ecosystems could avoid 60% of expected species extinctions.
Ecological restoration is defined as the process of assisting in repairing damage that has been done to natural ecosystems, primarily caused by human activities such as deforestation, pollution, and introducing invasive species. Restoring a degraded habitat relies on an ecological understanding of how the ecosystem functioned before the damage occurred, and detailed surveying can build a picture of the past ecosystem. Ecosystem restoration also needs to look to the future because it is also essential to appreciate how ecological succession will act on the site once the restoration process begins. This includes taking into account how natural disturbances such as wildfires need to be incorporated into long-term management. In some areas it is sufficient to stop the management of a site (e.g. stopping ploughing or grazing) to allow succession to proceed, a process known as natural regeneration. However, on sites that have been more modified, intensive geological engineering or water improvement may be required using more interventionist techniques.
Ecological restoration takes a different approach from traditional conservation, which has used enigmatic animal species such as giant pandas as a flagship, restoring or preserving habitat to suit that species. This can come at the expense of other species within the same habitat, as demonstrated by the steep declines in other mammals such as snow leopards seen in giant panda reserves. Ecological restoration focuses primarily on building plant and fungal communities, using the principle that animals will use the space once created. In some instances this can be bolstered by targeted reintroductions of animal species such as dormice or amphibians. Reintroductions are particularly useful where the native habitat has become fragmented and animals do not have the means to repopulate the area. Prior to any restoration project an assessment of the site is required, to decide on the required methodology, determine the desired ecological outcomes, identify stakeholders, and formulate a long-term management plan.
Ecological restoration techniques cover a vast array of methods, as different habitats require different interventions, and have been subject to much analysis to determine their success rates. Techniques can include solutions as varied as planting trees, seeding meadows, reconstructing reefs, breaching sea walls, releasing apex predators, building wildlife corridors over motorways, and using nest boxes. Traditionally restoration techniques have been divided into two categories, passive and active restoration. Passive restoration involves removing a source of disturbance (e.g. halting deforestation or removing pollution), and allowing the natural regeneration of the ecosystem to occur. Active restoration is characterised by further intervention (e.g. planting trees, removing topsoil, sowing seed) and is associated with more degraded habitats.
The consensus of metanalyses seems to be that using passive restoration and facilitating natural regeneration gives better results, but the biases in analyses have been questioned as it is difficult to start with two habitats in an identical state. In a highly modified landscape such as the UK, where we have many invasive species and a successional tendency towards forest, even passive rewilding projects such as those on the Knepp Estate can require changes in river courses and tailored grazing regimes to restore rare habitats. Restoration does not need to come at the expense of food production, as techniques such as regenerative agriculture (which includes halting ploughing and using crop rotation) can include producing food as part of their ecosystem services benefits.
One of the most challenging aspects of increasing biodiversity and restoring ecosystems is determining the metrics used to measure successful outcomes. Measuring biodiversity is notoriously complex and looking at a metric such as number of species risks oversimplifying the abundance and rarity of different species within ecosystems. In the UK, construction projects are now required to show a 10% net gain of biodiversity and as part of the monitoring programme to enable this, DEFRA has created a biodiversity metric. The new metric works by assessing the baseline habitat characteristics and then the subsequent habitat type after works have been completed. The metric is calculated based on distinctiveness, condition, and strategic importance, and results in a score expressed in biodiversity units that is independent of site area, and is comparable across projects. The metric calculation will be backed up with an assessment by DEFRA to ensure that the project goals have been met. Alternative metrics include using targeted species surveys or tracing DNA in water and soil (eDNA) to assess presence or absence of species. Vegetation surveys can be done with visual surveys on the site or using remote sensing technology.
The success of ecosystem restoration projects can be easier to determine if clear goals are set out. Having defined the intended target ecosystem, success is usually measured by assessing whether that community of species has been reached, and whether the site will continue to function as the desired ecosystem without too much further intervention. This includes an assessment of the functional species groups within the ecosystem that will ensure its ongoing stability. The restored ecosystem must have the resources within it to sustain the species present to secure its longevity. Any sources of disturbance or pollution should have been eliminated so that the ecosystem can be relatively self-sustaining, subject to normal environmental fluctuations.
Many ecosystems require management to ensure that they are maintained in their current state and restored habitats are no exception. For example many habitats in the UK will rapidly be colonised by scrub vegetation without tree cover, and transitory habitats such as meadows require regular grazing to avoid grass species becoming dominant. Invasive species such as rhododendron must also be monitored and eliminated as they can rapidly take over a habitat if left unchecked. Woodland can require management such as coppicing and thinning to clear rides for butterflies, and heathland requires intermittent and controlled burning as the species have become adapted to wildfires. Maintenance practices need to be drawn into any site management plans to ensure that the habitat remains in the best possible condition.
Another controversial aspect of ecosystem restoration is that some habitats require apex predators to control herbivores lower down the food chain. Otherwise grazing herbivores such as deer can become too numerous and inflict too much damage on vegetation. The introduction of predators like wolves or ecosystem engineers such as beavers requires careful consultation with local stakeholders and can include compensation schemes for damaged stock. If these keystone species are not reintroduced, then interventionist management such as culling of herbivores may become necessary and that also requires careful communication with stakeholders and the public.
The UN Decade of Ecosystem Restoration puts social integration at the very heart of restoration projects. Involving local communities with projects is essential to their success and longevity. This means taking into consideration how people use a site, the historical and cultural importance of a site, and the resources that have been or could be provided by the site. By engaging people at the inception of a project, we can ensure that ecosystem services are recognised, and that biodiversity is acknowledged as being critical to human wellbeing, instead of being considered as something apart from us.
One of the most amazing biodiversity restoration success stories is Costa Rica, the only tropical country that has not only halted but reversed deforestation. Between 1940 and 1983, Costa Rica lost around 50% of its original forest, but work since then has restored forest cover from 24% to 60% of the land area. This has been achieved through offering payments to landowners and farmers to restore forest and backed up by investment in sustainable ecotourism. It is an astonishing turnaround and one that provides a template for other governments to follow. Paying for ecosystem services and linking it to social initiatives is a model that works and can be replicated elsewhere.
Another success story involving natural regeneration is that of Lyme Bay, where a trawling exclusion since 2008 has resulted in marine biodiversity flourishing, including a fourfold increase in reef diversity. This project involved reducing damage and overharvesting and allowing species communities to repopulate naturally. The restoration has increased productivity in the bay, demonstrating again that restoring biodiversity increases productivity and shows real ecosystem services benefits for the community. Again, the project involved significant involvement of local stakeholders.
Restoration projects can be extraordinary in scale, such as the UN’s flagship Great Green Wall project. The Great Green Wall aims to re-green the width of Africa, restoring 100 million hectares of forest by 2030. Converting degraded agricultural land through forestry and silviculture will transform a vast swathe across the middle of Africa into productive land. In China, ecosystem restoration has even succeeded in converting desert into productive farmland or forest. China has also implemented the ’Green Wall of China’, incentivising farmers to plant trees and hold back the advance of the Gobi Desert.
Although the scale of the biodiversity crisis is alarming, we have the tools and frameworks at our fingertips to effect ecosystem restoration that can reduce extinctions, increase productivity, and have significant social benefits. With businesses and governments focusing on increasing biodiversity, it is going to become increasingly important that we monitor and quantify the benefits of works carried out. Projects that are well thought out can implement real-world change with a multitude of benefits for the planet and people.