We have entered the UN Decade of Ecosystem Restoration from 2021. It emphasises understanding of restoration and its critical contribution to our economic, social, and environmental objectives. However, ecosystem restoration is no substitute for conservation and both needs to be taken up at varied scales in regions of risk.
Ecosystems are dynamic communities of plants, animals, and microorganisms interacting with their physical environment as functional unit. These communities are being damaged, degraded and at times destroyed completely by human activity. Damage is when there is a harmful impact upon an ecosystem through activities such as selective logging, road building, poaching, and invasions of non-native species. Degradation is the loss of biodiversity and the disruption of an ecosystem’s structure, composition, and functionality. Reasons may include long-term grazing impacts, long-term overfishing or hunting pressure, and persistent invasions by non-native species. Destruction is the most severe level of impact when all macroscopic life is removed and the physical environment is ruined. Ecosystems are destroyed by such activities as land clearing, urbanization, coastal erosion, and mining. Ecological restoration seeks to initiate or accelerate ecosystem recovery following damage, degradation, or destruction.
Restoration refers to the recreation of the conditions needed for recovery so the plants, animals, and microorganisms can carry out the work of recovery themselves. Assisting recovery can be as simple as removing an invasive species or reintroducing a lost species or a lost function (like fire); or as complex as altering landforms, planting vegetation, changing the hydrology, and reintroducing wildlife. The goal of ecological restoration is to return a degraded ecosystem to its historic trajectory, not its historic condition. The ecosystem may not necessarily recover to its former state since contemporary ecological realities, including global climate change, may cause it to develop along an altered trajectory, just as these same realities may have changed the trajectory of nearby undisturbed ecosystems.
The restoration process begins with an assessment of the degraded site. The current site conditions should be thoroughly examined to identify the need for restoration and any potential actions required to restore the site. Restorationists should consider the causes of degradation, the likelihood that the degradation can be reversed or lessened, and the ways in which restoration can be accomplished. Early in the planning process, restorationists should identify the necessary resources (such as funding, labour, equipment, plant materials, and technical knowledge) that directly affect the project’s feasibility. Support and participation from local communities and government institutions early in the planning process and throughout implementation can be invaluable.
A critical step in restoration planning is to establish realistic goals. Pre-disturbance conditions, often represented by nearby “reference sites,” are common restoration targets, although actual targets are tailored to local ecological, social, legal, and economic conditions. In addition, preventing further loss of protected populations or habitat is a common motivator of restoration. Other goals may include erosion control, rangeland forage production, protection of wildlife habitat, and preservation of cultural landscapes. Planning for climate change has become increasingly important. Once the goals of the restoration project have been established, the next step is to outline objectives and identify measures of success.
Clearly articulated objectives and regular assessment of measurable progress toward those objectives provide information on the trajectory and success of the project, including how and when restoration activities should be modified.
In some cases, restoration specialists simply need to remove the source of the disturbance and allow sites to recover naturally through ecological succession. This process is called passive restoration because restoration specialists do not need to take much action. For example, halting agricultural tillage or stemming the overuse of riverbanks by livestock may be enough to bring a site back to a pre-disturbed state.
In other cases, the ecosystem has passed a threshold of degradation, and disturbed sites within it are not able to recover on their own or can only recover very slowly. This is particularly common when soil and water resources have been compromised through erosion, earth-moving activities, or some other major disturbance. To restore such highly disturbed sites, the removal or cessation of the disturbance is only the first step. Restorationists must then engage in active restoration, which starts or accelerates the recovery process or attempts to change the site’s ecological succession.
One component of active restoration is soil rehabilitation and land stabilization. This component includes the restoration of the soil’s or water’s original chemical, biological, and physical characteristics. Examples include applying amendments (such as lime) to improve soil pH, stemming the flow of fertilizers to artificially enriched soil or water, inoculating soils with beneficial microorganisms, and tilling to improve aeration and root penetration.
Another component of active restoration is restoring the plant community. After the site is prepared, restorationists generally select seeds, seedlings, or cuttings for revegetation. Ecological principles related to the assembly of the biological community help explain the long-term consequences of how and when different species are added to a site.
To create a sustainable restored ecosystem, restoration specialists often need to couple the restoration of plants and animals with that of landscape processes and natural disturbances. Some restored sites are relatively small and isolated, which can lead to problems associated with fragmented habitats. Populations in smaller and more isolated habitat patches experience a greater risk of inbreeding, local extinction of species, and negative edge effects (that is, the effects of one habitat on an adjacent habitat). For example, small, narrow, sinuous patches of forest have greater amounts of an edge than larger square or circular patches. As a result, more of their interiors border other ecosystems, which may increase the forest’s exposure to different pests, predators, and weather and climatic conditions than would normally occur in forests with shorter borders and thus more-insulated interiors.
Monitoring and documentation are essential in the restoration process. Regular monitoring guides adaptive management and also determines when and if restoration goals are being met. In some cases, only limited human intervention (followed by appropriate management) may be necessary, while in other cases human intervention may be necessary for decades.
When is restoration complete?
Ecological restoration aims to re-establish a self-organizing ecosystem on a trajectory to reach full recovery. While restoration activities can often place a degraded ecosystem on an initial trajectory of recovery relatively quickly, full recovery of the ecosystem can take years, decades, or even hundreds of years. For example, while we can initiate a forest restoration process by planting trees, for full recovery to be achieved, the site should be a fully functioning forest with mature trees in the age classes representative of a mature native forest. If there were 500-year-old trees in the forest that was destroyed, then the restoration should logically take hundreds of years to achieve full recovery. During that recovery period, unforeseen barriers to recovery may be encountered, or additional restoration activities may become possible at later stages of development. Thus, while individual restoration activities may be completed, in most cases the restoration process continues as the ecosystem recovers and matures.
Over-intensive use, soil erosion, excess fertilizer and pesticides are exhausting many farmlands. Ways to restore them include reducing tillage, using more natural fertilizer and pest control, and growing more diverse crops, including trees. These steps can rebuild carbon stores in soils, making them more fertile so countries can feed their growing populations without using even more land. The restoration of farmland also creates habitats for wildlife.
Forests and trees are being cleared to feed humanity’s hunger for land and resources. Logging, firewood cutting, pollution, invasive pests and wildfires are damaging what remains. Restoring forest ecosystems means replanting and reducing the pressure on forests so that trees re-grow naturally. Food systems are a major driver of forest loss. Reconsidering the way people grow and consume food can help reduce the pressure on forests. Degraded and disused farmland can be ideal for forest restoration, which can also mean nurturing patches of forest and woodland in landscapes that include busy farms and villages.
Safe and abundant water has become a luxury. Freshwater ecosystems have been degraded by pollution, overfishing and infrastructure as well as the extraction of more and more water for irrigation, industry and homes. Restoration means halting pollution, reducing and treating waste, managing demand for water and fish, and reviving vegetation above and below the surface.
Cities and towns can seem like ecological deserts. There’s little room for vegetation amid the houses, roads and factories. Waste and pollution imperil waterways, soils and the air. But urban areas have huge potential for restoration. Citizen groups and municipal authorities can clean up waterways, let bee-friendly plants grow and create urban woodland and other wildlife habitats in parks, schools and other public spaces. Mowing grass less frequently is cheaper for cities and allows nature to thrive. Permeable sidewalks and urban wetlands protect against flooding and pollution. Contaminated industrial areas can be rehabilitated and turned into places for nature and recreation.
There has never been a more urgent need to revive damaged ecosystems than now. Ecosystems support all life on Earth. The healthier our ecosystems are, the healthier the planet – and its people. The UN Decade on Ecosystem Restoration aims to prevent, halt and reverse the degradation of ecosystems on every continent and in every ocean. It can help to end poverty, combat climate change and prevent mass extinction. It will only succeed if everyone plays a part.