Ecological restoration, or ecosystem restoration, is the process of assisting the recovery of an ecosystem that has been degraded, damaged, destroyed or transformed. It is distinct from conservation in that it attempts to retroactively repair already damaged ecosystems rather than take preventative measures. Ecological restoration can help to reverse biodiversity loss, combat climate change, support the provision of ecosystem services and support local economies. The United Nations has named 2021–2030 the Decade on Ecosystem Restoration.
Habitat restoration involves the deliberate rehabilitation of a specific area to reestablish a functional ecosystem. This may differ from historical baselines (the ecosystem's original condition at a particular point in time). To achieve successful habitat restoration, it is essential to understand the life cycles and interactions of species, as well as the essential elements such as food, water, nutrients, space, and shelter needed to support species populations.
Scientists estimate that the current species extinction rate, or the rate of the Holocene extinction, is 1,000 to 10,000 times higher than the normal, background rate. Habitat loss is a leading cause of species extinctions and ecosystem service decline. Two methods have been identified to slow the rate of species extinction and ecosystem service decline: conservation of quality habitat and restoration of degraded habitat. The number and size of ecological restoration projects have increased exponentially in recent years, with hundreds of thousands of projects across the globe.
Restoration goals reflect political choices, and differ by place and culture. On a global level, the concept of nature-positive has emerged as a societal goal to achieve full nature recovery by 2050, including through restoration of degraded ecosystems to reverse biodiversity loss.
Ecological restoration has become an important global strategy for conserving biodiversity, and maintaining ecosystem services. Restoration initiatives often aim to return ecosystems to their original conditions, or improve an ecosystem's ecological integrity and function.
Definition
The Society for Ecological Restoration defines restoration as "the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed." Restoration ecology is the academic study of the science of restoration, whereas ecological restoration is the implementation by practitioners. Ecological restoration includes a wide diversity of methods including erosion control, reforestation, removal of non-native species and weeds, revegetation of disturbed areas, daylighting streams, the reintroduction of native species, habitat and range improvement for targeted species and establishing wildlife corridors. Many scholars and practitioners argue that ecological restoration must include local communities and stakeholders: they call this process the "social-ecological restoration".Fernández‐Manjarrés, J.F., Roturier, S. and Bilhaut, A.‐G. (2018), The emergence of the social‐ecological restoration concept. Restor Ecol, 26: 404–410.
The goal of ecosystem restoration depends on the specific context of each location. Traditionally, the aim has been to return ecosystems to a past state (historic baseline), based on the idea that past conditions represent a 'pristine' or ideal functioning state. However, this approach is now questioned because human-driven environmental changes, including climate change, continuously alter ecosystems, resulting in a shifting baseline. Today, it's widely recognized that there may be several possible targets for restoration, based on a range of factors. Targets are set based on factors such as the level of ecosystem degradation, how much ecosystem functionality can realistically be restored, local community views, and the costs of restoration efforts.
Restoration efforts aim to support self sustaining ecological processes, and further support interactions within ecosystems.
Rationale There are many reasons to restore ecosystems. Some include:
Restoring natural capital such as drinkable water or wildlife populations Restoring environmental degradation Helping human communities and the ecosystems upon which they depend adapt to the impacts of climate change (through ecosystem-based adaptation) Mitigating climate change (e.g. through carbon sequestration) Helping threatened or endangered speciesSilva, S., Lowry, M., Macaya-Solis, C., Byatt, B., & Lucas, M. C. (2017). Can navigation locks be used to help migratory fishes with poor swimming performance pass tidal barrages? A test with lampreys. Ecological engineering, 102, 291–302 Aesthetic reasons Moral reasons: human intervention has unnaturally destroyed many habitats, and there exists an innate obligation to restore these destroyed habitats Regulated use/harvest, particularly for subsistence Cultural importance to indigenous people The environmental health of nearby populations
There are considerable differences of opinion on how to set restoration goals and define their success. As Laura J. Martin writes, "Restoration targets are moral and political matters as well as logistical and scientific ones." Some restorationists urge active restoration (e.g. killing invasive animals) and others believe that protected areas should have the bare minimum of human interference, such as rewilding.
Skeptics doubt that the benefits justify the economic investment or point to failed restoration projects and question the feasibility of restoration altogether. It can be difficult to set restoration goals because, as Anthony Bradshaw writes, "ecosystems are not static, but in a state of dynamic equilibrium." Some scientists argue that, though an ecosystem may not be returned to its original state, the functions of a "novel ecosystem" are still valuable.
Ecosystem restoration can mitigate climate change through activities such as afforestation. However, afforestation can have negative impacts on biodiversity especially when considering tree-planting initiatives in tropical savannas. The impacts of afforestation on water supply and quality are also debated and vary by region, climate and age of afforestation projects. Forestry-based carbon offsetting is controversial and sometimes critiqued as carbon colonialism. Another driver of restoration projects in the United States is the legal framework of the Clean Water Act, which often requires mitigation for damage inflicted on aquatic systems by development or other activities.
Theoretical foundations Ecological restoration draws on a wide range of ecological concepts.
Disturbance
Disturbance is a change in environmental conditions that disrupt the functioning of an ecosystem. Disturbance can occur at a variety of spatial and temporal scales, and is a natural component of many communities. For example, many forest and grassland restorations implement fire as a natural disturbance regime. However the severity and scope of anthropogenic impact has grown in the last few centuries. Differentiating between human-caused and naturally occurring disturbances is important if we are to understand how to restore natural processes and minimize anthropogenic impacts on the ecosystems.
Succession
Ecological succession is the process by which a community changes over time, especially following a disturbance. In many instances, an ecosystem will change from a simple level of organization with a few dominant pioneer species to an increasingly complex community with many interdependent species. Restoration often consists of initiating, assisting, or accelerating ecological successional processes, depending on the severity of the disturbance. Following mild to moderate natural and anthropogenic disturbances, restoration in these systems involves hastening natural successional trajectories through careful management. However, in a system that has experienced a more severe disturbance (such as in urban ecosystems), restoration may require intensive efforts to recreate environmental conditions that favor natural successional processes.
Fragmentation
Habitat fragmentation describes spatial discontinuities in a biological system, where ecosystems are broken up into smaller parts through land-use changes (e.g. agriculture) and natural disturbance. This both reduces the size of the population and increases the degree of isolation. These smaller and isolated populations tend to be more vulnerable to extinction. Fragmenting ecosystems decreases the quality of the habitat. The edge of a fragment has a different range of environmental conditions and therefore supports different species than the interior. Restorative projects can increase the effective size of a population by adding suitable habitat and decrease isolation by creating habitat corridors that link isolated fragments. Reversing the effects of fragmentation is an important component of restoration ecology. The composition of the surrounding landscape can also influence the effectiveness of restoration projects. For example, a restoration site that is closer to remaining vegetation will be more likely to be naturally regenerated through seed dispersal than a site that is further away.
Ecosystem function Ecosystem function describes the most basic and essential foundational processes of any natural systems, including nutrient cycles and energy fluxes. An understanding of the complexity of these ecosystem functions is necessary to address any ecological processes that may be degraded. Ecosystem functions are emergent properties of the system as a whole, thus monitoring and management are crucial for the long-term stability of ecosystems. A completely self-perpetuating and fully functional ecosystem is the ultimate goal of restorative efforts. We must understand what ecosystem properties influence others to restore desired functions and reach this goal.
Community assembly
Community assembly "is a framework that can unify virtually all of (community) ecology under a single conceptual umbrella". Community assembly theory attempts to explain the existence of environmentally similar sites with differing assemblages of species. It assumes that species have similar niche requirements, so that community formation is a product of random fluctuations from a common species pool. Essentially, if all species are fairly ecologically equivalent, then random variation in colonization, and migration and extinction rates between species, drive differences in species composition between sites with comparable environmental conditions.
Population genetics Genetic diversity has shown to be as important as species diversity for restoring ecosystem processes. Hence ecological restorations are increasingly factoring genetic processes into management practices. Population genetic processes that are important to consider in restored populations include founder effects, inbreeding depression, outbreeding depression, genetic drift, maladaption and gene flow. Such processes can predict whether or not a species successfully establishes at a restoration site.
Applications
Leaf litter accumulation Leaf litter accumulation plays an important role in the restoration process. Higher quantities of leaf litter hold higher humidity levels, a key factor for the establishment of plants. The process of accumulation depends on factors like wind and species composition of the forest. The leaf litter found in primary forests is more abundant, deeper, and holds more humidity than in secondary forests. These technical considerations are important to take into account when planning a restoration project.
Soil heterogeneity effects on community heterogeneity