Ecological restoration
Ecological restoration, or ecosystem restoration, is the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed.[1] It is distinct from conservation in that it attempts to retroactively repair already damaged ecosystems rather than take preventative measures.[2][3] Ecological restoration can reverse biodiversity loss, combat climate change, and support local economies.[4]
Habitat restoration involves the deliberate rehabilitation of a specific area to reestablish a functional ecosystem. 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. When it is not feasible to restore habitats to their original size or state, designated areas known as wildlife corridors can be established. These corridors connect different habitats and open spaces, facilitating the survival of species within human-dominated landscapes. For instance, marshes serve as critical stopover sites for migratory birds, wildlife overpasses enable animals to safely cross over highways, and protected riparian zones within urban settings provide necessary refuges for flora and fauna.[5] The United Nations named 2021-2030 the Decade on Ecosystem Restoration.[6]
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.[7][8][9] Habitat loss is a leading cause of species extinctions[9] and ecosystem service decline.[10] 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.[11][12] Restoration goals reflect political choices, and restoration goals differ by place and culture.[13][14][15][16]
Definition[edit]
The Society for Ecological Restoration defines restoration as "the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed."[1] Restoration ecology is the academic study of the science of restoration, whereas ecological restoration is the implementation by practitioners.[17] 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, and habitat and range improvement for targeted species.[18] Many scholars and practitioners argue that ecological restoration must include local communities and stakeholders: they call this process the "social-ecological restoration".[19]
There are many reasons to restore ecosystems. Some include:[20]
There are considerable differences of opinion on how to set restoration goals and define their success.[27] As Laura J. Martin writes, "Restoration targets are moral and political matters as well as logistical and scientific ones."[28] 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.
Ecological restoration has generated controversy. 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."[29] Some scientists argue that, though an ecosystem may not be returned to its original state, the functions of a "novel ecosystem" are still valuable.[30]
Ecosystem restoration can mitigate climate change through activities such as afforestation. Forestry-based carbon offsetting is controversial and sometimes critiqued as carbon colonialism.[31] 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.[14][32]
Applications[edit]
Leaf litter accumulation[edit]
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.[47]
Soil heterogeneity effects on community heterogeneity[edit]
Spatial heterogeneity of resources can influence plant community composition, diversity, and assembly trajectory. Baer et al. (2005) manipulated soil resource heterogeneity in a tallgrass prairie restoration project. They found increasing resource heterogeneity, which on its own was insufficient to ensure species diversity in situations where one species may dominate across the range of resource levels. Their findings were consistent with the theory regarding the role of ecological filters on community assembly. The establishment of a single species, best adapted to the physical and biological conditions can play an inordinately important role in determining the community structure.[48]
Invasion and restoration[edit]
Restoration is used as a tool for reducing the spread of invasive plant species many ways. The first method views restoration primarily as a means to reduce the presence of invasive species and limit their spread. As this approach emphasizes the control of invaders, the restoration techniques can differ from typical restoration projects.[49][50] The goal of such projects is not necessarily to restore an entire ecosystem or habitat.[51] These projects frequently use lower diversity mixes of aggressive native species seeded at high density.[52] They are not always actively managed following seeding.[53] The target areas for this type of restoration are those which are heavily dominated by invasive species. The goals are to first remove the species and then in so doing, reduce the number of invasive seeds being spread to surrounding areas. An example of this is through the use of biological control agents (such as herbivorous insects) which suppress invasive weed species while restoration practitioners concurrently seed in native plant species that take advantage of the freed resources.[54] These approaches have been shown to be effective in reducing weeds, although it is not always a sustainable solution long term without additional weed control, such as mowing, or re-seeding.[50][53][55][56]
Restoration projects are also used as a way to better understand what makes an ecological community resistant to invasion. As restoration projects have a broad range of implementation strategies and methods used to control invasive species, they can be used by ecologists to test theories about invasion.[53] Restoration projects have been used to understand how the diversity of the species introduced in the restoration affects invasion. We know that generally higher diversity prairies have lower levels of invasion.[57] The incorporation of functional ecology has shown that more functionally diverse restorations have lower levels of invasion.[58] Furthermore, studies have shown that using native species functionally similar to invasive species are better able to compete with invasive species.[59][60] Restoration ecologists have also used a variety of strategies employed at different restoration sites to better understand the most successful management techniques to control invasion.[61] To develop restoration ecology into a full science and to improve its practice requires generalizations about the processes governing the development of restored communities. While new experiments can be designed , one way forward is to use data from existing restoration studies to relate plant species performance to their ecological trait.[62]
Successional trajectories[edit]
Progress along a desired successional pathway may be difficult if multiple stable states exist. Looking over 40 years of wetland restoration data, Klötzli and Gootjans (2001) argue that unexpected and undesired vegetation assemblies "may indicate that environmental conditions are not suitable for target communities".[63] Succession may move in unpredicted directions, but constricting environmental conditions within a narrow range may rein in the possible successional trajectories and increase the likelihood of the desired outcome.[64][65]
Sourcing land for restoration[edit]
A study quantified climate change mitigation potentials of 'high-income' nations shifting diets – away from meat-consumption – and restoration of the spared land. They find that the hypothetical dietary change "could reduce annual agricultural production emissions of high-income nations' diets by 61% while sequestering as much as 98.3 (55.6–143.7) GtCO2 equivalent, equal to approximately 14 years of current global agricultural emissions until natural vegetation matures", outcomes they call "double climate dividend".[66][67]
Sourcing material for restoration[edit]
For most restoration projects it is generally recommended to source material from local populations, to increase the chance of restoration success and minimize the effects of maladaptation.[68] However the definition of local can vary based on species, habitat and region.[69] US Forest Service recently developed provisional seed zones based on a combination of minimum winter temperature zones, aridity, and the Level III ecoregions.[70] Rather than putting strict distance recommendations, other guidelines recommend sourcing seeds to match similar environmental conditions that the species is exposed to, either now, or under projected climate change. For example, sourcing for Castilleja levisecta found that farther source populations that matched similar environmental variables were better suited for the restoration project than closer source populations.[71] Similarly, a suite of new methods are surveying gene-environment interactions in order to identify the optimum source populations based on genetic adaptation to environmental conditions.[72][73]
Contrasting restoration ecology and conservation biology[edit]
Both restoration ecologists and conservation biologists agree that protecting and restoring habitat is important for protecting biodiversity. However, conservation biology is primarily rooted in population biology. Because of that, it is generally organized at the population genetic level and assesses specific species populations (i.e. endangered species). Restoration ecology is organized at the community level, which focuses on broader groups within ecosystems.[97]
In addition, conservation biology often concentrates on vertebrate and invertebrate animals because of their salience and popularity, whereas restoration ecology concentrates on plants. Restoration ecology focuses on plants because restoration projects typically begin by establishing plant communities. Ecological restoration, despite being focused on plants, may also have "umbrella species" for individual ecosystems and restoration projects.[97] For example, the Monarch butterfly is an umbrella species for conserving and restoring milkweed plant habitat, because Monarch butterflies require milkweed plants to reproduce. Finally, restoration ecology has a stronger focus on soils, soil structure, fungi, and microorganisms because soils provide the foundation of functional terrestrial ecosystems.[98][99]
The Society for Ecological Restoration (SER) released the second edition of the International Standards for the Practice of Ecological Restoration on September 27, 2019, in Cape Town, South Africa, at SER's 8th World Conference on Ecological Restoration.[100] The publication provides updated and expanded guidance on the practice of ecological restoration, clarifies the breadth of ecological restoration and allied environmental repair activities, and includes ideas and input from a diverse international group of restoration scientists and practitioners.
The second edition builds on the first edition of the Standards, which was released December 12, 2016, at the Convention on Biological Diversity's 13th Conference of the Parties in Cancun, Mexico. The development of these Standards has been broadly consultative. The first edition was circulated to dozens of practitioners and experts for feedback and review. After release of the first edition, SER held workshops and listening sessions, sought feedback from key international partners and stakeholders, opened a survey to members, affiliates and supporters, and considered and responded to published critiques.
The International Principles and Standards for the Practice of Ecological Restoration:
Traditional ecological knowledge[edit]
Traditional ecological knowledge (TEK) from Indigenous Peoples demonstrates how restoration ecology is a historical field, lived out by humans for thousands of years.[120] Indigenous people have acquired ecological knowledge through observation, experience, and management of the natural resources and the environment around them. In the past, they managed their environment and changed the structure of the vegetation to not only meet their basic needs (food, water, shelter, medicines) but also to improve desired characteristics and even increasing the populations and biodiversity. In that way, they achieved a close relationship with the environment and learned lessons that indigenous people keep in their culture.[101]
This means there is much that could be learned from local people indigenous to the ecosystem being restored[121] because of the deep connection and biocultural and linguistic diversity of place.[122] The use of natural resources by indigenous people considers many cultural, social, and environmental aspects, since they have always had an intimate connection with the animals and plants around them over centuries since they obtained their livelihood from the environment around them.[123]
Restoration ecologists must consider that TEK is place dependent due to intimate connection[124] and thus when engaging Indigenous Peoples to include knowledge for restoration purposes, respect and care must be taken to avoid appropriation of the TEK.[125] Successful ecological restoration which includes Indigenous Peoples must be led by Indigenous Peoples[125] to ensure non-indigenous people acknowledge the unequal relationship of power.[126]
For example, the California Indians have a rigid and complex harvesting, management and production practice, largely typical horticultural techniques and concentrated forest burning. The California Indians had a rich knowledge of ecology and natural techniques to understand burn patterns, plant material, cultivation, pruning, digging; what was edible vs. what was not. This knowledge extends into wildlife management – how abundant, where the distribution was, and how diverse the large mammal population was.[127] While the United States has counteracted the degradation, fragmentation and loss of habitat through land set aside from all human influence, indigenous practices could inform ecosystem restoration and wildlife management.[127]