Rehabilitation of a portion of Johnson Creek, to restore bioswale and
flood control functions of the land which had long been converted to
pasture for cow grazing. The horizontal logs can float, but are anchored
by the posts. Just-planted trees will eventually stabilize the soil.
The fallen trees with roots jutting into the stream are intended to
enhance wildlife habitat. The meandering of the stream is enhanced here
by a factor of about three times, perhaps to its original course.
Restoration ecology emerged as a separate field in ecology in the late twentieth century. It is the scientific study supporting the practice of ecological restoration, which is the practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human intervention and action. Restoration ecology is the academic study of the process, whereas ecological restoration is the actual project or process by restoration practitioners.
Definition
The Society for Ecological Restoration defines "ecological restoration" as an "intentional activity that initiates or accelerates the recovery of an ecosystem with respect to its health, integrity and sustainability".[1] Ecological restoration includes a wide scope of projects including erosion control, reforestation, removal of non-native species and weeds, revegetation of disturbed areas,daylighting streams, reintroduction of native species (preferably native species that have local adaptation), and habitat and range improvement for targeted species.E. O. Wilson, a biologist, states, "Here is the means to end the great extinction spasm. The next century will, I believe, be the era of restoration in ecology."[2]
History
Indigenous peoples, land managers, stewards, and laypeople have been practicing ecological restoration or ecological management for hundreds, if not thousands, of years.[3] However, the scientific field of "restoration ecology" was not first formally identified and coined until the late twentieth century, by John Aber and William Jordan III when they were at the University of Wisconsin-Madison.[4] In the late twentieth century, environmental disasters caused by industry were taking place motivating people toward restoration. They held the first international meetings on this topic in Madison, Wisconsin during which attendees visited the University of Wisconsin-Madison Arboretum—the oldest restoration ecology project made famous by Professor Aldo Leopold.[5] The study of restoration ecology has since become a robust and independent scientific discipline and the commercial applications of ecological restoration have tremendously increased in recent years.[6]Basis for restoration ecology
There is consensus in the scientific community that the current environmental degradation and destruction of many of the Earth's biota is considerable and is taking place on a "catastrophically short timescale".[7] 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.[8][9][10]Many people believe that biodiversity has intrinsic value and that humans have a responsibility to conserve biodiversity, and an obligation to future generations to preserve nature.[11] Natural ecosystems are also known to provide ecosystem services in the form of resources such as food, fuel, and timber; the purification of air and water; the detoxification and decomposition of wastes; the regulation of climate; the regeneration of soil fertility; and the pollination of crops. Such processes have been estimated to be worth trillions of dollars annually.[12][11]
Habitat loss is the leading cause of both species extinctions[10] and ecosystem service decline.[12] Two methods to slow the rate of species extinction and ecosystem service decline are the conservation of currently viable habitat, and the restoration of degraded habitat.
Theoretical foundations
Restoration ecology draws on a wide range of ecological concepts.Disturbance
Disturbance is a change in environmental conditions that disrupts the functioning of an ecosystem. Disturbance, at a variety of spatial and temporal scales, is a natural component of many communities.[13] For example, many forest and grassland restorations implement fire as a natural disturbance regime.Humans previously had a limited impact on ecosystems, but the severity and scope of human impact has grown in the last few centuries. It important to understand and minimize anthropogenic impacts on ecosystems. It is also important to differentiate between human-caused and naturally-occurring disturbances.
Succession
Ecological succession is the process by which the species within a community change over time. Following a disturbance, an ecosystem generally progresses from a simple level of organization (i.e. few dominant pioneer species) to a more complex community (i.e. many interdependent species) over time. Depending on the severity of the disturbance, restoration often consists of initiating, assisting, or accelerating ecological successional processes.[14]In many ecosystems, communities tend to recover following mild to moderate natural and anthropogenic disturbances. Restoration in these systems involves hastening natural successional trajectories. However, a system that has experienced a more severe disturbance (i.e. physical or chemical alteration of the environment) may require intensive restorative efforts to recreate environmental conditions that favor natural successional processes. This ability to recover is called resilience.
Fragmentation
Habitat fragmentation is the emergence of spatial discontinuities in a biological system. Through land use changes (e.g. agriculture) and natural disturbance, ecosystems are broken up into smaller parts. Small fragments of habitat can support only small populations and small populations are more vulnerable to extinction. Furthermore, fragmenting ecosystems decreases interior habitat. Habitat along the edge of a fragment has a different range of environmental conditions and therefore supports different species than the interior. Fragmentation effectively reduces interior habitat and may lead to the extinction of those species which require interior habitat. Restorative projects can increase the effective size of a habitat by simply adding area or by planting habitat corridors that link and fill in the gap between two isolated fragments. Reversing the effects of fragmentation and increasing habitat connectivity can be an important effect of restoration ecology.[15]Ecosystem function
Ecosystem function describes the foundational processes of natural systems, including nutrient cycles and energy fluxes. These processes are the most basic and essential components of ecosystems. An understanding of the full complexity and intricacies of these cycles is necessary to address any ecological processes that may be degraded. A functional ecosystem, that is completely self-perpetuating and does not require management, is the ultimate goal of restorative efforts. Ecosystem functions are emergent properties of the system as a whole, thus monitoring and management are crucial for the long-term stability of ecosystems.[citation needed]Community assembly
Community assembly "is a framework that can unify virtually all of (community) ecology under a single conceptual umbrella".[16] 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.[17] 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.[citation needed]Population genetics
Restoration ecology, and the practice of ecological restoration, must consider population genetic processes in order to ensure that restored populations maintain genetic diversity conducive to population establishment and reproduction. Population genetic processes that can alter restored population genetics include founder effects, inbreeding depression, outbreeding depression, genetic drift, gene flow, and more. Such processes can predict whether or not a species successfully establishes at a restoration site.[18][19]Applications
Soil heterogeneity effects on community heterogeneity
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 insure 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.[20]Invasion and restoration
Restoration is used as a tool for reducing the spread of invasive plant species in a number of 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 control of invaders, the restoration techniques can differ from typical restoration projects.[21][22] The goal of such projects is not necessarily to restore an entire ecosystem or habitat.[23] These projects frequently use lower diversity mixes of aggressive native species seeded at high density. These projects frequently use lower diversity mixes of aggressive native species seeded at high density.[24] They are not always actively managed following seeding.[25] 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. This approach has 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.[22][25][26][27]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, they can be used by ecologists to test theories about invasion.[25] 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.[28] Incorporation of functional ecology has shown that more functionally diverse restorations have lower levels of invasion.[29] Furthermore, studies have shown that using native species functionally similar to invasive species are better able to compete with invasive species.[30][31] Restoration ecologists have also used the variety of strategies employed at different restoration sites to better understand the most successful management techniques to control invasion.[32]
Successional trajectories
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".[33] 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 a desired outcome.Application to ecological restoration
Ecosystem restoration for the superb parrot on an abandoned railway line in Australia
Forest restoration in action at the Buffelsdraai Landfill Site Community Reforestation Project in South Africa
Sources for restoration
During seed based restoration projects, it is generally recommended to source from local populations, to minimize the effects of maladaptation.[34] One of the many challenges of restoration is that every species is different and requires different sourcing guidelines. Rather than putting strict distance recommendations, other guidelines recommend sourcing seeds to match similar environmental conditions. 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.[35] Restoration guidelines vary drastically between states and agency. For example, Minnesota is broken up into 9 seed sourcing zones,[36] where its neighbor Iowa, is broken into three latitudinal zones.[37] US Forest Service recently developed provisional seed zones based on a combination of minimum winter temperature zones, aridity, and the Level III ecoregions.[38]Rationale
There are many reasons to restore ecosystems. Some include:- Restoring natural capital such as drinkable water or wildlife populations
- Mitigating climate change (e.g. through carbon sequestration)
- Helping threatened or endangered species[39]
- Aesthetic reasons [40]
- Moral reasons: Human intervention has unnaturally destroyed many habitats, and there exists an innate obligation to restore these destroyed habitats
Some conservations argue, that though an ecosystem may not be returned to its original state, the functions of the ecosystem (especially ones that provide services to us) may be more valuable than its current configuration (Bradshaw 1987). One reason to consider ecosystem restoration is to mitigate climate change through activities such as afforestation. Afforestation involves replanting forests, which remove carbon dioxide from the air. Carbon dioxide is a leading cause of global warming (Speth, 2005) and capturing it would help alleviate climate change. Another example of a common 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.[citation needed]
Challenges in restoration
Some view ecosystem restoration as impractical, partially because restorations often fall short of their goals. Hilderbrand et al. point out that many times uncertainty (about ecosystem functions, species relationships, and such) is not addressed, and that the time-scales set out for 'complete' restoration are unreasonably short, while other critical markers for full scale restoration are either ignored or abridged due to feasibility concerns.[41] In other instances an ecosystem may be so degraded that abandonment (allowing a severely degraded ecosystem to recover on its own) may be the wisest option.[42] Local communities sometimes object to restorations that include the introduction of large predators or plants that require disturbance regimes such as regular fires, citing threat to human habitation in the area (MacDonald et al. 2002). High economic costs can also be perceived as a negative impact of the restoration process.Public opinion is very important in the feasibility of a restoration; if the public believes that the costs of restoration outweigh the benefits they will not support it (MacDonald et al. 2002).
Many failures have occurred in past restoration projects, many times because clear goals were not set out as the aim of the restoration, or an incomplete understanding of the underlying ecological framework lead to insufficient measures. This may be because, as Peter Alpert says, "people may not [always] know how to manage natural systems effectively".[43] Furthermore, many assumptions are made about myths of restoration such as carbon copy, where a restoration plan, which worked in one area, is applied to another with the same results expected, but not realized (Hilderbrand et al. 2005).
Contrasting restoration ecology and conservation biology
Restoration ecology may be viewed as a sub-discipline of conservation biology, the scientific study of how to protect and restore biodiversity. Ecological restoration is then a part of the resulting conservation movement.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.[44]
In addition, conservation biology often concentrates on vertebrate 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 "poster species" for individual ecosystems and restoration projects.[44] For example, the Monarch butterfly is a poster 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.[45][46]
Science-practice gap
One of the struggles for both fields is a divide between restoration ecology and ecological restoration in practice. Currently, many restoration practitioners as well as scientists feel that science is not being adequately incorporated into ecological restoration projects.[47][48][49][50] In a 2009 survey of practitioners and scientists, the "science-practice gap" was listed as the second most commonly cited reason limiting the growth of both science and practice of restoration.There are a variety of theories about the cause of this gap. However, it has been well established that one of the main issues is that the questions studied by restoration ecologists are frequently not found useful or easily applicable by land managers.[47][51] For instance, many publications in restoration ecology characterize the scope of a problem in depth, without providing concrete solutions.[51] Additionally many restoration ecology studies are carried out under controlled conditions and frequently at scales much smaller than actual restorations.[25] Whether or not these patterns hold true in an applied context is often unknown. There is evidence that these small scale experiments inflate type II error rates and differ from ecological patterns in actual restorations.[52][53]
There is further complication in that restoration ecologists who want to collect large scale data on restoration projects can face enormous hurdles in obtaining the data. Managers vary in how much data they collect, and how many records they keep. Some agencies keep only a handful of physical copies of data that make it difficult for the researcher to access.[54] Many restoration projects are limited by time and money, so data collection and record keeping are not always feasible.[48] However, this limits the ability of scientists to analyze restoration projects and give recommendations based on empirical data.
Natural Capital Committee's recommendation for a 25-year plan
The UK Natural Capital Committee (NCC) made a recommendation in its second State of Natural Capital report published in March 2014 that in order to meet the Government's goal of being the first generation to leave the environment in a better state than it was inherited, a long-term 25-year plan was needed to maintain and improve England's natural capital. The UK Government has not yet responded to this recommendation.The Secretary of State for the UK's Department for Environment, Food and Rural Affairs, Owen Paterson, described his ambition for the natural environment and how the work of the Committee fits into this at an NCC event in November 2012: "I do not, however, just want to maintain our natural assets; I want to improve them. I want us to derive the greatest possible benefit from them, while ensuring that they are available for generations to come. This is what the NCC's innovative work is geared towards".[citation needed]
