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Restoration ecology is the scientific study and practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human intervention and action, within a short time frame. Restoration ecology emerged as a separate field in ecology in the 1980s.
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] The practice of ecological restoration includes wide scope of projects including: erosion control, reforestation, the use of genetically local native species, removal of non-native species and weeds, revegetation of disturbed areas, daylighting streams, reintroduction of native species, as well as habitat and range improvement for targeted species. The term "ecological restoration" refers to the practice of the discipline of "restoration ecology".
The term restoration ecology is used for the academic study of the process, whereas "ecological restoration" is the term used for the actual project or process by the commercial practitioners.
The process of ecological restoration is unique in land management perspectives, in that the goal is to restore the original or historic native ecosystem of a site, utilizing local native plant species, excluding exotic plants, and to restore the ecosystem to a self-sustainable state, within a certain amount of time.
The aspect of time and performance standards as part of the definition of ecological restoration, has been controversial since the invention of this new profession-- that projects should be completed within a short amount of time, and that the percentage cover of the local native vegetation should be as close to 100% as possible, with less than 1% weed cover. [2]
In the view of biologist E. O. Wilson, "Here is the means to end the great extinction spasm. The next century will, I believe, be the era of restoration in ecology"
Land managers, laypeople, and stewards have been practicing ecological restoration or ecological management for many hundreds, if not thousands of years,[3] yet the scientific field of "restoration ecology" was first identified and coined in the late 1980s by John Aber and William Jordan. The study of restoration ecology has only become a robust and independent scientific discipline over the last two decades[4], and the commercial applications of ecological restoration are still in the process of developing.
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".[5] In fact, estimates of the current extinction rate are 1000 to 10,000 times the normal rate.[6] For many people biological diversity (biodiversity) has an intrinsic value; humans have a responsibility toward other living things, and obligations to future generations.
On a more anthropocentric level, natural ecosystems provide human society with food, fuel and timber. More fundamentally, ecosystem services involve the purification of air and water, detoxification and decomposition of wastes, regulation of climate, regeneration of soil fertility, and pollination of crops. Such processes have been estimated to be worth trillions of dollars annually.[7]
Habitat loss is the leading cause of both species extinctions[6] and ecosystem service decline.[7] There are two ways to reverse this trend of habitat loss: conservation of currently viable habitat and restoration of degraded habitats.
With regard to biodiversity preservation, it should be noted that restoration activities are complementary to, not a substitute for, conservation efforts. Many conservation programmes, however, are predicated on historical bio-physical conditions - i.e. they are incapable of responding to global climate change, and the assemblages "locked in" that become increasingly fragile and liable to catastrophic collapse. In this sense, restoration is essential to provide new spaces for migration of habitats and their associated flora and fauna.[8] Also, conservation biology often has organisms, and not entire ecosystems and their functions, as its focus, and therefore has limited goals and aims.
Restoration ecology, as a scientific discipline, is theoretically rooted in conservation biology. While restoration ecology may be viewed as a sub-discipline of conservation biology, foundational differences exist between the disciplines' approaches, focuses and modes of inquiry.
The fundamental difference between conservation biology and restoration ecology lies in their philosophical approaches to the same problem. Conservation biology attempts to preserve and maintain existing habitat and biodiversity. In contrast, restoration ecology assumes that environmental degradation and population declines are somewhat reversible processes. Therefore, targeted human intervention can lead to habitat and biodiversity recovery and eventual gains. This does not provide, however, an excuse for converting extremely valuable "pristine" habitat into other uses.
First, both conservation biology and restoration ecology have an unfortunate temperate terrestrial bioregion bias. This issue is probably the result of these fields developing in the geopolitical north, and both fields should attempt to reconcile this bias.
Second, perhaps because plants tend to dominate most (terrestrial) ecosystems, restoration ecology has developed a strong botanical bias, while conservation biology is more strongly zoological.[9]
Similarly, the principal systemic levels of interest differ between the disciplines. Conservation biology has historically focused on target individuals (i.e. endangered species), and has thus concentrated on genetic and population level dynamics. Since restoration ecology is aimed at rebuilding a functioning ecosystem, a broader (i.e. community or ecosystem) perspective is necessary.
Finally, since soils define the foundation of any functional terrestrial system, restoration ecology's ecosystem-level bias has placed more emphasis on the role of soil physical and microbial processes.[10]
Conservation biology's focus on rare or endangered species limits the number of manipulative studies that can be performed. As a consequence, conservation studies tend to be descriptive, comparative and unreplicated.[9] However, the highly manipulative nature of restoration ecology allows the researcher to more rigorously test hypotheses. In fact, every restorative activity is, in essence, an experimental test of what limits populations.[4]
Restoration ecology draws on a wide range of ecological concepts.
Disturbance is a change of environmental conditions, which interferes with the functioning of a biological system. Disturbance at a variety of spatial and temporal scales is a natural, and even essential, component of many communities.[11]
Humans have had limited "natural" impacts on ecosystems for as long as humans have existed, however the severity and scope of our modern influences has accelerated in the last few centuries. Understanding and minimizing the differences between modern anthropogenic and "natural" disturbances is crucial to restoration ecology. For example, new forestry techniques that better imitate historical disturbances are now being implemented.
In addition, restoring a fully sustainable ecosystem often involves studying and attempting to restore a natural disturbance regime (e.g., fire ecology).
Ecological succession is the process by which the component species of a community changes over time. Following a disturbance, an ecosystem generally progresses from a simple level of organization (i.e. few dominant species) to a more complex community (i.e. many interdependent species) over a few generations. Depending on the severity of the disturbance, restoration often consists of initiating, assisting or accelerating ecological successional processes.[12]
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.
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. Further, 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 are central goals of restoration ecology.
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 (i.e. no management required), is the ultimate goal of restorative efforts. Because these ecosystem functions are emergent properties of the system as a whole, monitoring and management are crucial for the long-term stability of an ecosystem.
Restoration ecology, because of its highly physical nature, is an ideal testing ground for emerging community ecological principles (Bradshaw 1987). There are also the emerging concepts of inventing new and successful restoration technologies, performance standards, time frames, local genetics, and society's relationship to restoration ecology, and new ethical and religious possibilities, as future topics of discussion and debate.
Community assembly "is a framework that can unify virtually all of (community) ecology under a single conceptual umbrella".[4] 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.[13] Essentially, if all species are fairly ecologically equivalent then random variation in colonization, migration and extinction rates, between species, drive differences in species composition between sites with comparable environmental conditions.
Alternative stable states are discrete species compositional possibilities that may exist within a community. According to assembly theory, differences in species colonization, interspecific interactions and community establishment may result in distinct community species equilibria. A community has numerous possible compositional equilibria that are dependent on the initial assembly. That is, random fluctuations lead to a particular initial community assembly, which affects successional trajectories and the eventual species composition equilibrium.
Multiple stable states is a specific theoretical concept, where all species have equal access to a community (i.e., equal dispersal potential) and differences between communities arise simply because of the timing of each species' colonization.[13]
These concepts are central to restoration ecology; restoring a community involves not only manipulating the timing and structure of the initial species composition, but also working toward a single desired stable state. In fact, a degraded ecosystem may be viewed as an alternative stable state under the altered environmental conditions.[14]
The ecology of ontogeny is the study of how ecological relationships change over the lifetime of an individual. Organisms require different environmental conditions during different stages of their life-cycle. For immobile organisms (e.g. plants) the conditions necessary for germination and establishment may be different from those of the adult stage.[4] As an ecosystem is altered by anthropogenic processes the range of environmental variables may also be altered. A degraded ecosystem may not include the environmental conditions necessary for a particular stage of an organism's development. If a self-sustaining, functional ecosystem must contain environmental conditions for the perpetual reproduction of its species, restorative efforts must address the needs of organisms throughout their development.
Restoration is defined as the application of ecological theory to ecological restoration. However, for many reasons, this can be a challenging prospect. Here are a few examples of theory informing practice.
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 alone was insufficient to insure species diversity in situations where one species may dominate across the range of resource levels. Their findings were consistent with 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 community structure.
"The dynamics of invasive species may depend on their abilities to compete for resources and exploit disturbances relative to the abilities of native species". Seabloom et al. (2003) tested this concept and its implications in a California grassland restoration context. They found native grass species were able to successfully compete with invasive exotics, therefore the possibility exists of restoring an original native grassland ecosystem.
Progress along a desired successional pathway may be difficult if multiple stable states exist. Looking at over 40 years of wetland restoration data Klotzi and Gootjans (2001) argue that unexpected and undesired vegetation assemblies "may indicate environmental conditions are not suitable for target communities". 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.
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