Restoration ecology emerged as a separate field in ecology in the
1980s. 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. The term "restoration ecology" is therefore commonly used for
the academic study of the process, whereas the term "ecological
restoration" is commonly used for 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".The practice of ecological restoration includes wide
scope of projects such as erosion control, reforestation,
usage 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.
E. O. Wilson, a biologist states that: "Here is
the means to end the great extinction spasm. The next century will, I believe,
be the era of restoration in ecology"
History
Land managers, laypeople, and stewards have been practicing ecological
restoration or ecological management for many hundreds, if not thousands of
years, yet the scientific field of "restoration ecology" was not
first formally identified and coined until the late 1980s, by John Aber and
William Jordan when they were at the University of Wisconsin-Madison.
They held the first international meetings on this topic in Madison during
which attendees visited the University of Wisconsin's Arboretum—the oldest
restoration ecology project made famous by Professor Aldo
Leopold. The study of restoration ecology has only become a robust and independent
scientific discipline over the last two decades, and the commercial
applications of ecological restoration have tremendously increased in recent
years.
Restoration needs
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". Estimates of the current extinction rate is 1000 to 10,000 times
more than the normal rate.For many people biological diversity, (biodiversity)
has an intrinsic value that humans have a responsibility towards other living
things, and an obligation to future generations.
On a more anthropocentric level, natural ecosystems provide
human society with food, fuel and timber. 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.
Habitat loss is the leading cause of both species
extinctions and ecosystem
service decline.The two ways to reverse this trend of habitat loss are conservation of currently viable habitat and
restoration of degraded habitats.
Conservation biology and restoration ecology
With regard to biodiversity preservation, it should be noted
that restoration activities are not a substitute, but are complementary 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" become increasingly
fragile and liable to catastrophic collapses. In this sense, restoration is
essential to provide a new space for migration of habitats and their associated
flora and fauna. Additionally, conservation biology often has organisms, but
not entire ecosystems and their functions, as its focus is towards a narrowed
approach with limited aims.
Restoration ecology, as a scientific discipline is
theoretically rooted in conservation biology. Although, restoration
ecology may be viewed as a sub-discipline of conservation biology, foundational
differences do 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, to some extent, reversible processes. Therefore, targeted human
intervention is used to promote habitat, biodiversity recovery and associated
gains. This does not provide, however, an excuse for converting extremely
valuable "pristine" habitat into other uses.
Focuses
Firstly, 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 the fields should attempt to reconcile this bias.
Secondly, may be because plants tend to dominate most
(terrestrial) ecosystems, restoration ecology has developed a strong botanical
bias, whereas conservation biology is more strongly zoological.
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's physical and microbial processes.
Modes of inquiry
Conservation biology's focus on rare or endangered
species limit the number of manipulative studies that can be performed. As a
consequence, conservation studies tend to be descriptive, comparative and
unreplicated. However, the highly manipulative nature of restoration ecology
allows the researcher to test the hypotheses vigorously. Restorative activity
often reflects an experimental test of what limits populations.
Theoretical foundations
Restoration ecology draws on a wide range of ecological
concepts.
Disturbance
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.
Humans have had limited "natural" impacts on
ecosystems for as long as humans have existed, however, the severity and scope
of our 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).
Succession
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 few generations. Depending on the severity of the
disturbance, restoration often consists of initiating, assisting or accelerating
ecological successional processes.
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 are
the central goals of restoration ecology.
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 (no management required), is the ultimate goal of
restorative efforts. Since, 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.
Evolving concepts
Restoration ecology, because of its highly physical nature,
is an ideal testing ground for an emerging community's ecological principles
(Bradshaw 1987). Likewise, there are 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.
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, migration and extinction rates between species, drive differences
in species composition between sites with comparable environmental conditions.
Stable states
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.
These concepts are central to restoration ecology; restoring
a community not only involves manipulating the timing and structure of the
initial species composition, but also working towards a single desired stable
state. In fact, a degraded ecosystem may be viewed as an alternative stable
state under the altered environmental conditions.
Ontogeny
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. 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.
Application of theory
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.
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.
Invasion, competitive dominance and resource use
"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 that the native grass species were able to
successfully compete with invasive exotics, therefore, the possibility exists
of restoring an original native grassland ecosystem.
Successional trajectories
Progress along a desired successional pathway may be
difficult if multiple stable states exist. Looking over 40 years of wetland
restoration data Klotzi and Gootjans (2001) argue that unexpected and undesired
vegetation assemblies "may indicate that 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.
The 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 (link) 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”.
Ecosystem restoration
According to the Society for Ecological Restoration,
ecosystem restoration is the return of a damaged ecological system to a stable,
healthy, and sustainable state, often together with associated ecosystem services.
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
- Aesthetic reasons (Harris et al. 2006, Macdonald et al. 2002)
- Moral reasons: we have degraded, and in some cases destroyed, many ecosystems so it falls on us to ‘fix’ them.
There are considerable differences of opinion in how to set
restoration goals and how to define their success. Some urge active restoration
(e.g. eradicating invasive animals to allow the native ones to survive) and
others who believe that protected areas should have the bare minimum of human
interference. Ecosystem restoration has generated controversy, with skeptics
who doubt that the benefits justify the economic investment or who point to
failed restoration projects and question the feasibility of restoration
altogether. It can be difficult to set restoration goals, in part because, as
Anthony Bradshaw claims, “ecosystems are not static, but in a state of dynamic
equilibrium…. [with restoration] we aim [for a] moving target.”
Even 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.
Problems with restoration
Some view ecosystem restoration as impractical, in part
because it sometimes fails. 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. In other instances an ecosystem may be so degraded that
abandonment (allowing an injured ecosystem to recover on its own) may be the
wisest option (Holl, 2006). Local communities sometimes object to restorations
that include the introduction of large predators or plants that require disturbance regimes such as regular fires
(MacDonald et al. 2002). High economic costs can also be a 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). In these cases people might be ready to leave the ecosystem to recover
on its own, which can sometimes occur relatively quickly (Holl, 2006).
Many failures have occurred in past restoration projects,
many times because clear goals were not set out as the aim of the restoration.
This may be because, as Peter Alpert says, “people may not [always] know how to
manage natural systems effectively”. Also many assumptions are made about myths
of restoration such as the 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).
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