Restoration of Degraded habitat
Restoration ecology 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.
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". 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, the reintroduction of native species (preferably native species that
have local adaptation), and habitat and range improvement for targeted species.
Restoration ecology emerged as a
separate field in ecology in the late twentieth century. The term was coined by
John Aber and William Jordan III when they were at the University of
Wisconsin–Madison. However, indigenous peoples, land managers, stewards, and
laypeople have been practicing ecological restoration or ecological management
for thousands of years.
Restoration
ecology 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 are 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.
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, 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:
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.
Invasion
and restoration:
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. The goal of
such projects is not necessarily to restore an entire ecosystem or habitat.
These projects frequently use lower diversity mixes of aggressive native
species seeded at high density. They are not always actively managed following
seeding. 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. 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.
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.
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.
The incorporation of functional ecology has
shown that more functionally diverse restorations have lower levels of
invasion. Furthermore, studies have shown that using native species
functionally similar to invasive species are better able to compete with invasive
species. 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.
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". 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.
Sourcing
material for restoration:
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.
However the definition of local can vary based on species. habitat and region.
Forest Service recently developed provisional seed zones based on a combination of minimum winter temperature
zones, aridity, and the Level III ecoregions. 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.
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.
There
are many reasons to restore ecosystems. Some include:
Restoring natural capital such as
drinkable water or wildlife populations
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
species
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 relevance of native
ecosystems to Native
ronmental health of nearby
populations
.jpeg)
