Download Chapter 13 - Restoration

BCB 341: Principles of
Conservation Biology
RESTORATION ECOLOGY
Lecturer: James Reeler
INTRODUCTION TO RESTORATION
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Many areas are partly destroyed or degraded through human action.
This need not be a permanent state of affairs
Restoration is possible on a local basis provided materials (reservoir
of local species) and expertise are present
Provides an opportunity to put research findings into practise
Great potential for enlarging and
connecting conservation areas
May be a misuse of resources –
pros and cons of restoration must
be added carefully
The active corollary to conservation
biology – rather than protecting
areas that are under threat, it
attempts to increase the extent of
“natural” areas
TERMS
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Ecological restoration – the practice of restoration.
“The process of intentionally altering a site to establish a defined,
indigenous, historic ecosystem. The goal of this process is to emulate
the structure, function, diversity and dynamics of the specified
ecosystem” (society of Ecological Restoration, 1991)
Restoration ecology – the science of restoration (refers to research
and study of restored populations, communities & ecosystems.
Mitigation process (offsets) – where a new site (often incorporating
wetland areas) is created or rehabilitated as a substitute for another
area which is destroyed or undergoing development.
Reference sites - areas with a comparable species composition and
ecosystem structure that are used to determine appropriate
introductions and processes for a restoration site.
WHY RESTORE?
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Disturbance and damage to an ecosystem can be a
natural process (eg: lightning-triggered fires)
In this case, recovery to a stable climax community
raises the biological diversity briefly and undergoes a
process of succession
Some systems may be so damaged that they are unable
to recover by themselves:
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Mine sites/dumps – high erosion rate, potential soil toxicity,
low nutrient status
Areas where degrading agent is still present cannot undergo
restoration (eg: overgrazed areas)
Where original species assemblage has been extensively
eliminated with no source of colonists
INCENTIVES FOR RESTORATION
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Material benefits:
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Existential reasons:
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Economy depends on balance between developed & natural areas
(ecosystem service)
(eg) costs money to clean polluted water, but natural sources provide it
free
If development impinges on ecosystem function too heavily, the
economy & quality of human life deteriorates
Improves personal relationships with nature (especially when conducted
at a community level)
Empowers people and stimulates stewardship
Heuristic reasons:
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Allows the study of ecosystem services through reassembly
Trial & error through hypothesis construction & testing (restoration
ecology)
APPROACHES TO RESTORATION1
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No action
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Rehabilitation
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Replace degraded ecosystem with another, using simple species
assemblage (eg: turn degraded forest into productive pasture)
Establishes a functioning community on site & restores ecosystem
services
Partial restoration
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Too expensive
Previous attempts have failed
System may be able to recover on its own (eg: agricultural fields
returning to the wild)
Restore some ecosystem functions & some original species
Start with hardy local species, leaving rare species for later efforts
Complete restoration
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Restore complete original species composition, structure & function
through a comprehensive reintroduction process
APPROACHES TO RESTORATION2
Ecosystem
function
Replacement using a
few species
(rehabilitation)
Replacement using
many species
(rehabilitation)
ORIGINAL
ECOSYSTEM
Biomass, nutrient content, etc.
Complete restoration to original
Partial restoration
No action; ecosystem recovers on its
own via succession
DEGRADED ECOSYSTEM
No action; continued deterioration
Ecosystem
structure
Number of species & ecosystem complexity
CASE STUDY: THE HEATH FRITILLARY3
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Mellicta athalia has declined rapidly in England
since 1950.
Relies on woodland habitats
Larvae eat common cow wheat, Melanpyrum
pratense, which is found in clearings
Adults require hot sunny clearings in woods for flight, mating &
oviposition
Historically, these were provided by the practice of coppicing –
different areas cut every year
By early 20th century, coppicing was no longer economic, & was
abandoned
Identification of this process had dual impacts:
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Showed a management practice that would correct the problem
Demonstrates a method of restoration for whole communities in the
English countryside dependent on rotational coppicing
Restoration programme in the 1980s was very successful
CASE STUDY: THE LARGE COPPER4
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Extinct in England due to removal of wetland
habitats in East Anglia
Research undertaken in Netherlands to assess
possibility of restoration in England
Males require open fen meadows with nectar
plants as territory – network of sites is needed
Eggs laid on water dock (Rumex hydrolapathum) on habitat edges in
sunny areas. Not found in open areas of male habitats
Dispersal pattern indicates a mosaic of landscape habitats is required
for survival.
Currently sufficient foodplants, but insufficient male territory, & too
many movement barriers
Fen restoration project advocates restoration of areas of open fen &
reedland, which would also allow reintroduction of the species
Illustrates restoration must take into account landscape-level &
microhabitat requirements
IMPLICATIONS OF THESE EXAMPLES
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Autecolocial studies are necessary to reveal complex linkages between
species & environment
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Single species can act as the focus for restoration
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Often hard to carry out restoration due to lack of knowledge of the goal
Endangered species within the habitat can act as a focus and show the
ecosystem function
Flagship species also provide a public focus for the project
Rare species challenge us to restore complex communities
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These species-environment linkages are essential & must be studied before
carrying out restoration
Where habitats are already influenced by human activities, monitoring & study
outcomes will affect long-term management processes
Complex life cycles & specific habitat requirements in micro- & macro scales
By restoring habitat to near original status, other non-focus species will benefit
Single foci are often insufficient, but with several flagship indicators a
functional system can be constructed.
EASE OF RESTORATION: SOIL
Top and sub soil
removed
Top and sub soil
removed
VEGETATION
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Beachfront revegetation in
Australia
Seeds: large numbers possible
 Seedlings: higher survival rate, especially if viable sites identified5
 Saplings: god survival rate, large time and effort involved in growing and
transporting
Nutrient status may require fertilisation – too much may favour grasses
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Obviously linked to the soil development
If soil is intact, then recovery should be relatively simple,
through a successional process.
In extreme situations, recovery may be limited due to
depleted seed bank or changed soil status
Most common method of accelerating restoration is
bypassing immigration process (may be slow if isolated
from colonisers
Immigration rates affected by dispersal method and
propagule type
Slow migrating species (eg legumes) can be introduced
manually, through collection of seed from a donor site
POLLINATOR COMMUNITY
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Spread and success of many species depends on pollinator presence
(usually insects, sometimes birds/bats/rodents)
Bumblebees required for some spring flowers, but they have a limited
foraging range
If no neighbouring vegetation of the appropriate type, then pollinators
will be absent
Initial restoration may have to focus on
species with generalist pollinators
Synchrony of flowering & pollinator activity
is also a problem
Handel (1997) advocated introducing
sequentially flowering species to ensure
pollen presence for pollinators
May mean compromise between old &
new communities
CASE STUDY: HWANGE COAL MINE
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Mine tailings are carbonaceous shale (very high C content, smoulders on
contact with air)
Tailings covered with subsurface soil from new opencast areas
Soil pH ~3
Initial process – cover sides of dumps with extra soil to prevent erosion
introducing air (subterranean burning); change slope angle
Seed soil with pit ash from coal burning (ph~8). Approximately 3t/ha
required to increase pH to ~5
Planting of low pH tolerant grasses
from local area to fix soil for
movement
Gathering of local tree/shrub seeds
Scarification, growth in nursery,
planting
Watering
Introduction of artificial wetland for
processing mine waste; clay-lined &
seeded with wetland species
CASE STUDY: HWANGE COAL MINE
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Natural succession process initiated.
Nearest natural habitat 1.2km over burning mine dumps!
Years 1-3: limited growth, periodic burning. Grasses successful
Year 4: shrubs increasing in coverage. Pitfall traps catch 15spp ants,
20 beetles. >20 spp butterflies present
Year 5: Numbers of insects present increases, birds arrive as trees
grow.
Year 10: sample show >25 unseeded tree species, several grasses.
Baobabs transplanted!
Overall, the process was very successful
Caveat: Erosion is a big problem. Eventually pit slope walls will be
eroded, initiating large subterranean burns.
Solution: ensure slope vegetation is viable in the long term & make
end walls very thick. Provides time for leaching?
Functional ecosystem sitting on a time bomb
RESTORATION: PROS
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Can be carried out at all scales
Large scale projects tend to be expensive
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Small scale projects more common
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Opportunities for local involvement
Provides education & highlights importance of ecosystem services
Opportunities increasing in developed world:
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allow whole landscapes to become functional ecosystems
link conservation areas
De-intensification of agriculture
Abandonment of agricultural land
Availability of post-industrial sites (often near cities
Developing world:
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Additional opportunities for cultural preservation of land-based cultures
Environmental knowledge: people are less likely to degrade land when
they understand its worth
RESTORATION: CONS
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Generally very expensive, even in
comparison to establishment of
conservation areas
Limits to what it can do – restoration is
not an exact science, and it is unlikely to
provide a fully-functioning ecosystem in
most cases
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Overly optimistic mitigation expectations allow
development to progress in sensitive areas
Last is very important, as offsets are often
provided for large developments
Environmental consultants who carry out EIAs are
developing expertise in restoration, & may profit
from mitigation measures
Claim that mitigation is viable without real
evidence
SUMMARY
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Protecting habitat is more effective than restoring it
Offers positive action to repair some of the damage to
biodiversity
Biggest challenge is understanding the complexity and
interactions of biodiversity and how to make them function
after disturbance
Can be very beneficial to local communities, but can be
misused to argue for translocation schemes/ habitat
creation schemes with little chance of success
Requires constant monitoring to assess success and longterm management to assist in succession processes
Should not be used as an excuse to allow development in
sensitive areas.