Disturbance

1
Disturbance
2
Definition

• Disturbance is any relatively discrete event in
  time that disrupts ecosystem, community, or
  population structure and changes resources,
  substrate availability, or the physical
  environment.

3
Intermediate Disturbance Hypothesis
S
Disturbance
4
(No Transcript)
5
Disturbance

• Distribution
• Frequency
• Return Interval
• Rotation period
• Predictability
• Area or size
• Magnitude
• Synergism

6
Patch Dynamic Concept

• In addition to disturbances, patchiness of the
  environment influences diversity of communities
• Diversity increases with increasing patchiness
  until patches as too small to support some species

7
Species-Area Curve

• S cAz
• S Number of species
• C A constant measuring number of species per
  unit area
• A Area
• z A constant measuring the slope of the line
  relating S and A

8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
Species-Area Curve

• z commonly tends to be around 0.3
• You can predict the number of species for
  havitats or ecosystems of differing sizes
• Often used to predict rate of extinction based on
  change in area
• Species number in streams and rivers tends to be
  a function of length more than area

12
(No Transcript)
13
Standards for Ecologically Successful River
Restoration

• The design of an ecological river restoration
  project should be based on a specified guiding
  image of a more dynamic, healthy river that could
  exist at the site.

14
Indicators

• Presence of a design plan or description of
  desired goals that are not orientated around a
  single, fixed and invariable endpoint

15
Standards for Ecologically Successful River
Restoration

• The rivers ecological condition must be
  measurably improved.

16
Indicators

• Water quality improved
• Natural flow regime implemented
• Increase in population viability of target
  species
• Percentage of native vs. non-native species
  increased
• Extent of riparian vegetation increased
• Increased rates of ecosystem functions
• Bioassessment index improved
• Improvements in limiting factors for a given
  species or life stage

17
Standards for Ecologically Successful River
Restoration

• The river system must be more self-sustaining and
  resilient to external perturbations so that only
  minimal follow-up maintenance is needed.

18
Indicators

• Few interventions needed to maintain site
• Scale of repair work required is small
• Documentation that ecological indicators stay
  within a range consistent with reference
  conditions over time

19
Standards for Ecologically Successful River
Restoration

• During the construction phase, no lasting harm
  should be inflicted on the ecosystem.

20
Indicators

• Little native vegetation removed or damaged
  during implementation
• Vegetation that was removed has been replaced and
  shows signs of viability
• Little deposition of fine sediments because of
  implementation process

21
Standards for Ecologically Successful River
Restoration

• Both pre- and post-assessment must be completed
  and data made publicly available.

22
Indicators

• Available documentation of preconditions and post
  assessment

23
Suggested Sixth Standard

• The guiding image be supplemented by some
  description or prediction of the ecological
  mechanisms by which the intended restoration
  strategy will achieve its goal

24
Comment on Resilience

• Perhaps the key issue for practitioners trying to
  satisfy this criterion is the ability to measure
  the improvement, and for this it is necessary to
  specify a time scale.

25
Comment on Resilience

• This specification of temporal scale would be
  part of our proposed sixth criterion because
  explanation of the mechanism invokes hypotheses
  that must identify spatial and temporal axes for
  a given process and/or target indicator, along
  with some indication of the size of biological
  effect.

26
Practioners Critique

• We suggest that by increasing factors of safety
  and incorporating large immobile structures, a
  project is driven away from ecological
  restoration towards the category of erosion
  control and containment

27
Practioners Critique

• Projects relying on fixed, in-place structures
  that resist or impede natural channel evolution
  contradict natural channel behavior, which is a
  component of ecological integrity.
• Restoration projects should utilize natural
  processes to create and maintain habitat, and
  should favor the use of native materials.

28
Practioners Critique

• The concept of launching a river restoration
  project by first establishing a guiding image
  with a dynamic ecological end state is the most
  critical aspect of a restoration project.
• In the real world of project development, guiding
  image development is far too often abbreviated,
  restricted by preconceived ideas and
  self-interest, hampered by lack of experience, or
  stripped of original intent by either
  bureaucratic process or sponsor/stakeholder
  reluctance to accept uncertainty and risk,
  leading to a number of poorly conceived projects.

29
Causes of Unforeseen Project Hardening

• A tendency to reduce project risk continually by
  increasing factors of safety during the design
  process.
• In a natural channel environment with
  unpredictable disturbance regimes, sponsors are
  commonly averse to adopting the level of risk
  necessary for true ecological restoration. A
  low level of risk tolerance, such as the commonly
  adopted 100-year flood, is such a high threshold
  that it almost always forces projects away from
  restoration techniques that anticipate channel
  changes of shape through time.
• Tight deadlines and/or budget constraints that
  preclude the development and adoption of natural
  process-driven alternatives.
• Bureaucratic requirements that, because of
  established and dogmatic patterns of practice,
  reduce opportunities for true restoration design,
  resulting in hard engineering solutions through
  precedent.
• Over-reaction to even moderate channel
  adjustments in a restored channel often leads to
  overly aggressive site repair. This hardening
  can be the result of the initial adoption of an
  unrealistic guiding image that anticipated full
  ecological benefits without acceptance of any
  risk of project distortion, adjustment or failure
  during a channel-changing flow event.

30
Causes of Unforeseen Project Hardening

• A tendency to reduce project risk continually by
  increasing factors of safety during the design
  process.

31
Causes of Unforeseen Project Hardening

• In a natural channel environment with
  unpredictable disturbance regimes, sponsors are
  commonly averse to adopting the level of risk
  necessary for true ecological restoration. A
  low level of risk tolerance, such as the commonly
  adopted 100-year flood, is such a high threshold
  that it almost always forces projects away from
  restoration techniques that anticipate channel
  changes of shape through time.

32
Causes of Unforeseen Project Hardening

• Tight deadlines and/or budget constraints that
  preclude the development and adoption of natural
  process-driven alternatives.
• Bureaucratic requirements that, because of
  established and dogmatic patterns of practice,
  reduce opportunities for true restoration design,
  resulting in hard engineering solutions through
  precedent.

33
Causes of Unforeseen Project Hardening

• Over-reaction to even moderate channel
  adjustments in a restored channel often leads to
  overly aggressive site repair. This hardening
  can be the result of the initial adoption of an
  unrealistic guiding image that anticipated full
  ecological benefits without acceptance of any
  risk of project distortion, adjustment or failure
  during a channel-changing flow event.

34
NOW
35
Gospel According to Stan

• Ecosystem restoration is based on restoring the
  ability of systems to maintain natural
  trajectories of physical and ecological
  functions.

36
Gospel According to Stan

• First, do no harm.

37
Gospel According to Stan

• If you have not restored process, structural
  changes are just short-term repair.

38
Gospel According to Stan

• If faced with a choice of a reversible action or
  an irreversible action and the outcomes and
  uncertainties are roughly equal, choose the
  reversible action.

39
Gospel According to Stan

• Practices that caused resource degradation must
  be changed to prevent continued loss of habitat,
  function, or species.

40
Gospel According to Stan

• Changes in resource management practices should
  precede restoration efforts to the degree
  possible.

41
Gospel According to Stan

• Restoration that uses natural materials and
  native organisms within their natural ranges of
  abundance and distribution is more likely to be
  effective over the long term.

42
Gospel According to Stan

• Ecosystems are dynamic and changing. Restoration
  simply to a previous condition often is
  impossible or ecologically undesirable.

43
Gospel According to Stan

• Evaluation of restoration efforts based on the
  simple criterion of persistence is just as static
  and ecologically inconsistent as the attempts to
  erect permanent structures or maintain fixed
  conditions.

44
Gospel According to Stan

• Evaluation of restoration efforts should be based
  on the ability of the system to attain the stated
  physical and ecological goals without continued
  human intervention.

45
Gospel According to Stan

• We all have a tendency to preach about
  restoration---either for or against.
• The practice of restoration will lead you neither
  to heaven nor to hell.