p.27 At a general level, systems can be viewed as consisting of mixtures of positive and negative
feedbacks, with positive feedbacks tending to alter the nature of the system, and negative feedbacks tending to minimize these
changes (Chapin et al. 1996). Changes that strengthen positive feedbacks... can lead to a change in conditions...
that may exceed the tolerance of other components of the system. This, in turn, leads to destabilization and threshold changes.
Threshold crossings occur when positive feedbacks amplify changes in system characteristics in ways that exceed the buffering
capacity of negative feedbacks that tend to maintain the system in its current state or the current limits of the control
variables. Viewed from an adaptive management perspective, threshold crossings occur when changes in the system exceed the
adaptive capacity of the system to adjust to change (Groffman et al. 2006). Because systems have adapted to the natural variability
experienced in the past, anything that disrupts that variability can make them vulnerable to further change and amplified
instability (Walker et al. 2006; Folke, 2006).
p.27 The following is a partial list of factors that are believed to come into play in determining a system's
resilience, and sensitivity to threshold behavior (see also May and Lean, 2007):
1. A higher diversity of very weakly connected and subsuitable components are thought to enhance resilience...
[JLJ - Capablanca writes in A Primer of Chess, p.42, that a Queen and Knight might be more powerful than a Queen
and Bishop, perhaps for this very reason] ...
7. Increasing time lags involved in population regulatory responses can destabilize systems (May 1977) [JLJ
- the lack of an immediate ability to constrain an enemy piece can cause a situation of possible instability]
p.29-30 To manage risk associated with ecological thresholds, it is essential to be able to forecast
such events and to plan for and study alternative management scenarios... Such changes in methods and outlook as
the following may be required: ... Use near-term forecasting tools, statistical and otherwise that are appropriate to this
class of system... Continue to identify the characteristics of systems that make them more or less vulnerable... Continue
to identify early warning signs of impending threshold changes (and to monitor for those signals)... Employ adaptive
management strategies, such as skillful short-term forecasting methods coupled with scenario exploration models that
are capable of dealing with successional scenarios and novel combinations of species [JLJ - or, interacting agents].
p.88 Under some conditions, thresholds may be recognized when changes in the rate of fine-scale processes
within a defined area propagate to produce broad-scale responses (Gunderson and Holling, 2002; Redman and Kinzig, 2003). In
these cases, fine-scale processes interact with processes at broader scales to determine system dynamics... Conceptual models
are particularly useful in linking hierarchical models across scales, because the existence of cross-scale interactions are
often clearly recognized and can be incorporated as rules, even if they cannot be precisely parameterized. Field experiments
that identify cause-and-effect relationships can then be implemented to test these cross-scale interactions.
p.89-90 Recent theories and ideas about system behavior have used hierarchy theory as a basis for describing
interactions among processes at different scales. Such theories include complex systems... self-organization... panarchy,
... and resilience... Cross-scale interactions... are an integral part of all if these ideas... These interactions generate
emergent behavior that cannot be predicted based on observations at single or multiple independent scales... the relative
importance of fine- or broad-scale pattern-and-process relationships can vary through time and compete as the dominant factors
controlling system dynamics... It is important to identify the key processes involved in these changing pattern-and-process
relationships so that thresholds can, at a minimum, be understood and predicted if not averted through proactive measures.
p.96 A key component of adaptive management strategies is the role of experimentation. A critical
component of designing appropriate experiments is to identify the conditions or systems that are susceptible to threshold
behavior and interactions across scales that include transport processes at intermediate scales. Observations and
experiments to evaluate the sensitivity of these processes and interconnections to anticipated perturbations provide insight
to management strategies to enhance resilience or to mitigate threshold changes.
p.98 The key to reducing stressors is to identify the factors that influence resilience.
In many cases, management practices that increase resilience can be designed from existing knowledge; in
other cases, however, it is not clear what management practices will enhance resilience
p.102 The gaps identified include the need to increase the resilience of ecosystems and reduce multiple
stressors to avoid threshold crossing. Both of these challenges are difficult to plan for but also are consistent with managing
ecosystems under conditions of uncertainty such as climate change. After a threshold crossing occurs, viable options are to
increase coping mechanisms, adaptive capacity...
