Geoscience Reference
In-Depth Information
and general resilience.
54
I consider the meaning of these terms and the
respective roles of these types of resilience in maintaining ecosystem
functionality in the following paragraphs.
The term
'
speci
ed resilience
'
is used to describe the reaction of some
cthreat.
55
It is concerned with the key
slow variables that determine a system
speci
cpartofasystemtoaspeci
guration, and with consid-
ering how impacts on them may affect the ability of an ecosystem as a
whole to retain its structure and functions.
56
For example, Walker and
Salt
'
scon
ip into an
alternative algae-clogged state if a threshold of one key variable, phos-
phorus content in nutrients, is crossed.
57
The resilience of the lake
declines as levels of phosphorus increase, pushing sediments to the
point where it can no longer be absorbed. A speci
'
s example of a lake ecosystem examines its potential to
ed resilience response
to this situation could include efforts to reduce the content of phospho-
rus in agricultural run-off waters or the introduction of
ltering plants or
algae-consuming zooplankton to the system.
58
Knowledge of variables of ecosystems and of stressors that may drive
them towards thresholds if they are not controlled is valuable for efforts
to prevent or address known threats to ecosystem functionality.
59
However, there are three respects in which governing activities to main-
tain speci
cient for reducing risks that ecosystems
will shift into undesirable alternative states, and may even heighten
them. The
ed resilience is insuf
rstisthatitisextremelyhardinpracticetodetectwhenan
ecosystem is vulnerable to undergoing a regime change.
60
The existence
of key variables for ecosystem structure or of thresholds for them may
not be known.
61
Changes in state have often been unexpected with their
54
Walker and Salt,
'
Resilience Thinking
'
, pp. 120
-
2; Walker and Salt,
'
Resilience Practice
'
,
pp. 67
-
105;C.Folkeetal.,
'
Resilience Thinking: Integrating Resilience, Adaptability and
Transformability
'
(2010) 15(4):20 Ecology and Society; S. R. Carpenter et al.,
'
General
Resilience to Cope with Extreme Events
'
(2012) 4 Sustainability, 3250.
55
Walker and Salt,
'
Resilience Thinking
'
, pp. 120
-
1; Walker and Salt,
'
Resilience Practice
'
,
p. 68.
56
Walker and Salt,
'
Resilience Thinking
'
, pp. 120
-
1; Walker and Salt,
'
Resilience Practice
'
,
74.
57
Walker and Salt,
pp. 68
-
58
'
Resilience Thinking
'
,pp.55
-
8.
Ibid
., p. 59.
59
Ibid
., pp. 120
-
1; Walker and Salt,
'
Resilience Practice
'
,pp.18
-
20.
60
Scheffer et al.,
'
Catastrophic Shifts
'
, 591, 595
-
6; R. Biggs et al.,
'
Turning Back From the
(2009) 106 Proceedings
of the National Academy of Sciences of the United States of America, 826.
61
Walker and Salt,
Brink: Detecting an Impending Regime Shift in Time to Avert It
'
Resilience, Adaptability,
and Transformability in the Goulburn-Broken Catchment, Australia
'
Resilience Practice
'
,p.90;B.Walkeretal.,
'
'
(2009) 14(1):12
Ecology and Society.
