Geoscience Reference
In-Depth Information
bacterioplankton and invertebrates.
28
Studies of ecosystems where such
change has occurred reveal that it may not be possible to restore an
ecosystem to its former state simply by reducing the drivers of change to
below the level of the thresholds whose crossing triggered the shift.
29
Reduction to much lower levels than those that led to change may be
necessary in some cases whilst Walker and Salt fear that, in others, the
crossing of a threshold may represent
.
30
An additional
problem is that the complexity of ecosystems and the multiplicity of
sources of human and natural disturbances that affect them may make
it extremely dif
'
aone-waytrip
'
cult to develop plausible hypotheses for the causes of
change.
31
2.2.3
Interaction between ecosystems and the Earth System
It is not suf
cient, when assessing the ecological consequences of human
activities, to examine direct effects on ecosystems alone. We must also
consider the relationship between ecosystems and the Earth System.
Could the deterioration of ecosystem functionality affect Earth System
processes? If so, what feedback effects could change at the global scale
have on the functioning of ecosystems?
Steffen and his colleagues de
the suite of
interacting physical, chemical and biological global-scale cycles
ne the Earth System as
'
...
and
energy
uxes which provide the conditions necessary for life on the
.
32
Earth System processes include the climatic system, the hydro-
logic cycle and the biogeochemical cycling of gaseous elements that
regulates atmospheric composition.
33
Their in
planet
'
uence on the functioning
of ecosystems has long been recognised.
34
The cycling of elements and
water impacts signi
cantly on how ecosystem structures, functions and
properties evolve. In contrast, recognition of the in
uence of ecological
processes at the planetary scale is relatively recent although it is now
widely thought that these play a signi
cant role in shaping elements
28
E. A. Norse,
in E. A. Norse
and L. B. Crowder (eds) Marine Conservation Biology: The Science of Maintaining the
Sea
'
Ending the Range Wars on the Last Frontier: Zoning the Sea
'
sBiodiversity(Washington, DC: Island Press, 2005), p. 423.
29
Walker and Salt,
'
'
Resilience Practice
'
,pp.6
-
9; C. R. Allen et al.,
'
Commentary on Part
One Articles
in L. H. Gunderson, C. R. Allen and C. S. Holling (eds) Foundations of
Ecological Resilience (Washington, DC: Island Press, 2010), pp. 7, 10
'
-
11.
30
Walker and Salt,
'
Resilience Practice
'
,p.9.
31
S. R. Carpenter,
'
Ecological Futures: Building an Ecology of the Long Now
'
(2002) 83
Ecology, 2074.
32
33
34
Steffen et al.,
'
Global Change
'
,p.7.
Ibid
.
Ibid
., p. 24.
