Geoscience Reference
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probability of disturbance. Consequently, steady-state equilibrium may only be
observable or predictable at medium scales, and even at these scales non-linear
responses or threshold effects may occur to create different states (fi gure 25.6).
An example of this can be seen in aquatic and riparian habitat turnover along
an island-braided reach of the natural and dynamic River Tagliamento in Italy. Van
der Nat et al. (2003) demonstrate that 75 percent of aquatic and 29 percent of
vegetated island habitat was restructured over a 2.5-year period due to frequent
channel movements, while Zanoni et al. (in press) examine habitat restructuring in
the same reach, and conclude that although habitat rearrangement occurs fre-
quently, over medium timescales (decades) the cover of different habitat types
remains relatively constant. Over longer timescales (centuries), morphological
changes along the river, along with variation in sedimentary processes and wood
delivery, may result in these habitats changing notably or disappearing from a given
reach completely (Spaliviero, 2003). Consequently, the degree of equilibrium appar-
ent in a system depends on the spatial and temporal scale under consideration.
Unfortunately, much land and resource management is conducted with the
concept of steady-state equilibrium in mind. Whereas such steady state equilibrium
can only be said to exist at 'medium' scales (fi gure 25.6), management is typically
conducted at relatively fi ne spatial and temporal scales (years to decades at best),
where greater dynamism and variability are more typical. This mismatch creates
problems for land management and prediction and can lead to unsustainable land-
use practices. In effect, the concept of equilibrium states is subjective, diffi cult to
quantify and may be misleading or inappropriate in a management context.
Measuring Variability in Ecosystems and
Ecosystem Components
Measurement of variability in ecosystem pattern and process to inform decision
making is an applied problem for ecologists, environmental geographers, and land
managers. Comprehensive ecosystem measurement would require investigations of
a multitude of processes by a large range of specialists in varying disciplines. Con-
sequently, investigations into the variability of ecosystem patterns and processes are
focused on a limited subset, and are necessarily limited in size and scope. Due both
to the increasing acknowledgement that ecosystems are interconnected, open systems
and to the consequent increase of management at the landscape or catchment level,
there is now a move towards measuring variability at the landscape scale by geo-
graphers and landscape ecologsts using remote sensing techniques and landscape
metrics analysis (e.g., Batchelor et al., 2002; Caseldine and Fyfe, 2006).
Measurements are usually conducted over a range of temporal scales using dif-
ferent techniques. Longer-term analysis of ecosystem variability is performed using
landscape interpretation and reconstruction (e.g., Delcourt and Delcourt, 2005;
Caseldine and Fyfe, 2006). Short-term measurements are more common for manage-
ment and involve looking at spatio-temporal variability in ecosystem components,
for example population and community dynamics, habitat turnover and heterogene-
ity, fl uxes of carbon and water, and so on. Even within relatively simple ecosystems,
such as agricultural systems, intensively managed for the production of a single
resource over short temporal scales, a wide range of measurements need to be taken
to quantify variability and allow even coarse predictions (table 25.2). The develop-
ment and application of new geographical technologies are central to measurement
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