Principles of terrestrial ecosystem ecology.pdf

364 16. Managing and Sustaining Ecosystems
recognition of the dynamic character of ecosystems;
(6) attention to scale and context; (7)
inclusion of humans as a component of
ecosystems; and (8) incorporation of adaptive
approaches (Christensen et al. 1996). Most
integrated ecosystem management programs
explicitly facilitate public participation and
collaborative decision making.
Long-term sustainability is the fundamental
objective of ecosystem management. It is
achievable in part via the inclusion of sound
ecological models and understanding that
incorporate the complex and dynamic character
of ecosystems and acknowledge humans as
inherent components of ecosystems. Change
and uncertainty are intrinsic characteristics of
most ecosystems, and ecosystem management
is an approach that acknowledges the occurrence
of stochastic events as well as predictable
variability (Holling 1993). Ecosystem management
must therefore be flexible enough to learn
from scientific analysis and advances and
to adapt to institutional and environmental
change.
An ecosystem management approach is
especially critical for the management of
complex systems such as watersheds and
marine fisheries, where management must consider
multiple changes and the linkage among
ecosystems through the movement of water, air,
animals, and plants. The ocean ecosystem that
is relevant to salmon fisheries combines freshwater
rivers and streams, coastal ecosystems,
intermediate continental shelf waters, and the
deep ocean, all of which are characterized by
complex dynamics that vary in space and time
in ways that are poorly understood. The complexity
and scales of change in marine ecosystems
are only partially understood, including
seasonal variations in productivity, regionalscale
El Niño climatic events, and long-term
changes in salinity and ocean temperature.
Large natural fluctuations in the abundances of
marine fish are the rule more than the exception.
Our limited powers of direct observation
also result in a fragmented knowledge of the
diversity, abundance, and interactions of marine
organisms. One challenge of ecosystem management
is to reconcile the disparity between
the spatial and temporal scales at which
humans make resource management decisions
and those at which ecosystem properties
operate (Christensen et al. 1996).
Ecosystem management goes beyond a
single focus on commodity resources and harvesting
limits. Instead, it embraces sustainability
as the criterion for commodity provision
and/or other uses. Ecosystem management is
therefore concerned with multiple functions,
thresholds in processes, and trade-offs among
different management consequences. It frequently
considers, for example, both productivity
and biodiversity (Johnson et al. 1996). All
ecosystem management projects strive for an
integrated understanding and management of
the ecological, social, economic, and political
aspects of resource use to maximize long-term
sustainability (Box 16.2).
Adaptive management, involving experimentation
in the design and implementation of
policies, is central to effective management of
ecosystems. An adaptive policy is one that is
designed from the outset to test hypotheses
about the ways in which ecosystem processes
respond to human actions. In this way, if the
policy fails, learning occurs, so better policies
can be applied in the future. Perhaps as a result
of frequent management failures and gaps in
scientific knowledge, the concept of adaptive
management has become central to the implementation
of ecosystem management. One
advantage of adaptive management stems from
the high degree of uncertainty in real-life
complex systems. Instead of delaying timely
action due to the lack of certainty, adaptive
management promotes the opportunity to learn
from management experience. The lack of
action in the face of uncertainty can have
ecosystem and societal consequences that are
at least as great as actions based on reasonable
hypotheses about how the ecosystem functions.
Hypotheses that underlie adaptive management
may consider the probabilities of both
desired outcomes and ecological disasters
(Starfield et al. 1995). The optimal policy,
for example, may be one that has a moderate
probability of desirable outcomes and a low
probability of causing an ecological disaster.
While hundreds of projects have embraced
an ecosystem management perspective, most