Environmental Engineering Reference
In-Depth Information
• The use of limited resources by the invaders (such as
water in arid areas) is another important criterion for
immediate action.
• In some cases, invasive alien species might have an
economic value (e.g. providing fi re wood for local com-
munities) or might have become integrated into native
ecosystem networks (e.g. pollination networks). In
such cases, adverse effects of harmful alien species and
the positive impacts have to be balanced, and the main
goal could be to prevent further spread of the alien.
to be quantifi ed and paves the way for an objective
consideration of potential trajectories under a range of
management interventions. Referring to two promi-
nent groups of invasive plants in South African fynbos
ecosystems, we have described a protocol for improving
decision making through explicitly addressing issues
relating to resilience. Further work is needed to bridge
the gap between understanding the full array of
impacts resulting from invasions and knowing how
this understanding can be used to formulate plans for
restoration. The key lies in further elucidation of
factors affecting ecosystem resilience. Implementation
of our threshold model in a wide range of ecosystems
is dependent upon answering key questions, such as:
'Which ecosystem properties and/or ecosystem func-
tions will give best indication of the target system's
resilience?', 'What are the links between resilience and
diversity (or species richness) of an ecosystem?', and
'How do we determine whether an ecosystem has
reached a threshold and changed to an alternative
stable state? '
20.6
PERSPECTIVES
Further large-scale degradation of ecosystems over
large areas of the globe seems inevitable in the coming
decades. Ecosystems in ' pristine ' or ' historical ' condi-
tion will become increasingly rare (see also Chapters 2
and 3). Even if we are able to restore highly degraded
ecosystems, outcomes might well be unexpected, and
the resulting
emerging ecosystems
, although closer
to a 'natural' state in terms of some criteria, are likely
to differ substantially from any historical condition
(Norton 2009). Under such conditions, any and all
management activities, including restoration actions,
are experiments (e.g. Roura-Pascual
et al
. 2010 ). Much
closer collaborations between managers and scientists
are crucial to achieve management goals (including
those relating to restoration) for these degraded
systems (Seastedt
et al
. 2008 ). Setting appropriate
goals for restoration is thus a task that demands sophis-
ticated planning. Explicit attention needs to be given to
the determinants of resilience and the identifi cation of
key thresholds. This allows for the level of degradation
ACKNOWLEDGEMENTS
MG and DMR acknowledge support from the DST-NRF
Centre of Excellence for Invasion Biology and the
Working for Water programme through their collabo-
rative research project, Research for Integrated Man-
agement of Invasive Alien Species. We thank Tony
Rebelo for very helpful discussions concerning the con-
ceptual framework and Sue Galatowitsch, Judy Fisher
and Olivier Filippi for their useful comments.
