Linking Restoration and Ecological Succession (Springer ... - Inecol

176 Richard J. Hobbs et al.
“State”
Time
Figure 8.2 Classical restoration trajectory (solid line) and increasingly wider targets
(dashed and dotted lines) reflecting unpredictability or variability of endpoints and multiple
potential outcomes for restoration. Options can expand or contract through the
restoration process.
Precise restoration of original species assemblages and/or ecosystem functions
is almost always unrealistic because of the dynamic nature of disturbance
and changing reference systems. If we think in terms of restoration trajectories
(Fig. 8.2), the general aim in restoration is to move the system from its current
(degraded) state to a stable target state. Diagrams usually depict this with
a single arrow joining the current and target states. However, it has to be acknowledged
that there are numerous factors that affect the predicted direction
and cohesiveness of the trajectory. These include factors that are beyond the
control of project managers, such as prolonged drought, and practical issues
that are part and parcel of fieldwork, including delays in supply or poor quality
materials. Options may contract due to unexpected loss of species (e.g.,
from surrounding habitat destruction, species extinction) or due to an inability
of the soil and belowground biotic systems to respond (e.g., crossing thresholds
for recovery for soil structure). Options may also increase if new species
(e.g., weeds) colonize, land use changes, or societal views change to be more
accepting and even demanding of novel rather than original systems (Hobbs
et al. 2006). Restoration trajectories will also undoubtedly be impacted by climate
change but in an unknown way (Harris et al. 2006). Hence trajectories
are likely to be more dynamic than usually depicted, and options may expand
or contract along the way. Adaptive management strategies are the best way
to deal with divergence from anticipated end-points. Although in many cases
restoration trajectories are less predictable than we would like, we suggest that
knowledge from succession theory can reduce the unpredictability. Restoration
needs to move toward an evidence-based paradigm and as pointed out earlier,
evidence can come from many sources.
The final stage of a restoration that aims for complete species replacement
is rarely achieved (see Chapters 2, 5, and 6). First, broad scale disturbances