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

156 Richard J. Hobbs, Anke Jentsch, and Vicky M. Temperton
highly degraded systems, called in older parlance “dis-climax” systems, can
be restored or naturally regenerate back to a state similar to that prior to the
major disturbance. Restoration can learn from how succession proceeds on
highly degraded systems. Degraded, naturally retrogressive seres can keep going
downhill, as can a system subjected to an anthropogenic disturbance. So, is
restoration trying to stop, reverse, and/or completely restart the succession (see
Chapters 4 and 5)?
The key aspects which do not allow for simple acceleration of successional
processes in restoration are generally related to threshold phenomena which occur
when a system has been degraded beyond its resilience or inherent capacity
to recover (Whisenant 1999, Hobbs and Harris 2001, Harris and van Diggelen
2006). Such thresholds, often difficult to identify and quantify before they are
crossed, may be biotic in origin, relating to species loss, gain, or altered dispersal
potential, or abiotic, relating to changes in the physical or chemical characteristics
of the environment (for instance, altered soil structure or chemistry). The
presence of such thresholds militates against a simple successional process and
results instead in the possibility of alternative states with the system “stuck”
in a particular state (at least in the time frames within which humans operate)
with little or no potential for further development without active intervention
to overcome the threshold phenomenon in evidence.
Another complication of accelerated succession as a simple restoration goal
is ongoing, irreversible change in the environment, such as accumulating atmospheric
nitrogen deposition. Such change may create novel landscapes in
the sense of environmental determinants for species assembly and successional
interaction. Often, restoration goals cannot rely on historical reference seres;
rather, they have to account for novel environments.
7.5 Combining Succession and Assembly
The succession and community assembly approaches can be viewed as complementary
and inherently have a lot in common. Clearly, the more mechanistic
models of succession, such as those described by Connell and Slatyer (1977) and
Noble and Slatyer (1980), can be interpreted in a community assembly framework
with observed dynamics being the result of impacts of various events
on the response of individual species and interactions among species. The inhibition,
facilitation, and tolerance models of Connell and Slatyer (1977), for
example, have a lot in common with so-called “priority effects” in the field of
community assembly rules (Drake 1991, Belyea and Lancaster 1999) whereby
the identity of the established species within an ecosystem has an effect on
newcomers to the system. Priority effects in assembly can also be negative
(competitive exclusion), positive (nurse–plant effects), or neutral (both positive
and negative) depending on, for example, the phenological phase of plants interacting
under nurse–plant conditions (e.g., Flores-Martínez et al. 1994). Hence,
concepts such as priority effects could simply be viewed as the renaming of
older concepts from the succession literature.
Similarly, the ideas of community assembly can be interpreted in a successional
context, especially where community assembly is considered in a
temporal context and abiotic as well as biotic factors are considered. This is
increasingly the focus of attention in community assembly studies (see Weiher