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

122 Karel Prach et al.
succession? Alternatively, when is manipulation of spontaneous succession or
technical reclamation needed to reach the targets?
6.2 Manipulation of Succession: A Framework
6.2.1 Spatial Scales
Two types of information can be obtained from restoration schemes where succession
has been manipulated: The first is from controlled experiments that
are typically small-scale (10−1 –102 m2 ) and last only a few years. Resulting
data can be tested rigorously, and have a potential to contribute to ecological
theory. However, their extrapolation to the scales at which most practical
restoration projects are implemented (103 –105 m2 ) is limited, and must be made
with caution (see Chapter 1). Second, there are general observations that are
obtained from practical restoration work. Such information is typically available
at larger scales but must also be used with caution because it cannot be
tested rigorously. Nevertheless, this observational information can be used to
generate hypotheses for subsequent testing and verification as well as in the
interpretation of the experimental data. Each restoration project ought to use
both types of knowledge.
Inevitably a great influence on any restoration scheme is the landscape context,
and how the treated area relates to its surroundings. An important constraint
on succession is the available species pool, which is determined by a combination
of factors, such as macro- and microclimate, areas of intact vegetation, landuse
history (Zobel et al. 1998), and by their spatial patterns. Propagule sources
in the close vicinity are important for the establishment of late-successional
species that usually have poor dispersal abilities (Poulin et al. 1999, Novák and
Prach 2003; see Chapter 2). Generalists, often present among early-successional
species, disperse more readily, and can colonize from a distance (Grime 1979).
Their participation in succession is often determined by their abundance in the
surrounding landscape and a mass effect is important (Settele et al. 1996). On
the other hand, seral stages on restored sites may serve as propagule sources
of generalists, including invasive aliens and weeds, for the surrounding landscape
(Rejmánek 1989). Various human activities in the surrounding landscape
influence the regional species pool and thus influence vegetation succession
in a restored site. Any intentional manipulation of propagule sources in the
wider landscape is, however, difficult. This is particularly true for generalists,
including aliens, with widely dispersed propagules (see Chapter 5).
6.2.2 Temporal Scales
6.2.2.1 Rate of Succession
In human-altered landscapes, recovery to late-successional communities with
a slow species turnover can take many decades, yet these communities are
often used as targets in restoration programs and succession is manipulated
to accelerate succession toward them. Under extreme site conditions, such as
china clay wastes in south-west England, unassisted succession can take a very
long time (>100 years) and patches devoid of vegetation can persist (Marrs and
Bradshaw 1993). At this site, technical manipulations can reduce the process
of succession to a sustainable ecosystem in as less as 7 years. However, in