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

124 Karel Prach et al.
affecting successional pattern in a comparative study of 15 unassisted successions
in various human-made habitats in central Europe (Prach et al. unpubl.).
These studies suggest that manipulation of soil pH might be a useful tool for
accelerating and directing succession toward specific targets.
In many systems, low nutrient availability assists restoration because it restricts
the growth of competitive, nontarget species. This generalization appears
valid for nutrient-rich landscapes such as in temperate Europe, but not in extreme,
marginal areas (Whisenant 1999). Low-fertility substrates often provide
good establishment opportunities for those species that are weak competitors on
fertile sites. Thus, these infertile sites can serve as refugia for rare and endangered
species retreating from nutrient-enriched landscapes (Benkewitz et al.
2002, Pywell et al. 2003). Nutrient levels can be easily increased, but not so
easily reduced by manipulation (Perrow and Davy 2002).
6.3 Methodological Approaches
6.3.1 Moving Succession Toward a Target
Three different strategies can be envisaged for creating new ecosystems during
ecological restoration, representing a gradient of management and intervention
intensity to manipulate succession:
(i) The simplest approach is to leave the site without intervention (unassisted
succession; Parker 1997, Prach et al. 2001, Walker and del Moral 2003);
successional development then proceeds at its own pace, but will be substantially
affected by the local species pool. This strategy is sometimes
slow, taking decades or even centuries, and it is often difficult to ensure
that the final target ecosystem is met. However, costs to implement this
strategy are low as long as no goods or services are affected.
(ii) At the other end of the spectrum is a technical solution to reach a target.
Here, many abiotic variables can be altered, and biota and biotic processes
can be more or less controlled by introducing desirable species. While
there is still a role for colonizing biota, it is likely that locally derived
biota will have a reduced importance as establishment into developed or
developing vegetation may be more difficult due to additional competition
from sown or planted species.
(iii) Between these extremes there is an approach where spontaneous succession
is assisted by limited physical or biotic manipulations. Physical manipulation
of succession may rely on improving the site and then allowing
spontaneous succession, i.e., relying on colonization processes to create
the community species pool. With biotic manipulation, adding some biota
artificially or controlling established, nontarget species enhance colonization.
The increase in management inputs moving from unassisted succession to a
technical solution can be viewed as a sequential removal of barriers (filters) to
species colonization and persistence (Temperton 2004; see Chapters 2 and 7).
In the early stages of spontaneous succession there are a number of physical,
chemical, and dispersal barriers to species establishment. As succession proceeds,
these barriers are likely to decrease in importance and be replaced by