Restoration of Dry Grasslands and Heathlands - Restoration Ecology: The New Frontier - page 186

of seeds in the soil, and the poor dispersal capacity of
many organisms, is needed in order to set realistic
targets in restoration of dry grasslands, dune grass-
lands and heathlands. Otherwise, the need for deliber-
ate reintroduction of species should be taken into
account while recalling that spontaneous establish-
ment of certain plant species may pose problems by
outcompeting species targeted for reintroduction.

to allow dispersal. Unfortunately, herbivores may
enrich the sites by depositing their dung, while the
seeds they introduce in this way seem to originate
mainly from species in the sites with the highest nutri-
ent levels, which harbour better forage quality for the
herbivores (Mouissie et al . 2005a ). Indeed, dispersal
occurs, but in the wrong direction.
Even when nutrient-poor abiotic conditions are
achieved, the restoration of dry grassland, dune grass-
land and heathland communities is limited by dispersal
of target species (Bakker & Berendse 1999) and subse-
quent germination and establishment (Baeten et al .
2009). The importance of the 'moving ecological infra-
structure' such as free-ranging animals (Ozinga et al .
2009) and humans (Strykstra et al . 1996 ) is underes-
timated. Experiments with the introduction of seeds or
hay show that poor dispersal can be overcome. A solu-
tion could be the introduction of hay from nearby refer-
ence communities (see Chapter 8), which enhances the
chance that seeds with similar genetic backgrounds are
introduced from the local species pool.
When spontaneous re - establishment of species does
not occur, deliberate reintroduction can be consid-
ered. Many authors advocate the advantages of spon-
taneous re-establishment as a strategy instead of
actively introducing species (e.g. Prach et al . 2001 ) but
there are also large seed production programmes rou-
tineously used in grassland restoration programmes
(Jongepierova 2008; see also Chapter 15). Notwith-
standing differences in opinion, all experts agree that
there are certainly dangers involved in a widespread
application of deliberate reseeding. Not only may prop-
agule addition determine future developments and
block alternative developments but it may also enhance
the dispersal of nonlocal genotypes (see also Chapter
7). It depends on the breeding type of individual species
whether this is a problem. Plants establishing from
propagules of local or regional populations often show
better performance than genotypes from elsewhere
(Vander Mijnsbrugge et al . 2010) and using the latter
may result in decreased restoration results. Because of
these potential dangers, conservation agencies in some
countries, such as the Netherlands and Switzerland,
have formulated rather strict guidelines concerning
the conditions under which species introduction is
allowed (Rometsch 2009). In the Netherlands, nature
conservation agencies deal with the following consid-
erations for plants that have disappeared from the
established vegetation. It should be clear from historic
records that the species previously occurred in the

14.5.1 Nutrient reduction

As mentioned at the outset of this chapter, one of the
main constraints for restoration of grassland and
heathland ecosystems derive mainly from the exces-
sively high nutrient status of the soil of abandoned
agricultural fi elds and pastures. Modelling the effects
of management and atmospheric deposition on Calluna
vulgaris on lowland heaths in the United Kingdom
revealed important interactions. More frequent cut-
tings of this emplematic species were required with
high rainfall when atmospheric deposition was also
high. These regional variations must be taken into
account when defi ning critical loads of nitrogen in
atmospheric depositition or designing management
prescriptions (Britton et al . 2001 ). Long - term haymak-
ing can remove nutrients up to the level of mesotrophic
communities. Further oligotrophication is only likely to
be achieved using sod cutting or topsoil removal. It
certainly enhances the transformation of plant com-
munities towards the targets in habitats when the
requirements for other abiotic conditions are met.
Grazing can only be successful to reach oligotrophic
conditions when the herbivores are introduced after
several years of frequent haymaking or after sod
cutting or topsoil removal.

14.5.2 Dispersal and re-establishment
of species

The other major constraint we have considered is
related to limited seed longevity and seed dispersal
abilities of target species. Solutions must therefore be
sought. As mentioned above (Figure 14.2), grazers can
disperse seeds through their dung (Mouissie et al .
2005a) or in their fur (Mouissie et al . 2005b ). Grazed
sites often include a mosaic of eutrophic and meso-
trophic sites to be restored and still-existing dry grass-
land and heathland communities on oligotrophic soils