Restoration of dry grasslands and heathlands - Restoration Ecology - page 109

showed that N mineralization rates in humus-
rich woodland soils were better correlated with the P
content of fallen leaves than with the amount of N.
This suggests that raised P levels will also result in
increased N availability. Moreover, when two or more
nutrients are limiting productivity, the system is less
sensitive to temporary rises in the availability of a
single nutrient. Sod cutting and topsoil removal,
however, are mainly effective for the removal of
nitrogen but much less for phosphorus (e.g. Verhagen
et al . 2004). Consequently, the productivity is only
limited by nitrogen availability and these systems are
more susceptible to small fluctuations in N input. This
is especially true in the framework of atmospheric depo-
sition that amounts up to 30-40 kg of N ha −1 yr −1 in
the Netherlands. Critical loads for the target commun-
ities are less than 20 kg of N ha −1 yr −1 (Bobbink et al .
1998). Modelling the effects of management and
atmospheric deposition on C. vulgaris revealed an inter-
action between the two. More-frequent cutting was
required with high rainfall when atmospheric deposi-
tion is high. This variation should be taken into
account when defining critical loads or designing
management prescriptions (Britton et al . 2001). Long-
term haymaking can remove nutrients up to the level
of mesotrophic communities. Further oligotrophication
is only likely to be achieved after sod cutting or top-
soil removal. It certainly enhances the transformation
of plant communities towards the targets in habitats
that sufficiently meet the other abiotic conditions.
Grazing can only be successful when the herbivores
are introduced after several years of frequent hay-
making or after sod cutting or topsoil removal.
Fencing of sites is only feasible when dispersal of nutri-
ents and non-target species into the oligotrophic
target sites can be prevented.

tion could be the introduction of hay from nearby
reference communities (see Chapter 7), which en-
hances the chance that seeds with similar genetic back-
grounds are introduced from the local species pool.
Another advantage is that managers in charge of con-
servation do not have to get rid of poor-quality hay
from reference sites.
Introduction experiments suggest that especially
rare plant species do not establish, even after the intro-
duction of seeds. Maybe they depend on special soil
organisms. These can be symbiotic mycorrhizal fungi,
or nematodes grazing on roots of competing species.
These soil organisms are supposed to disperse much
more slowly than the seeds of plants. Hence, the
limiting factor for establishment could be the absence
of these soil organisms. Experiments are advocated to
introduce soil from reference sites together with seeds
of target species.

8.7.3 Conflicting targets

Sites under restoration management should be
monitored for the establishment of target species of
plants, invertebrates - such as butterflies, grasshop-
pers and carabid beetles - and vertebrates, including
their presence in adjacent grid cells (1 km 2 ). This
will reveal data on the rates of dispersal and re-
establishment of different groups of organisms. Many
invertebrates and species of birds, mammals and
reptiles strongly depend on the structure of the vegeta-
tion, especially the spatial arrangement of bare soil,
short turf, tall forbs, scrub and forest (van Wieren
1998). This means that conflicts between different
nature-conservation interests can arise. Large-scale
industrial sod cutting and haymaking are positive for
a number of plants - although not all - in view of the
removal of nutrients, but negative for many animal
species. The latter need tall stands or litter accumu-
lated for shelter, oviposition and the development of
young animals. Restoration efforts should aim at the
development of complete communities and not just
plant communities of dry grassland and heathland
(Mortimer et al . 1998). A design of mosaics includ-
ing different successional stages and different scales
should be part of restoration management.
Setting ecological targets is necessary to prevent
conflicts. It should also be clear what the targets are

8.7.2 Dispersal and establishment of species

Even when the right abiotic conditions are achieved,
the transformation into dry grassland and heathland
communities is limited by dispersal of target species
(Bakker & Berendse 1999). The importance of the
'moving ecological infrastructure' such as animals and
humans is underestimated (Strykstra et al . 1996b).
Experiments with the introduction of seeds or hay
showed that poor dispersal can be overcome. A solu-