Environmental Engineering Reference
In-Depth Information
Target plant species such as
A. montana
do not
spread or re-establish after sod cutting in overgrown
heathland. Immediately after sod cutting, the level of
ammonia increases sharply (Dorland
et al
. 2003). This
turns out to be harmful for
Arnica
seedlings (De
Graaf
et al
. 1998a). The addition of chalk, to increase
the buffering capacity of the soil, may compensate for
this negative effect (van den Berg
et al
. 2003).
8.4 Restoration of degraded ecosystems
Dry grasslands and heathlands with most or at least
part of the characteristic species still present can
be managed by the continuation or re-instalment of
practices inherent to the former low-intensity farming
systems, such as mowing, cutting sods, grazing and
burning. In Europe, this implies continuation of the
still-existing low-intensity farming system in countries
such as Greece, Spain, parts of France and the UK
(Bignal & McCracken 1996). In other countries existing
dry grasslands and heathlands are often nature reserves.
Here the management in charge of nature conserva-
tion has more or less taken over the former farming
practices. However, this is not always successful.
8.4.3 Grazing
The success of grazing in heathlands overgrown by
grasses depends on the species of herbivore introduced.
Sheep grazing is less successful than cattle grazing.
The introduction of sheep seems appropriate, as sheep
grazing and heathland exploitation are strongly
related. However, it has become clear that sheep were
only used during the past two centuries. Before 1800,
cattle grazing was practised more in heathlands in
the Netherlands. Cattle grazing was successful in
reducing the grass
Deschampsia flexuosa
(Bokdam &
Gleichman 2000), and a cyclic successional pattern has
been suggested (Bokdam 2003).
The introduction of livestock grazing in prairie
management is heavily debated in North America.
This has partly to do with the wilderness concept of
nature conservation, which ignores the concept of semi-
natural landscapes. Wedin (1992) has compared the
approaches of management of tallgrass prairie in the
USA and of the semi-natural landscapes in Europe,
and he advocates introducing the European practices
to North America. Grazing by large herbivores in tall-
grass prairie generally increases plant species richness
as a result of the creation of a mosaic of patches
(Collins
et al
. 1998, Knapp
et al
. 1999). Gazing by bison
resulted in high light levels at the soil surface and
heterogeneity of the high light levels in the vegeta-
tion. Moreover, with bison grazing a positive correla-
tion was found between species turnover (extinction
and colonization) and species richness (C. Bakker
et al
.
2003).
8.4.1 Mowing
Mowing regimes should be applied in a proper way
as can be deduced from the following example.
Calcareous grasslands in Dutch nature reserves were
cut in late autumn to stimulate seed rain of the
target species present. However, the grass
B. pinna-
tum
became dominant, and this resulted in a decline
of characteristic species, mainly forbs. Experiments
revealed that early cutting (July) prevented the
reallocation of nutrients to below-ground storage
organs of the grass. The early cutting regime showed
a decrease of
B. pinnatum
and an increase in species
richness (Bobbink & Willems 1991).
8.4.2 Sod cutting
Sod cutting in heathlands overgrown by grasses is suc-
cessful for matrix plant species such as
C. vulgaris
and
Erica tetralix
. Initially, cutting was carried out by hand,
but later machinery became involved. The latter was
also thought to be economically feasible. The sods were
stored and after a freezing period sold for horti-
cultural purposes. This type of industrial sod cutting
on a large scale has the positive benefit of removing
nutrients. However, it is detrimental for animals
such as amphibians and invertebrates. These animals
favour a mosaic of different structures of the veg-
etation in their habitat. Therefore, mechanical sod
cutting should be a small-scale practice.
8.4.4 Burning
Burning of heathland overgrown by grasses was
practised in the Netherlands until 20 years ago. As the
