Environmental Engineering Reference
In-Depth Information
14.1 INTRODUCTION:
CHARACTERISTICS OF DRY
GRASSLANDS AND HEATHLANDS
Both result in the disappearance of the characteristic
species of open, oligotrophic ecosystems. The main
task of restoration under these conditions is to achieve
the right nutritional soil conditions in order to enable
and facilitate the persistence and/or re-establishment
of target species and communities. Primary constraints
for restoration of these ecosystems are (1) the high
nutrient status of the soil and (2) limited seed longevity
and seed dispersal abilities of species targeted for
reintroduction.
Dry grasslands, and heathlands, as well as dry
coastal dune grasslands, can be characterized from a
hydrological point of view as infi ltration areas, fed by
rainwater. Here, restorationists do not have to deal
with complicated groundwater management issues as
is the case for mires (see Chapter 16). The traditional
view is that after the last glacial period, natural com-
munities of dry grasslands and heathlands occurred
on rocky inland outcrops, for example as chalk grass-
lands, along coasts (heathlands on rocks and dune
grasslands on mobile sands), in river fl oodplains and at
the edge of bogs. Their area was restricted to marginal
habitats with extreme abiotic conditions such as
shallow soil with subsequent low nutrient availability.
In Europe, an agricultural farming system was intro-
duced from the Middle East after about 7000
BP
and
spread quickly. In north-western Europe, agriculture
started at about 5000
BP
in the northern part of the
Netherlands (Spek 2004) and Germany (Behre 2008).
Apart from arable fi elds, common grazing lands were
exploited and resulted in the extension of grasslands
and heathlands in the Atlantic part of Europe (i.e. from
southern Norway to northern Portugal, and up to
about 200 km inland). Domestic livestock has most
likely dispersed many plant species from the Middle
East into Europe (Bonn & Poschlod 1998).
Trans-
humance
, the seasonal movement of livestock to
another region, must have played an important role in
the long-distance dispersal of diaspores (Poschlod &
Bonn 1998 ; Ozinga
et al
. 2009 ).
Dry grasslands and heathlands developed under a
grazing system with common grazing rights, based
mainly on cattle and sheep. The practice of hay cutting
developed only during the last 2000 years, to provide
winter forage for animals such as oxen and horses used
for traction in pulling farm instruments such as
ploughs. The removal of biomass from the fi elds resulted
in a reduction in soil fertility, which is a characteristic
phenomenon of low - intensity farming systems.
Although good examples of low-intensity grassland
Inland and coastal dry grasslands and dry heathlands
harbour characteristic plant and animal communities
on mesotrophic or oligotrophic soils. We focus on these
communities in Europe, with its industrialized and
densely populated countries. As similar problems exist
to a certain extent elsewhere, we will also pay attention
to grasslands in North America. For Europe, we follow
the European Nature Information System (EUNIS
2006). This is a supranational instrument providing
for a common framework for the conservation of plant
and animal species and their natural habitats within
the 27 member states of the European Union. This
classifi cation is the basis for the creation of a European
network of Special Areas of Conservation, a major
constituent of Natura 2000. We will be concerned
with EUNIS habitat types E1 Dry grasslands, F4 Tem-
perate shrub heathland and B1 Coastal dunes and
sandy shores. Note that we consider the EUNIS catego-
ries as
reference
communities for purposes of con-
servation, and their defi ned species assemblages as
appropriate targets for restoration programmes in
grasslands
and
heathlands
anywhere.
These EUNIS reference communities are of course
heavily infl uenced by human activities, as it is assumed
that human impact was a major factor increasing
the area of dry grasslands, dune grasslands and
heathlands, primarily as a result of agricultural exploi-
tation during the past millenia, in what is nowadays
referred to as low-intensity farming systems (Bignal &
McCracken 1996). This is particularly the case in
Europe where almost all dry grasslands, dune grass-
lands, and heathlands are
seminatural landscapes
(Thompson
et al
. 1995). Such systems can only be
maintained by low-intensity farming or proxy land
management techniques, as either intensifi cation or
extensifi cation (i.e. the abandonment of any kind of
management) will change the communities. One key
question for restorationists to explore is whether such
changes are reversible or not.
Sites where low-intensity agriculture is no longer
economically feasible are at risk, from both intensi-
fi cation, in some areas, and abandonment, in others.
Intensifi cation often leads to eutrophication of the soil.
In contrast, agricultural abandonment triggers sec-
ondary succession from open grasslands or heathlands
to shrublands and, eventually, woodlands or forests.
