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always look beyond the boundaries of the ecosystem to protect its connections to
other systems in the landscape. The need for this approach to nature conservation
arises from the increasing degree of landscape fragmentation (e.g. Soons
et al
.
2005). Indeed, fragmentation into small patches has dramatic consequences for
biodiversity and for environmental quality in catchments that originally had a
high degree of landscape connectivity. A small patch size leads to high extinction
and the high degree of isolation to low colonization, resulting in a severe loss of
species richness of patches and of the landscape as a whole (Hanski 2005).
A second consequence of landscape fragmentation (e.g. from agricultural
intensification) is a drastic change in hydrology. Drainage of agricultural land has
resulted in lower groundwater tables, loss of groundwater discharge in (semi-)
natural landscape patches, straightening of low-order streams, dampening of
stream water level fluctuations, loss of floodplain habitat, loss of meandering as
a natural stream habitat process and a deterioration of stream water quality
(Brierley & Stankoviansky 2002). These changes have led to drastic changes in
diversity of habitats across the landscape, even in protected reserves with
appropriate internal management. It is evident that these landscape-scale
modifications have resulted in additional losses of biodiversity, which have
probably been just as severe as those caused by fragmentation
per se
.
Identification of OLUs, which are defined as 'combinations of landscape patches
with their biotic and hydrogeological connections', has recently been proposed as a
tool to facilitate wetland restoration in catchments with a high degree of
fragmentation and strongly altered hydrology (Verhoeven
et al
. 2008). The
combined consideration of biotic (i.e. dispersal, transports of organisms) and
hydrological (flooding events, groundwater flowpath connections across the
landscapes) factors is novel in this context. To synthesize the OLU for a specific
restoration project, the following three-step approach can be used. In the first step,
focus is on defining the restoration targets. Which plant or animal species or
community needs to be restored? Alternatively, which ecosystem function is to be
restored (e.g. water quality enhancement or floodwater detention)? What are the
reference conditions for the restoration that can be used to set the restoration
target? The second step identifies the features of hydrology and dispersal that are
crucial for the species, community or ecosystem to be restored. It may be that such
spatial mechanisms are not relevant for the species or system to be restored, in
which case conservation or restoration of individual patches is sufficient and the
OLU approach may not be appropriate. But in most cases, linkages play an important
role. The third step is to define the extent of the OLU by identifying the landscape
components which are necessary as building blocks for restoration of (i) hydrological
functioning and water regime and (ii) dispersal of plant and/or animal species.
The OLU approach will often involve the identification of 'source areas' (i.e.
intact, species-rich nature reserves which need to be conserved), as well as 'receptor
areas' which would be suitable for restoration and encompass the restoration target
area and connecting pathways such as streams or other hydrological flow paths. To
identify the receptor areas and connecting pathways, historical maps and other
records of present and past hydrological functioning are useful. A necessary
further step for the identification of the OLU is the creation of a map that
represents the combination of landscape elements that are required for regional
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